| Message ID | 1388978467-2075-1-git-send-email-jasowang@redhat.com |
|---|---|
| State | Superseded, archived |
| Delegated to: | David Miller |
| Headers | show |
On 01/05/2014 07:21 PM, Jason Wang wrote: > L2 fowarding offload will bypass the rx handler of real device. This will make > the packet could not be forwarded to macvtap device. Another problem is the > dev_hard_start_xmit() called for macvtap does not have any synchronization. > > Fix this by forbidding L2 forwarding for macvtap. > > Cc: John Fastabend <john.r.fastabend@intel.com> > Cc: Neil Horman <nhorman@tuxdriver.com> > Signed-off-by: Jason Wang <jasowang@redhat.com> > --- > drivers/net/macvlan.c | 5 ++++- > 1 files changed, 4 insertions(+), 1 deletions(-) > I must be missing something. The lower layer device should set skb->dev to the correct macvtap device on receive so that in netif_receive_skb_core() the macvtap handler is hit. Skipping the macvlan receive handler should be OK because the switching was done by the hardware. If I read macvtap.c correctly macvlan_common_newlink() is called with 'dev' where 'dev' is the macvtap device. Any idea what I'm missing? I guess I'll need to setup a macvtap test case. And what synchronization are you worried about on dev_hard_start_xmit()? In the L2 forwarding offload case macvlan_open() clears the NETIF_F_LLTX flag so HARD_TX_LOCK protects the driver txq. We might hit this warning in dev_queue_xmit() though, net_crit_ratelimited("Virtual device %s asks to queue packet!\n", Perhaps we can remove it. > diff --git a/drivers/net/macvlan.c b/drivers/net/macvlan.c > index 60406b0..5360f73 100644 > --- a/drivers/net/macvlan.c > +++ b/drivers/net/macvlan.c > @@ -338,6 +338,8 @@ static const struct header_ops macvlan_hard_header_ops = { > .cache_update = eth_header_cache_update, > }; > > +static struct rtnl_link_ops macvlan_link_ops; > + > static int macvlan_open(struct net_device *dev) > { > struct macvlan_dev *vlan = netdev_priv(dev); > @@ -353,7 +355,8 @@ static int macvlan_open(struct net_device *dev) > goto hash_add; > } > > - if (lowerdev->features & NETIF_F_HW_L2FW_DOFFLOAD) { > + if (lowerdev->features & NETIF_F_HW_L2FW_DOFFLOAD && > + dev->rtnl_link_ops == &macvlan_link_ops) { > vlan->fwd_priv = > lowerdev->netdev_ops->ndo_dfwd_add_station(lowerdev, dev); > >
On 01/06/2014 03:35 PM, John Fastabend wrote: > On 01/05/2014 07:21 PM, Jason Wang wrote: >> L2 fowarding offload will bypass the rx handler of real device. This >> will make >> the packet could not be forwarded to macvtap device. Another problem >> is the >> dev_hard_start_xmit() called for macvtap does not have any >> synchronization. >> >> Fix this by forbidding L2 forwarding for macvtap. >> >> Cc: John Fastabend <john.r.fastabend@intel.com> >> Cc: Neil Horman <nhorman@tuxdriver.com> >> Signed-off-by: Jason Wang <jasowang@redhat.com> >> --- >> drivers/net/macvlan.c | 5 ++++- >> 1 files changed, 4 insertions(+), 1 deletions(-) >> > > I must be missing something. > > The lower layer device should set skb->dev to the correct macvtap > device on receive so that in netif_receive_skb_core() the macvtap > handler is hit. Skipping the macvlan receive handler should be OK > because the switching was done by the hardware. If I read macvtap.c > correctly macvlan_common_newlink() is called with 'dev' where 'dev' > is the macvtap device. Any idea what I'm missing? I guess I'll need > to setup a macvtap test case. Unlike macvlan, macvtap depends on rx handler on the lower device to work. In this case macvlan_handle_frame() will call macvtap_receive(). So doing netif_receive_skb_core() for macvtap device directly won't work since we need to forward the packet to userspace instead of kernel. For net-next.git, it may work since commit 6acf54f1cf0a6747bac9fea26f34cfc5a9029523 let macvtap device register an rx handler for itself. > > And what synchronization are you worried about on dev_hard_start_xmit()? > In the L2 forwarding offload case macvlan_open() clears the NETIF_F_LLTX > flag so HARD_TX_LOCK protects the driver txq. We might hit this warning > in dev_queue_xmit() though, > > net_crit_ratelimited("Virtual device %s asks to queue packet!\n", > > Perhaps we can remove it. The problem is macvtap does not call dev_queue_xmit() for macvlan device. It calls macvlan_start_xmit() directly from macvtap_get_user(). So HARD_TX_LOCK was not done for the txq. > >> diff --git a/drivers/net/macvlan.c b/drivers/net/macvlan.c >> index 60406b0..5360f73 100644 >> --- a/drivers/net/macvlan.c >> +++ b/drivers/net/macvlan.c >> @@ -338,6 +338,8 @@ static const struct header_ops >> macvlan_hard_header_ops = { >> .cache_update = eth_header_cache_update, >> }; >> >> +static struct rtnl_link_ops macvlan_link_ops; >> + >> static int macvlan_open(struct net_device *dev) >> { >> struct macvlan_dev *vlan = netdev_priv(dev); >> @@ -353,7 +355,8 @@ static int macvlan_open(struct net_device *dev) >> goto hash_add; >> } >> >> - if (lowerdev->features & NETIF_F_HW_L2FW_DOFFLOAD) { >> + if (lowerdev->features & NETIF_F_HW_L2FW_DOFFLOAD && >> + dev->rtnl_link_ops == &macvlan_link_ops) { >> vlan->fwd_priv = >> lowerdev->netdev_ops->ndo_dfwd_add_station(lowerdev, >> dev); >> >> > > -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Mon, Jan 06, 2014 at 03:54:21PM +0800, Jason Wang wrote: > On 01/06/2014 03:35 PM, John Fastabend wrote: > > On 01/05/2014 07:21 PM, Jason Wang wrote: > >> L2 fowarding offload will bypass the rx handler of real device. This > >> will make > >> the packet could not be forwarded to macvtap device. Another problem > >> is the > >> dev_hard_start_xmit() called for macvtap does not have any > >> synchronization. > >> > >> Fix this by forbidding L2 forwarding for macvtap. > >> > >> Cc: John Fastabend <john.r.fastabend@intel.com> > >> Cc: Neil Horman <nhorman@tuxdriver.com> > >> Signed-off-by: Jason Wang <jasowang@redhat.com> > >> --- > >> drivers/net/macvlan.c | 5 ++++- > >> 1 files changed, 4 insertions(+), 1 deletions(-) > >> > > > > I must be missing something. > > > > The lower layer device should set skb->dev to the correct macvtap > > device on receive so that in netif_receive_skb_core() the macvtap > > handler is hit. Skipping the macvlan receive handler should be OK > > because the switching was done by the hardware. If I read macvtap.c > > correctly macvlan_common_newlink() is called with 'dev' where 'dev' > > is the macvtap device. Any idea what I'm missing? I guess I'll need > > to setup a macvtap test case. > > Unlike macvlan, macvtap depends on rx handler on the lower device to > work. In this case macvlan_handle_frame() will call macvtap_receive(). > So doing netif_receive_skb_core() for macvtap device directly won't work > since we need to forward the packet to userspace instead of kernel. > > For net-next.git, it may work since commit > 6acf54f1cf0a6747bac9fea26f34cfc5a9029523 let macvtap device register an > rx handler for itself. I agree, this seems like it should already be fixed with the above commit. With this the macvlan rx handler should effectively be a no-op as far as the reception of frames is concerned. As long as the driver sets the dev correctly to the macvtap device (and it appears to), macvtap will get frames to user space, regardless of weather the software or hardware did the switching. If thats the case though, I think the solution is moving that fix to -stable (pending testing of course), rather than comming up with a new fix. > > > > And what synchronization are you worried about on dev_hard_start_xmit()? > > In the L2 forwarding offload case macvlan_open() clears the NETIF_F_LLTX > > flag so HARD_TX_LOCK protects the driver txq. We might hit this warning > > in dev_queue_xmit() though, > > > > net_crit_ratelimited("Virtual device %s asks to queue packet!\n", > > > > Perhaps we can remove it. > > The problem is macvtap does not call dev_queue_xmit() for macvlan > device. It calls macvlan_start_xmit() directly from macvtap_get_user(). > So HARD_TX_LOCK was not done for the txq. This seems to also be fixed by 6acf54f1cf0a6747bac9fea26f34cfc5a9029523. Macvtap does, as of that commit use dev_queue_xmit for the transmission of frames to the lowerdevice. Regards Neil -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
From: Jason Wang <jasowang@redhat.com> Date: Mon, 6 Jan 2014 11:21:06 +0800 > L2 fowarding offload will bypass the rx handler of real device. This will make > the packet could not be forwarded to macvtap device. Another problem is the > dev_hard_start_xmit() called for macvtap does not have any synchronization. > > Fix this by forbidding L2 forwarding for macvtap. > > Cc: John Fastabend <john.r.fastabend@intel.com> > Cc: Neil Horman <nhorman@tuxdriver.com> > Signed-off-by: Jason Wang <jasowang@redhat.com> I think I agree with Neil that the rx_handler change might be the best way to fix this. That change seems to have a lot of nice unintended side effects, no? -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 01/06/2014 08:26 PM, Neil Horman wrote: > On Mon, Jan 06, 2014 at 03:54:21PM +0800, Jason Wang wrote: >> On 01/06/2014 03:35 PM, John Fastabend wrote: >>> On 01/05/2014 07:21 PM, Jason Wang wrote: >>>> L2 fowarding offload will bypass the rx handler of real device. This >>>> will make >>>> the packet could not be forwarded to macvtap device. Another problem >>>> is the >>>> dev_hard_start_xmit() called for macvtap does not have any >>>> synchronization. >>>> >>>> Fix this by forbidding L2 forwarding for macvtap. >>>> >>>> Cc: John Fastabend <john.r.fastabend@intel.com> >>>> Cc: Neil Horman <nhorman@tuxdriver.com> >>>> Signed-off-by: Jason Wang <jasowang@redhat.com> >>>> --- >>>> drivers/net/macvlan.c | 5 ++++- >>>> 1 files changed, 4 insertions(+), 1 deletions(-) >>>> >>> I must be missing something. >>> >>> The lower layer device should set skb->dev to the correct macvtap >>> device on receive so that in netif_receive_skb_core() the macvtap >>> handler is hit. Skipping the macvlan receive handler should be OK >>> because the switching was done by the hardware. If I read macvtap.c >>> correctly macvlan_common_newlink() is called with 'dev' where 'dev' >>> is the macvtap device. Any idea what I'm missing? I guess I'll need >>> to setup a macvtap test case. >> Unlike macvlan, macvtap depends on rx handler on the lower device to >> work. In this case macvlan_handle_frame() will call macvtap_receive(). >> So doing netif_receive_skb_core() for macvtap device directly won't work >> since we need to forward the packet to userspace instead of kernel. >> >> For net-next.git, it may work since commit >> 6acf54f1cf0a6747bac9fea26f34cfc5a9029523 let macvtap device register an >> rx handler for itself. > I agree, this seems like it should already be fixed with the above commit. With > this the macvlan rx handler should effectively be a no-op as far as the > reception of frames is concerned. As long as the driver sets the dev correctly > to the macvtap device (and it appears to), macvtap will get frames to user > space, regardless of weather the software or hardware did the switching. If > thats the case though, I think the solution is moving that fix to -stable > (pending testing of course), rather than comming up with a new fix. > >>> And what synchronization are you worried about on dev_hard_start_xmit()? >>> In the L2 forwarding offload case macvlan_open() clears the NETIF_F_LLTX >>> flag so HARD_TX_LOCK protects the driver txq. We might hit this warning >>> in dev_queue_xmit() though, >>> >>> net_crit_ratelimited("Virtual device %s asks to queue packet!\n", >>> >>> Perhaps we can remove it. >> The problem is macvtap does not call dev_queue_xmit() for macvlan >> device. It calls macvlan_start_xmit() directly from macvtap_get_user(). >> So HARD_TX_LOCK was not done for the txq. > This seems to also be fixed by 6acf54f1cf0a6747bac9fea26f34cfc5a9029523. > Macvtap does, as of that commit use dev_queue_xmit for the transmission of > frames to the lowerdevice. Unfortunately not. This commit has a side effect that it in fact disables the multiqueue macvtap transmission. Since all macvtap queues will contend on a single qdisc lock. For L2 forwarding offload itself, more issues need to be addressed for multiqueue macvtap: - ndo_dfwd_add_station() can only create queues per device at ndo_open, but multiqueue macvtap allows user to create and destroy queues at their will and at any time. - it looks that ixgbe has a upper limit of 4 queues per station, but macvtap currently allows up to 16 queues per device. So more works need to be done and unless those above 3 issues were addressed, this patch is really needed to make sure macvtap works. > > Regards > Neil > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 01/07/2014 04:47 AM, David Miller wrote: > From: Jason Wang <jasowang@redhat.com> > Date: Mon, 6 Jan 2014 11:21:06 +0800 > >> L2 fowarding offload will bypass the rx handler of real device. This will make >> the packet could not be forwarded to macvtap device. Another problem is the >> dev_hard_start_xmit() called for macvtap does not have any synchronization. >> >> Fix this by forbidding L2 forwarding for macvtap. >> >> Cc: John Fastabend <john.r.fastabend@intel.com> >> Cc: Neil Horman <nhorman@tuxdriver.com> >> Signed-off-by: Jason Wang <jasowang@redhat.com> > I think I agree with Neil that the rx_handler change might be the best > way to fix this. That change seems to have a lot of nice unintended > side effects, no? Not all sides effects are nice. One obvious issue is it disables the multiqueue macvtap transmission, since all queues will contend on a single qdisc lock of macvlan. And even more, multiqueue macvtap support creating and destroying a queue on demand which is not supported by L2 forwarding offload. So L2 forwarding offload needs more fixes to let the multiqueue macvtap works. Currently, we really need this patch to make sure macvtap works as expected. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 01/06/2014 07:10 PM, Jason Wang wrote: > On 01/06/2014 08:26 PM, Neil Horman wrote: >> On Mon, Jan 06, 2014 at 03:54:21PM +0800, Jason Wang wrote: >>> On 01/06/2014 03:35 PM, John Fastabend wrote: >>>> On 01/05/2014 07:21 PM, Jason Wang wrote: >>>>> L2 fowarding offload will bypass the rx handler of real device. This >>>>> will make >>>>> the packet could not be forwarded to macvtap device. Another problem >>>>> is the >>>>> dev_hard_start_xmit() called for macvtap does not have any >>>>> synchronization. >>>>> >>>>> Fix this by forbidding L2 forwarding for macvtap. >>>>> >>>>> Cc: John Fastabend <john.r.fastabend@intel.com> >>>>> Cc: Neil Horman <nhorman@tuxdriver.com> >>>>> Signed-off-by: Jason Wang <jasowang@redhat.com> >>>>> --- >>>>> drivers/net/macvlan.c | 5 ++++- >>>>> 1 files changed, 4 insertions(+), 1 deletions(-) >>>>> >>>> I must be missing something. >>>> >>>> The lower layer device should set skb->dev to the correct macvtap >>>> device on receive so that in netif_receive_skb_core() the macvtap >>>> handler is hit. Skipping the macvlan receive handler should be OK >>>> because the switching was done by the hardware. If I read macvtap.c >>>> correctly macvlan_common_newlink() is called with 'dev' where 'dev' >>>> is the macvtap device. Any idea what I'm missing? I guess I'll need >>>> to setup a macvtap test case. >>> Unlike macvlan, macvtap depends on rx handler on the lower device to >>> work. In this case macvlan_handle_frame() will call macvtap_receive(). >>> So doing netif_receive_skb_core() for macvtap device directly won't work >>> since we need to forward the packet to userspace instead of kernel. >>> >>> For net-next.git, it may work since commit >>> 6acf54f1cf0a6747bac9fea26f34cfc5a9029523 let macvtap device register an >>> rx handler for itself. >> I agree, this seems like it should already be fixed with the above commit. With >> this the macvlan rx handler should effectively be a no-op as far as the >> reception of frames is concerned. As long as the driver sets the dev correctly >> to the macvtap device (and it appears to), macvtap will get frames to user >> space, regardless of weather the software or hardware did the switching. If >> thats the case though, I think the solution is moving that fix to -stable >> (pending testing of course), rather than comming up with a new fix. >> >>>> And what synchronization are you worried about on dev_hard_start_xmit()? >>>> In the L2 forwarding offload case macvlan_open() clears the NETIF_F_LLTX >>>> flag so HARD_TX_LOCK protects the driver txq. We might hit this warning >>>> in dev_queue_xmit() though, >>>> >>>> net_crit_ratelimited("Virtual device %s asks to queue packet!\n", >>>> >>>> Perhaps we can remove it. >>> The problem is macvtap does not call dev_queue_xmit() for macvlan >>> device. It calls macvlan_start_xmit() directly from macvtap_get_user(). >>> So HARD_TX_LOCK was not done for the txq. >> This seems to also be fixed by 6acf54f1cf0a6747bac9fea26f34cfc5a9029523. >> Macvtap does, as of that commit use dev_queue_xmit for the transmission of >> frames to the lowerdevice. > > Unfortunately not. This commit has a side effect that it in fact > disables the multiqueue macvtap transmission. Since all macvtap queues > will contend on a single qdisc lock. > They will only contend on a single qdisc lock if the lower device has 1 queue. Perhaps defaulting the L2 forwarding devices to 1queue was a mistake. But the same issue arises when running macvtap over a non-multiqueue nic. Or even if you have a multiqueue device and create many more macvtap queues than the lower device has queues. Shouldn't the macvtap configuration take into account the lowest level devices queues? How does using the L2 forwarding device change the contention issues? Without the L2 forwarding LLTX is enabled but the qdisc lock, etc is still acquired on the device below the macvlan. The ixgbe driver as it is currently written can be configured for up to 4 queues by setting numtxqueues when the device is created. I assume when creating macvtap queues the user needs to account for the number of queues supported by the lower device. > For L2 forwarding offload itself, more issues need to be addressed for > multiqueue macvtap: > > - ndo_dfwd_add_station() can only create queues per device at ndo_open, > but multiqueue macvtap allows user to create and destroy queues at their > will and at any time. same argument as above, isn't this the same when running macvtap without the l2 offloads over a real device? I expect you hit the same contention points when running over a real device. > - it looks that ixgbe has a upper limit of 4 queues per station, but > macvtap currently allows up to 16 queues per device. > The 4 limit was to simplify the code because the queue mapping in the driver gets complicated if it is greater than 4. We can probably increase this latter. But sorry reiterating how is this different than a macvtap on a real device that supports a max of 4 queues? > So more works need to be done and unless those above 3 issues were > addressed, this patch is really needed to make sure macvtap works. > Agreed there is a lot more work here to improve things I'm just not sure we need to disable this now. Also note its the l2 forwarding should be disabled by default so a user would have to enable the feature flag. Thanks, John
On 01/06/2014 07:10 PM, Jason Wang wrote: > On 01/06/2014 08:26 PM, Neil Horman wrote: >> On Mon, Jan 06, 2014 at 03:54:21PM +0800, Jason Wang wrote: >>> On 01/06/2014 03:35 PM, John Fastabend wrote: >>>> On 01/05/2014 07:21 PM, Jason Wang wrote: >>>>> L2 fowarding offload will bypass the rx handler of real device. This >>>>> will make >>>>> the packet could not be forwarded to macvtap device. Another problem >>>>> is the >>>>> dev_hard_start_xmit() called for macvtap does not have any >>>>> synchronization. >>>>> >>>>> Fix this by forbidding L2 forwarding for macvtap. >>>>> >>>>> Cc: John Fastabend <john.r.fastabend@intel.com> >>>>> Cc: Neil Horman <nhorman@tuxdriver.com> >>>>> Signed-off-by: Jason Wang <jasowang@redhat.com> >>>>> --- >>>>> drivers/net/macvlan.c | 5 ++++- >>>>> 1 files changed, 4 insertions(+), 1 deletions(-) >>>>> >>>> I must be missing something. >>>> >>>> The lower layer device should set skb->dev to the correct macvtap >>>> device on receive so that in netif_receive_skb_core() the macvtap >>>> handler is hit. Skipping the macvlan receive handler should be OK >>>> because the switching was done by the hardware. If I read macvtap.c >>>> correctly macvlan_common_newlink() is called with 'dev' where 'dev' >>>> is the macvtap device. Any idea what I'm missing? I guess I'll need >>>> to setup a macvtap test case. >>> Unlike macvlan, macvtap depends on rx handler on the lower device to >>> work. In this case macvlan_handle_frame() will call macvtap_receive(). >>> So doing netif_receive_skb_core() for macvtap device directly won't work >>> since we need to forward the packet to userspace instead of kernel. >>> >>> For net-next.git, it may work since commit >>> 6acf54f1cf0a6747bac9fea26f34cfc5a9029523 let macvtap device register an >>> rx handler for itself. >> I agree, this seems like it should already be fixed with the above commit. With >> this the macvlan rx handler should effectively be a no-op as far as the >> reception of frames is concerned. As long as the driver sets the dev correctly >> to the macvtap device (and it appears to), macvtap will get frames to user >> space, regardless of weather the software or hardware did the switching. If >> thats the case though, I think the solution is moving that fix to -stable >> (pending testing of course), rather than comming up with a new fix. >> >>>> And what synchronization are you worried about on dev_hard_start_xmit()? >>>> In the L2 forwarding offload case macvlan_open() clears the NETIF_F_LLTX >>>> flag so HARD_TX_LOCK protects the driver txq. We might hit this warning >>>> in dev_queue_xmit() though, >>>> >>>> net_crit_ratelimited("Virtual device %s asks to queue packet!\n", >>>> >>>> Perhaps we can remove it. >>> The problem is macvtap does not call dev_queue_xmit() for macvlan >>> device. It calls macvlan_start_xmit() directly from macvtap_get_user(). >>> So HARD_TX_LOCK was not done for the txq. >> This seems to also be fixed by 6acf54f1cf0a6747bac9fea26f34cfc5a9029523. >> Macvtap does, as of that commit use dev_queue_xmit for the transmission of >> frames to the lowerdevice. > > Unfortunately not. This commit has a side effect that it in fact > disables the multiqueue macvtap transmission. Since all macvtap queues > will contend on a single qdisc lock. > They will only contend on a single qdisc lock if the lower device has 1 queue. Perhaps defaulting the L2 forwarding devices to 1queue was a mistake. But the same issue arises when running macvtap over a non-multiqueue nic. Or even if you have a multiqueue device and create many more macvtap queues than the lower device has queues. Shouldn't the macvtap configuration take into account the lowest level devices queues? How does using the L2 forwarding device change the contention issues? Without the L2 forwarding LLTX is enabled but the qdisc lock, etc is still acquired on the device below the macvlan. The ixgbe driver as it is currently written can be configured for up to 4 queues by setting numtxqueues when the device is created. I assume when creating macvtap queues the user needs to account for the number of queues supported by the lower device. > For L2 forwarding offload itself, more issues need to be addressed for > multiqueue macvtap: > > - ndo_dfwd_add_station() can only create queues per device at ndo_open, > but multiqueue macvtap allows user to create and destroy queues at their > will and at any time. same argument as above, isn't this the same when running macvtap without the l2 offloads over a real device? I expect you hit the same contention points when running over a real device. > - it looks that ixgbe has a upper limit of 4 queues per station, but > macvtap currently allows up to 16 queues per device. > The 4 limit was to simplify the code because the queue mapping in the driver gets complicated if it is greater than 4. We can probably increase this latter. But sorry reiterating how is this different than a macvtap on a real device that supports a max of 4 queues? > So more works need to be done and unless those above 3 issues were > addressed, this patch is really needed to make sure macvtap works. > Agreed there is a lot more work here to improve things I'm just not sure we need to disable this now. Also note its the l2 forwarding should be disabled by default so a user would have to enable the feature flag. Thanks, John
From: Jason Wang <jasowang@redhat.com> Date: Tue, 07 Jan 2014 11:17:06 +0800 > On 01/07/2014 04:47 AM, David Miller wrote: >> From: Jason Wang <jasowang@redhat.com> >> Date: Mon, 6 Jan 2014 11:21:06 +0800 >> >>> L2 fowarding offload will bypass the rx handler of real device. This will make >>> the packet could not be forwarded to macvtap device. Another problem is the >>> dev_hard_start_xmit() called for macvtap does not have any synchronization. >>> >>> Fix this by forbidding L2 forwarding for macvtap. >>> >>> Cc: John Fastabend <john.r.fastabend@intel.com> >>> Cc: Neil Horman <nhorman@tuxdriver.com> >>> Signed-off-by: Jason Wang <jasowang@redhat.com> >> I think I agree with Neil that the rx_handler change might be the best >> way to fix this. That change seems to have a lot of nice unintended >> side effects, no? > > Not all sides effects are nice. > > One obvious issue is it disables the multiqueue macvtap transmission, > since all queues will contend on a single qdisc lock of macvlan. And > even more, multiqueue macvtap support creating and destroying a queue on > demand which is not supported by L2 forwarding offload. > > So L2 forwarding offload needs more fixes to let the multiqueue macvtap > works. Currently, we really need this patch to make sure macvtap works > as expected. Ok I moved these two patches back to "Under Review". These are pretty last minute and we'll need to make a decision on what to do before Friday if you want these changes to really make it into 3.13 -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 01/07/2014 01:15 PM, John Fastabend wrote: > On 01/06/2014 07:10 PM, Jason Wang wrote: >> On 01/06/2014 08:26 PM, Neil Horman wrote: >>> On Mon, Jan 06, 2014 at 03:54:21PM +0800, Jason Wang wrote: >>>> On 01/06/2014 03:35 PM, John Fastabend wrote: >>>>> On 01/05/2014 07:21 PM, Jason Wang wrote: >>>>>> L2 fowarding offload will bypass the rx handler of real device. This >>>>>> will make >>>>>> the packet could not be forwarded to macvtap device. Another problem >>>>>> is the >>>>>> dev_hard_start_xmit() called for macvtap does not have any >>>>>> synchronization. >>>>>> >>>>>> Fix this by forbidding L2 forwarding for macvtap. >>>>>> >>>>>> Cc: John Fastabend <john.r.fastabend@intel.com> >>>>>> Cc: Neil Horman <nhorman@tuxdriver.com> >>>>>> Signed-off-by: Jason Wang <jasowang@redhat.com> >>>>>> --- >>>>>> drivers/net/macvlan.c | 5 ++++- >>>>>> 1 files changed, 4 insertions(+), 1 deletions(-) >>>>>> >>>>> I must be missing something. >>>>> >>>>> The lower layer device should set skb->dev to the correct macvtap >>>>> device on receive so that in netif_receive_skb_core() the macvtap >>>>> handler is hit. Skipping the macvlan receive handler should be OK >>>>> because the switching was done by the hardware. If I read macvtap.c >>>>> correctly macvlan_common_newlink() is called with 'dev' where 'dev' >>>>> is the macvtap device. Any idea what I'm missing? I guess I'll need >>>>> to setup a macvtap test case. >>>> Unlike macvlan, macvtap depends on rx handler on the lower device to >>>> work. In this case macvlan_handle_frame() will call macvtap_receive(). >>>> So doing netif_receive_skb_core() for macvtap device directly won't >>>> work >>>> since we need to forward the packet to userspace instead of kernel. >>>> >>>> For net-next.git, it may work since commit >>>> 6acf54f1cf0a6747bac9fea26f34cfc5a9029523 let macvtap device >>>> register an >>>> rx handler for itself. >>> I agree, this seems like it should already be fixed with the above >>> commit. With >>> this the macvlan rx handler should effectively be a no-op as far as the >>> reception of frames is concerned. As long as the driver sets the >>> dev correctly >>> to the macvtap device (and it appears to), macvtap will get frames >>> to user >>> space, regardless of weather the software or hardware did the >>> switching. If >>> thats the case though, I think the solution is moving that fix to >>> -stable >>> (pending testing of course), rather than comming up with a new fix. >>> >>>>> And what synchronization are you worried about on >>>>> dev_hard_start_xmit()? >>>>> In the L2 forwarding offload case macvlan_open() clears the >>>>> NETIF_F_LLTX >>>>> flag so HARD_TX_LOCK protects the driver txq. We might hit this >>>>> warning >>>>> in dev_queue_xmit() though, >>>>> >>>>> net_crit_ratelimited("Virtual device %s asks to queue packet!\n", >>>>> >>>>> Perhaps we can remove it. >>>> The problem is macvtap does not call dev_queue_xmit() for macvlan >>>> device. It calls macvlan_start_xmit() directly from >>>> macvtap_get_user(). >>>> So HARD_TX_LOCK was not done for the txq. >>> This seems to also be fixed by >>> 6acf54f1cf0a6747bac9fea26f34cfc5a9029523. >>> Macvtap does, as of that commit use dev_queue_xmit for the >>> transmission of >>> frames to the lowerdevice. >> >> Unfortunately not. This commit has a side effect that it in fact >> disables the multiqueue macvtap transmission. Since all macvtap queues >> will contend on a single qdisc lock. >> > > They will only contend on a single qdisc lock if the lower device has > 1 queue. I think we are talking about 6acf54f1cf0a6747bac9fea26f34cfc5a9029523. The qdisc or txq lock were macvlan device itself since dev_queue_xmit() was called for macvlan device itself. So even if lower device has multiple txqs, if you just create a one queue macvlan device, you will get lock contention on macvlan device. And even if you explicitly specifying the txq numbers ( though I don't believe most management software will do this) when creating the macvlan/macvtap device, you must also configure the XPS for macvlan to make sure it has the possibility of using multiple transmit queues. > Perhaps defaulting the L2 forwarding devices to 1queue was a > mistake. But the same issue arises when running macvtap over a > non-multiqueue nic. Or even if you have a multiqueue device and create > many more macvtap queues than the lower device has queues. > > Shouldn't the macvtap configuration take into account the lowest level > devices queues? See commit 8ffab51b3dfc54876f145f15b351c41f3f703195 ("macvlan: lockless tx path"). It allows the management to create a device without worrying the underlying device. > How does using the L2 forwarding device change the > contention issues? Without the L2 forwarding LLTX is enabled but the > qdisc lock, etc is still acquired on the device below the macvlan. > That's the point. We need make sure the txq selection and qdisc lock were done for the lower device not for the macvlan device itself. Then macvlan can automatically benefit from the multi-queue capable lower devices. But L2 forwarding needs to contend on the txq lock on macvlan device itself, which is unnecessary and can complex the management. > The ixgbe driver as it is currently written can be configured for up to > 4 queues by setting numtxqueues when the device is created. I assume > when creating macvtap queues the user needs to account for the number > of queues supported by the lower device. > We'd better not complicate the task of management, lockless tx path work very well so we can just keep it. Btw, there's no way for the user to know the maximum number of queues that L2 forwarding supports. >> For L2 forwarding offload itself, more issues need to be addressed for >> multiqueue macvtap: >> >> - ndo_dfwd_add_station() can only create queues per device at ndo_open, >> but multiqueue macvtap allows user to create and destroy queues at their >> will and at any time. > > same argument as above, isn't this the same when running macvtap without > the l2 offloads over a real device? I expect you hit the same contention > points when running over a real device. Not true and not only for contention. Macvtap allows user to create or destroy a queue by simply open or close to character device /dev/tapX. But currently, we do nothing when a new queue was created or destroyed for L2 forwarding offload. For contention, lockless tx path make the contention only happens for the txq or qdisc for the lower device, but L2 forwarding offload make contention also happen for the macvlan device itself. > > >> - it looks that ixgbe has a upper limit of 4 queues per station, but >> macvtap currently allows up to 16 queues per device. >> > > The 4 limit was to simplify the code because the queue mapping in the > driver gets complicated if it is greater than 4. We can probably > increase this latter. But sorry reiterating how is this different than > a macvtap on a real device that supports a max of 4 queues? Well, it maybe easy. I just point out possible issues we may meet currently. > >> So more works need to be done and unless those above 3 issues were >> addressed, this patch is really needed to make sure macvtap works. >> > > Agreed there is a lot more work here to improve things I'm just not > sure we need to disable this now. Also note its the l2 forwarding > should be disabled by default so a user would have to enable the > feature flag. Even if it was disabled by default. We should not surprise the user who want to enable it for macvtap. > > Thanks, > John > Thanks -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[...] >>> Unfortunately not. This commit has a side effect that it in fact >>> disables the multiqueue macvtap transmission. Since all macvtap queues >>> will contend on a single qdisc lock. >>> >> >> They will only contend on a single qdisc lock if the lower device has >> 1 queue. > > I think we are talking about 6acf54f1cf0a6747bac9fea26f34cfc5a9029523. Yes. > > The qdisc or txq lock were macvlan device itself since dev_queue_xmit() > was called for macvlan device itself. So even if lower device has > multiple txqs, if you just create a one queue macvlan device, you will > get lock contention on macvlan device. And even if you explicitly > specifying the txq numbers ( though I don't believe most management > software will do this) when creating the macvlan/macvtap device, you > must also configure the XPS for macvlan to make sure it has the > possibility of using multiple transmit queues. > OK I think I'm finally putting all the pieces together thanks. Do you know why macvtap is setting dev->tx_queue_len by default? If you zero this then the noqueue_qdisc is used and the q->enqueue check in dev_queue_xmit will fail. Also if XPS is not configured then skb_tx_hash is used so multiple transmit queues will still be used. >> Perhaps defaulting the L2 forwarding devices to 1queue was a >> mistake. But the same issue arises when running macvtap over a >> non-multiqueue nic. Or even if you have a multiqueue device and create >> many more macvtap queues than the lower device has queues. >> >> Shouldn't the macvtap configuration take into account the lowest level >> devices queues? > > See commit 8ffab51b3dfc54876f145f15b351c41f3f703195 ("macvlan: lockless > tx path"). It allows the management to create a device without worrying > the underlying device. OK. >> How does using the L2 forwarding device change the >> contention issues? Without the L2 forwarding LLTX is enabled but the >> qdisc lock, etc is still acquired on the device below the macvlan. >> > > That's the point. We need make sure the txq selection and qdisc lock > were done for the lower device not for the macvlan device itself. Then > macvlan can automatically benefit from the multi-queue capable lower > devices. But L2 forwarding needs to contend on the txq lock on macvlan > device itself, which is unnecessary and can complex the management. If I make the l2 forwarding defaults a bit better then using the L2 forwarding case should not be any more complex. And because the queues are dedicated to the macvtap device any contention from qdisc lock, etc comes from the upper device only. Also if I get the bandwidth controls in we can set the max/min bandwidth per macvtap device this way. That is future work though. >> The ixgbe driver as it is currently written can be configured for up to >> 4 queues by setting numtxqueues when the device is created. I assume >> when creating macvtap queues the user needs to account for the number >> of queues supported by the lower device. >> > > We'd better not complicate the task of management, lockless tx path work > very well so we can just keep it. Btw, there's no way for the user to > know the maximum number of queues that L2 forwarding supports. Good point I'll add an attribute to query it. >>> For L2 forwarding offload itself, more issues need to be addressed for >>> multiqueue macvtap: >>> >>> - ndo_dfwd_add_station() can only create queues per device at ndo_open, >>> but multiqueue macvtap allows user to create and destroy queues at their >>> will and at any time. >> >> same argument as above, isn't this the same when running macvtap without >> the l2 offloads over a real device? I expect you hit the same contention >> points when running over a real device. > > Not true and not only for contention. > > Macvtap allows user to create or destroy a queue by simply open or close > to character device /dev/tapX. But currently, we do nothing when a new > queue was created or destroyed for L2 forwarding offload. > > For contention, lockless tx path make the contention only happens for > the txq or qdisc for the lower device, but L2 forwarding offload make > contention also happen for the macvlan device itself. Right, but there will be less contention there because those queues are a dedicated resource for the upper device. At this point I think I need to put together a real testbed and benchmark some of this with netperf and perf running to get real numbers. When I originally did the l2 forwarding I did not do any testing with multiple macvtap queues and only very limited work with macvtap. > >> >> >>> - it looks that ixgbe has a upper limit of 4 queues per station, but >>> macvtap currently allows up to 16 queues per device. >>> >> >> The 4 limit was to simplify the code because the queue mapping in the >> driver gets complicated if it is greater than 4. We can probably >> increase this latter. But sorry reiterating how is this different than >> a macvtap on a real device that supports a max of 4 queues? > > Well, it maybe easy. I just point out possible issues we may meet currently. Right. >> >>> So more works need to be done and unless those above 3 issues were >>> addressed, this patch is really needed to make sure macvtap works. >>> >> >> Agreed there is a lot more work here to improve things I'm just not >> sure we need to disable this now. Also note its the l2 forwarding >> should be disabled by default so a user would have to enable the >> feature flag. > > Even if it was disabled by default. We should not surprise the user who > want to enable it for macvtap. So the question is what to do in net while we improve net-next. Either we fix the crash from the null txq and note that with l2 forwarding some non default configuration is needed for optimal performance OR for now disable it as your patch does. I would prefer to fix the crash and note the configuration but I see your point about surprising users so could go either way. Neil any thoughts? To fix the null txq in the gso case adding a check for a non-null txq before calling txq_trans_update() makes sense to me. We already have the check in the non-gso case so making it symmetric fixes it. >> >> Thanks, >> John >> > > Thanks > -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 01/07/2014 03:26 PM, John Fastabend wrote: > [...] > >>>> Unfortunately not. This commit has a side effect that it in fact >>>> disables the multiqueue macvtap transmission. Since all macvtap queues >>>> will contend on a single qdisc lock. >>>> >>> >>> They will only contend on a single qdisc lock if the lower device has >>> 1 queue. >> >> I think we are talking about 6acf54f1cf0a6747bac9fea26f34cfc5a9029523. > > Yes. > >> >> The qdisc or txq lock were macvlan device itself since dev_queue_xmit() >> was called for macvlan device itself. So even if lower device has >> multiple txqs, if you just create a one queue macvlan device, you will >> get lock contention on macvlan device. And even if you explicitly >> specifying the txq numbers ( though I don't believe most management >> software will do this) when creating the macvlan/macvtap device, you >> must also configure the XPS for macvlan to make sure it has the >> possibility of using multiple transmit queues. >> > > OK I think I'm finally putting all the pieces together thanks. > > Do you know why macvtap is setting dev->tx_queue_len by default? If you > zero this then the noqueue_qdisc is used and the q->enqueue check in > dev_queue_xmit will fail. It was introduced in commit 8a35747a5d13b99e076b0222729e0caa48cb69b6 ("macvtap: Limit packet queue length") to limit the length of socket receive queue of macvtap. But I'm not sure whether the qdisc is a byproduct of this commit, maybe we can switch to use another name instead of just reuse dev->tx_queue_length. > > Also if XPS is not configured then skb_tx_hash is used so multiple > transmit queues will still be used. > True. >>> Perhaps defaulting the L2 forwarding devices to 1queue was a >>> mistake. But the same issue arises when running macvtap over a >>> non-multiqueue nic. Or even if you have a multiqueue device and create >>> many more macvtap queues than the lower device has queues. >>> >>> Shouldn't the macvtap configuration take into account the lowest level >>> devices queues? >> >> See commit 8ffab51b3dfc54876f145f15b351c41f3f703195 ("macvlan: lockless >> tx path"). It allows the management to create a device without worrying >> the underlying device. > > OK. > >>> How does using the L2 forwarding device change the >>> contention issues? Without the L2 forwarding LLTX is enabled but the >>> qdisc lock, etc is still acquired on the device below the macvlan. >>> >> >> That's the point. We need make sure the txq selection and qdisc lock >> were done for the lower device not for the macvlan device itself. Then >> macvlan can automatically benefit from the multi-queue capable lower >> devices. But L2 forwarding needs to contend on the txq lock on macvlan >> device itself, which is unnecessary and can complex the management. > > If I make the l2 forwarding defaults a bit better then using the L2 > forwarding case should not be any more complex. And because the queues > are dedicated to the macvtap device any contention from qdisc lock, etc > comes from the upper device only. At very least the txq of lower device should be held in order to be synchronized with management path. Consider txq lock were often held by netif_tx_disable() before trying to down the card. Current cold does not hold txq lock, so it loses the synchronization which may cause issues. And the code also does not check whether the txq has been stopped before trying to start the transmission. > Also if I get the bandwidth controls > in we can set the max/min bandwidth per macvtap device this way. That > is future work though. > That will be a nice feature. >>> The ixgbe driver as it is currently written can be configured for up to >>> 4 queues by setting numtxqueues when the device is created. I assume >>> when creating macvtap queues the user needs to account for the number >>> of queues supported by the lower device. >>> >> >> We'd better not complicate the task of management, lockless tx path work >> very well so we can just keep it. Btw, there's no way for the user to >> know the maximum number of queues that L2 forwarding supports. > > Good point I'll add an attribute to query it. > >>>> For L2 forwarding offload itself, more issues need to be addressed for >>>> multiqueue macvtap: >>>> >>>> - ndo_dfwd_add_station() can only create queues per device at >>>> ndo_open, >>>> but multiqueue macvtap allows user to create and destroy queues at >>>> their >>>> will and at any time. >>> >>> same argument as above, isn't this the same when running macvtap >>> without >>> the l2 offloads over a real device? I expect you hit the same >>> contention >>> points when running over a real device. >> >> Not true and not only for contention. >> >> Macvtap allows user to create or destroy a queue by simply open or close >> to character device /dev/tapX. But currently, we do nothing when a new >> queue was created or destroyed for L2 forwarding offload. >> >> For contention, lockless tx path make the contention only happens for >> the txq or qdisc for the lower device, but L2 forwarding offload make >> contention also happen for the macvlan device itself. > > Right, but there will be less contention there because those queues > are a dedicated resource for the upper device. Yes and this is also true if we only do synchronization on the lower device since only dedicated queues could be selected. > > At this point I think I need to put together a real testbed and > benchmark some of this with netperf and perf running to get real > numbers. When I originally did the l2 forwarding I did not do any > testing with multiple macvtap queues and only very limited work with > macvtap. > As I said above, holding the txq lock of lower device seems a must and we should not get regression if NETIF_F_LLTX is kept. But I agree we need some test. >> >>> >>> >>>> - it looks that ixgbe has a upper limit of 4 queues per station, but >>>> macvtap currently allows up to 16 queues per device. >>>> >>> >>> The 4 limit was to simplify the code because the queue mapping in the >>> driver gets complicated if it is greater than 4. We can probably >>> increase this latter. But sorry reiterating how is this different than >>> a macvtap on a real device that supports a max of 4 queues? >> >> Well, it maybe easy. I just point out possible issues we may meet >> currently. > > Right. > >>> >>>> So more works need to be done and unless those above 3 issues were >>>> addressed, this patch is really needed to make sure macvtap works. >>>> >>> >>> Agreed there is a lot more work here to improve things I'm just not >>> sure we need to disable this now. Also note its the l2 forwarding >>> should be disabled by default so a user would have to enable the >>> feature flag. >> >> Even if it was disabled by default. We should not surprise the user who >> want to enable it for macvtap. > > So the question is what to do in net while we improve net-next. Either > we fix the crash from the null txq and note that with l2 forwarding > some non default configuration is needed for optimal performance OR > for now disable it as your patch does. I would prefer to fix the crash > and note the configuration but I see your point about surprising users > so could go either way. > It's much safer to disable l2 forwarding offload for macvtap temporarily consider it has several issues.We can re-enable it when everything is ready in net-next. We we really need to hold the txq lock of lower device, only add more check of NULL pointer is not sufficient. So explicitly select a txq is still needed. And I don't see any conflicts between this and future enhancement. Also I don't see any drawback of using NETIF_F_LLTX for l2 forwarding. So we'd better keep it. > Neil any thoughts? > > To fix the null txq in the gso case adding a check for a non-null > txq before calling txq_trans_update() makes sense to me. We already > have the check in the non-gso case so making it symmetric fixes it. > >>> >>> Thanks, >>> John >>> >> >> Thanks >> > > -- > To unsubscribe from this list: send the line "unsubscribe netdev" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Tue, Jan 07, 2014 at 05:00:29PM +0800, Jason Wang wrote: > On 01/07/2014 03:26 PM, John Fastabend wrote: > > [...] > > > >>>> Unfortunately not. This commit has a side effect that it in fact > >>>> disables the multiqueue macvtap transmission. Since all macvtap queues > >>>> will contend on a single qdisc lock. > >>>> > >>> > >>> They will only contend on a single qdisc lock if the lower device has > >>> 1 queue. > >> > >> I think we are talking about 6acf54f1cf0a6747bac9fea26f34cfc5a9029523. > > > > Yes. > > > >> > >> The qdisc or txq lock were macvlan device itself since dev_queue_xmit() > >> was called for macvlan device itself. So even if lower device has > >> multiple txqs, if you just create a one queue macvlan device, you will > >> get lock contention on macvlan device. And even if you explicitly > >> specifying the txq numbers ( though I don't believe most management > >> software will do this) when creating the macvlan/macvtap device, you > >> must also configure the XPS for macvlan to make sure it has the > >> possibility of using multiple transmit queues. > >> > > > > OK I think I'm finally putting all the pieces together thanks. > > > > Do you know why macvtap is setting dev->tx_queue_len by default? If you > > zero this then the noqueue_qdisc is used and the q->enqueue check in > > dev_queue_xmit will fail. > > It was introduced in commit 8a35747a5d13b99e076b0222729e0caa48cb69b6 > ("macvtap: Limit packet queue length") to limit the length of socket > receive queue of macvtap. But I'm not sure whether the qdisc is a > byproduct of this commit, maybe we can switch to use another name > instead of just reuse dev->tx_queue_length. You mean tx_queue_len really, right? Problem is tx_queue_len can be accessed using netlink sysfs or ioctl, so if someone uses these to control or check the # of packets that can be queued by device, this will break. How about adding ndo_set_tx_queue_len then? At some point we wanted to decouple queue length from tx_queue_length for tun as well, so that would be benefitial there as well. > > > > Also if XPS is not configured then skb_tx_hash is used so multiple > > transmit queues will still be used. > > > > True. > >>> Perhaps defaulting the L2 forwarding devices to 1queue was a > >>> mistake. But the same issue arises when running macvtap over a > >>> non-multiqueue nic. Or even if you have a multiqueue device and create > >>> many more macvtap queues than the lower device has queues. > >>> > >>> Shouldn't the macvtap configuration take into account the lowest level > >>> devices queues? > >> > >> See commit 8ffab51b3dfc54876f145f15b351c41f3f703195 ("macvlan: lockless > >> tx path"). It allows the management to create a device without worrying > >> the underlying device. > > > > OK. > > > >>> How does using the L2 forwarding device change the > >>> contention issues? Without the L2 forwarding LLTX is enabled but the > >>> qdisc lock, etc is still acquired on the device below the macvlan. > >>> > >> > >> That's the point. We need make sure the txq selection and qdisc lock > >> were done for the lower device not for the macvlan device itself. Then > >> macvlan can automatically benefit from the multi-queue capable lower > >> devices. But L2 forwarding needs to contend on the txq lock on macvlan > >> device itself, which is unnecessary and can complex the management. > > > > If I make the l2 forwarding defaults a bit better then using the L2 > > forwarding case should not be any more complex. And because the queues > > are dedicated to the macvtap device any contention from qdisc lock, etc > > comes from the upper device only. > > At very least the txq of lower device should be held in order to be > synchronized with management path. Consider txq lock were often held by > netif_tx_disable() before trying to down the card. Current cold does not > hold txq lock, so it loses the synchronization which may cause issues. > And the code also does not check whether the txq has been stopped before > trying to start the transmission. > > > > Also if I get the bandwidth controls > > in we can set the max/min bandwidth per macvtap device this way. That > > is future work though. > > > > That will be a nice feature. > >>> The ixgbe driver as it is currently written can be configured for up to > >>> 4 queues by setting numtxqueues when the device is created. I assume > >>> when creating macvtap queues the user needs to account for the number > >>> of queues supported by the lower device. > >>> > >> > >> We'd better not complicate the task of management, lockless tx path work > >> very well so we can just keep it. Btw, there's no way for the user to > >> know the maximum number of queues that L2 forwarding supports. > > > > Good point I'll add an attribute to query it. > > > >>>> For L2 forwarding offload itself, more issues need to be addressed for > >>>> multiqueue macvtap: > >>>> > >>>> - ndo_dfwd_add_station() can only create queues per device at > >>>> ndo_open, > >>>> but multiqueue macvtap allows user to create and destroy queues at > >>>> their > >>>> will and at any time. > >>> > >>> same argument as above, isn't this the same when running macvtap > >>> without > >>> the l2 offloads over a real device? I expect you hit the same > >>> contention > >>> points when running over a real device. > >> > >> Not true and not only for contention. > >> > >> Macvtap allows user to create or destroy a queue by simply open or close > >> to character device /dev/tapX. But currently, we do nothing when a new > >> queue was created or destroyed for L2 forwarding offload. > >> > >> For contention, lockless tx path make the contention only happens for > >> the txq or qdisc for the lower device, but L2 forwarding offload make > >> contention also happen for the macvlan device itself. > > > > Right, but there will be less contention there because those queues > > are a dedicated resource for the upper device. > > Yes and this is also true if we only do synchronization on the lower > device since only dedicated queues could be selected. > > > > At this point I think I need to put together a real testbed and > > benchmark some of this with netperf and perf running to get real > > numbers. When I originally did the l2 forwarding I did not do any > > testing with multiple macvtap queues and only very limited work with > > macvtap. > > > > As I said above, holding the txq lock of lower device seems a must and > we should not get regression if NETIF_F_LLTX is kept. But I agree we > need some test. > >> > >>> > >>> > >>>> - it looks that ixgbe has a upper limit of 4 queues per station, but > >>>> macvtap currently allows up to 16 queues per device. > >>>> > >>> > >>> The 4 limit was to simplify the code because the queue mapping in the > >>> driver gets complicated if it is greater than 4. We can probably > >>> increase this latter. But sorry reiterating how is this different than > >>> a macvtap on a real device that supports a max of 4 queues? > >> > >> Well, it maybe easy. I just point out possible issues we may meet > >> currently. > > > > Right. > > > >>> > >>>> So more works need to be done and unless those above 3 issues were > >>>> addressed, this patch is really needed to make sure macvtap works. > >>>> > >>> > >>> Agreed there is a lot more work here to improve things I'm just not > >>> sure we need to disable this now. Also note its the l2 forwarding > >>> should be disabled by default so a user would have to enable the > >>> feature flag. > >> > >> Even if it was disabled by default. We should not surprise the user who > >> want to enable it for macvtap. > > > > So the question is what to do in net while we improve net-next. Either > > we fix the crash from the null txq and note that with l2 forwarding > > some non default configuration is needed for optimal performance OR > > for now disable it as your patch does. I would prefer to fix the crash > > and note the configuration but I see your point about surprising users > > so could go either way. > > > > It's much safer to disable l2 forwarding offload for macvtap temporarily > consider it has several issues.We can re-enable it when everything is > ready in net-next. We we really need to hold the txq lock of lower > device, only add more check of NULL pointer is not sufficient. So > explicitly select a txq is still needed. And I don't see any conflicts > between this and future enhancement. > > Also I don't see any drawback of using NETIF_F_LLTX for l2 forwarding. > So we'd better keep it. > > Neil any thoughts? > > > > To fix the null txq in the gso case adding a check for a non-null > > txq before calling txq_trans_update() makes sense to me. We already > > have the check in the non-gso case so making it symmetric fixes it. > > > >>> > >>> Thanks, > >>> John > >>> > >> > >> Thanks > >> > > > > -- > > To unsubscribe from this list: send the line "unsubscribe netdev" in > > the body of a message to majordomo@vger.kernel.org > > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[...] >>> OK I think I'm finally putting all the pieces together thanks. >>> >>> Do you know why macvtap is setting dev->tx_queue_len by default? If you >>> zero this then the noqueue_qdisc is used and the q->enqueue check in >>> dev_queue_xmit will fail. >> >> It was introduced in commit 8a35747a5d13b99e076b0222729e0caa48cb69b6 >> ("macvtap: Limit packet queue length") to limit the length of socket >> receive queue of macvtap. But I'm not sure whether the qdisc is a >> byproduct of this commit, maybe we can switch to use another name >> instead of just reuse dev->tx_queue_length. > > You mean tx_queue_len really, right? > > Problem is tx_queue_len can be accessed using netlink sysfs or ioctl, > so if someone uses these to control or check the # of packets that > can be queued by device, this will break. > > How about adding ndo_set_tx_queue_len then? > > At some point we wanted to decouple queue length from tx_queue_length > for tun as well, so that would be benefitial there as well. On the receive side we need to limit the receive queue and the dev->tx_queue_len value was used to do this. However on the tx side when dev->tx_queue_len is set the default qdisc pfifo_fast or mq is used depending on if there is multiqueue or not. Unless the user specifies some numtxqueues when creating the macvtap device then it will be a single queue device and use the pfifo_fast qdisc. This is the default behaviour users could zero txqueuelen when they create the device because it is a stacked device with NETIF_F_LLTX using the lower devices qdisc makes sense but this would appear (from code inspection) to break macvtap_forward()? if (skb_queue_len(&q->sk.sk_receive_queue) >= dev->tx_queue_len) goto drop; I'm not sure any of this is a problem other than its a bit confusing to overload tx_queue_len for the rx_queue_len but the precedent has been there for sometime. It is a change in behaviour though in net-next. Previously dev_queue_xmit() was not used so the qdisc layer was never hit on the macvtap device. Now with dev_queue_xmit() if the user attaches multiple macvlan queues to a single qdisc queue this should still work but wont be optimal. Ideally the user should create as many qdisc queues at creation time via numtxqueues as macvtap queues will be used during runtime so that there is a 1:1 mapping or use some heuristic to avoid cases where there is a many to 1 mapping. From my perspective it would be OK to push this configuration/policy to the management layer. After all it is the entity that knows how to distribute system resources amongst the objects running over the macvtap devices. The relevance for me is I defaulted the l2 offloaded macvlans to single queue devices and wanted to note in net-next this is the same policy used in the non-offloaded case. Bit long-winded there. Thanks, John -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/drivers/net/macvlan.c b/drivers/net/macvlan.c index 60406b0..5360f73 100644 --- a/drivers/net/macvlan.c +++ b/drivers/net/macvlan.c @@ -338,6 +338,8 @@ static const struct header_ops macvlan_hard_header_ops = { .cache_update = eth_header_cache_update, }; +static struct rtnl_link_ops macvlan_link_ops; + static int macvlan_open(struct net_device *dev) { struct macvlan_dev *vlan = netdev_priv(dev); @@ -353,7 +355,8 @@ static int macvlan_open(struct net_device *dev) goto hash_add; } - if (lowerdev->features & NETIF_F_HW_L2FW_DOFFLOAD) { + if (lowerdev->features & NETIF_F_HW_L2FW_DOFFLOAD && + dev->rtnl_link_ops == &macvlan_link_ops) { vlan->fwd_priv = lowerdev->netdev_ops->ndo_dfwd_add_station(lowerdev, dev);
L2 fowarding offload will bypass the rx handler of real device. This will make the packet could not be forwarded to macvtap device. Another problem is the dev_hard_start_xmit() called for macvtap does not have any synchronization. Fix this by forbidding L2 forwarding for macvtap. Cc: John Fastabend <john.r.fastabend@intel.com> Cc: Neil Horman <nhorman@tuxdriver.com> Signed-off-by: Jason Wang <jasowang@redhat.com> --- drivers/net/macvlan.c | 5 ++++- 1 files changed, 4 insertions(+), 1 deletions(-)