QEMU -netdev vhost=on + -device virtio-net-pci bug

Submitted by Alexey Kardashevskiy on March 5, 2013, 10:57 p.m.

Details

Message ID 51367864.6080502@ozlabs.ru
State New
Headers show

Commit Message

Alexey Kardashevskiy March 5, 2013, 10:57 p.m.
On 06/03/13 01:23, Michael S. Tsirkin wrote:
> On Wed, Mar 06, 2013 at 12:21:47AM +1100, Alexey Kardashevskiy wrote:
>> On 05/03/13 23:56, Michael S. Tsirkin wrote:
>>>> The patch f56a12475ff1b8aa61210d08522c3c8aaf0e2648 "vhost: backend
>>>> masking support" breaks virtio-net + vhost=on on PPC64 platform.
>>>>
>>>> The problem command line is:
>>>> 1) -netdev tap,id=tapnet,ifname=tap0,script=qemu-ifup.sh,vhost=on \
>>>> -device virtio-net-pci,netdev=tapnet,addr=0.0 \
>>>
>>> I think the issue is irqfd in not supported on kvm ppc.
>>
>> How can I make sure this is the case? Some work has been done there
>> recently but midnight is quite late to figure this out :)
>
> Look in virtio_pci_set_guest_notifiers, what is the
> value of with_irqfd?
>    bool with_irqfd = msix_enabled(&proxy->pci_dev) &&
>          kvm_msi_via_irqfd_enabled();
>
> Also check what each of the values in the expression above is.

Yes, ppc does not have irqfd as kvm_msi_via_irqfd_enabled() returned "false".

>>> Could you please check this:
>>>
>>> +        /* If guest supports masking, set up irqfd now.
>>> +         * Otherwise, delay until unmasked in the frontend.
>>> +         */
>>> +        if (proxy->vdev->guest_notifier_mask) {
>>> +            ret = kvm_virtio_pci_irqfd_use(proxy, queue_no, vector);
>>> +            if (ret < 0) {
>>> +                kvm_virtio_pci_vq_vector_release(proxy, vector);
>>> +                goto undo;
>>> +            }
>>> +        }
>>>
>>>
>>> Could you please add a printf before "undo" and check whether the
>>> error path above is triggered?
>>
>>
>> Checked, it is not triggered.
>>
>>
>> --
>> Alexey
>
> I think I get it.
> Does the following help (probably not the right thing to do, but just
> for testing):


It did not compile (no "queue_no") :) I changed it a bit and now vhost=on 
works fine:

      /* Must set vector notifier after guest notifier has been assigned */




> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
>
> ---
>
> diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
> index ba56ab2..c2a0c5a 100644
> --- a/hw/virtio-pci.c
> +++ b/hw/virtio-pci.c
> @@ -800,6 +800,10 @@ static int virtio_pci_set_guest_notifiers(DeviceState *d, int nvqs, bool assign)
>           }
>       }
>
> +    if (!with_irqfd && proxy->vdev->guest_notifier_mask) {
> +        proxy->vdev->guest_notifier_mask(proxy->vdev, queue_no, !assign);
> +    }
> +
>       /* Must set vector notifier after guest notifier has been assigned */
>       if (with_irqfd && assign) {
>           proxy->vector_irqfd =
>

Comments

Michael S. Tsirkin March 6, 2013, 10:31 a.m.
On Wed, Mar 06, 2013 at 09:57:40AM +1100, Alexey Kardashevskiy wrote:
> On 06/03/13 01:23, Michael S. Tsirkin wrote:
> >On Wed, Mar 06, 2013 at 12:21:47AM +1100, Alexey Kardashevskiy wrote:
> >>On 05/03/13 23:56, Michael S. Tsirkin wrote:
> >>>>The patch f56a12475ff1b8aa61210d08522c3c8aaf0e2648 "vhost: backend
> >>>>masking support" breaks virtio-net + vhost=on on PPC64 platform.
> >>>>
> >>>>The problem command line is:
> >>>>1) -netdev tap,id=tapnet,ifname=tap0,script=qemu-ifup.sh,vhost=on \
> >>>>-device virtio-net-pci,netdev=tapnet,addr=0.0 \
> >>>
> >>>I think the issue is irqfd in not supported on kvm ppc.
> >>
> >>How can I make sure this is the case? Some work has been done there
> >>recently but midnight is quite late to figure this out :)
> >
> >Look in virtio_pci_set_guest_notifiers, what is the
> >value of with_irqfd?
> >   bool with_irqfd = msix_enabled(&proxy->pci_dev) &&
> >         kvm_msi_via_irqfd_enabled();
> >
> >Also check what each of the values in the expression above is.
> 
> Yes, ppc does not have irqfd as kvm_msi_via_irqfd_enabled() returned "false".
> 
> >>>Could you please check this:
> >>>
> >>>+        /* If guest supports masking, set up irqfd now.
> >>>+         * Otherwise, delay until unmasked in the frontend.
> >>>+         */
> >>>+        if (proxy->vdev->guest_notifier_mask) {
> >>>+            ret = kvm_virtio_pci_irqfd_use(proxy, queue_no, vector);
> >>>+            if (ret < 0) {
> >>>+                kvm_virtio_pci_vq_vector_release(proxy, vector);
> >>>+                goto undo;
> >>>+            }
> >>>+        }
> >>>
> >>>
> >>>Could you please add a printf before "undo" and check whether the
> >>>error path above is triggered?
> >>
> >>
> >>Checked, it is not triggered.
> >>
> >>
> >>--
> >>Alexey
> >
> >I think I get it.
> >Does the following help (probably not the right thing to do, but just
> >for testing):
> 
> 
> It did not compile (no "queue_no") :) I changed it a bit and now
> vhost=on works fine:
> 
> diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
> index a869f53..df1e443 100644
> --- a/hw/virtio-pci.c
> +++ b/hw/virtio-pci.c
> @@ -798,6 +798,10 @@ static int
> virtio_pci_set_guest_notifiers(DeviceState *d, int nvqs, bool
> assign)
>          if (r < 0) {
>              goto assign_error;
>          }
> +
> +        if (!with_irqfd && proxy->vdev->guest_notifier_mask) {
> +            proxy->vdev->guest_notifier_mask(proxy->vdev, n, !assign);
> +        }
>      }
> 
>      /* Must set vector notifier after guest notifier has been assigned */
> 
> 

I see, OK, the issue is that vhost now starts in a masked state
and no one unmasks it. While the patch will work I think,
it does not benefit from backend masking, the right thing
to do is to add mask notifiers, like what the irqfd path does.

Will look into this, thanks.
Alexey Kardashevskiy March 8, 2013, 4:48 a.m.
Michael,

Thanks for the fix.

There was another question which was lost in the thread.

I am testing virtio-net in two ways:

Old -net interface:
-net tap,ifname=tap0,script=qemu-ifup.sh \
-net nic,model=virtio,addr=0:0:0

(qemu) info network
hub 0
  \ virtio-net-pci.0: 
index=0,type=nic,model=virtio-net-pci,macaddr=52:54:00:12:34:56
  \ tap.0: 
index=0,type=tap,ifname=tap0,script=qemu-ifup.sh,downscript=/etc/qemu-ifdown

New -netdev interface:
-netdev tap,id=tapnet,ifname=tap0,script=qemu-ifup.sh \
-device virtio-net-pci,netdev=tapnet,addr=0.0

(qemu) info network
virtio-net-pci.0: 
index=0,type=nic,model=virtio-net-pci,macaddr=52:54:00:12:34:56
  \ tapnet: 
index=0,type=tap,ifname=tap0,script=qemu-ifup.sh,downscript=/etc/qemu-ifdown


I get very different virtio0 device features and speed (70MB/s vs. 
700MB/s). I guess somehow the "hub 0" is responsible but there is no way to 
avoid it.

Is there any way to speed up the virtio-net using the old -net interface?



On 06/03/13 21:31, Michael S. Tsirkin wrote:
> On Wed, Mar 06, 2013 at 09:57:40AM +1100, Alexey Kardashevskiy wrote:
>> On 06/03/13 01:23, Michael S. Tsirkin wrote:
>>> On Wed, Mar 06, 2013 at 12:21:47AM +1100, Alexey Kardashevskiy wrote:
>>>> On 05/03/13 23:56, Michael S. Tsirkin wrote:
>>>>>> The patch f56a12475ff1b8aa61210d08522c3c8aaf0e2648 "vhost: backend
>>>>>> masking support" breaks virtio-net + vhost=on on PPC64 platform.
>>>>>>
>>>>>> The problem command line is:
>>>>>> 1) -netdev tap,id=tapnet,ifname=tap0,script=qemu-ifup.sh,vhost=on \
>>>>>> -device virtio-net-pci,netdev=tapnet,addr=0.0 \
>>>>>
>>>>> I think the issue is irqfd in not supported on kvm ppc.
>>>>
>>>> How can I make sure this is the case? Some work has been done there
>>>> recently but midnight is quite late to figure this out :)
>>>
>>> Look in virtio_pci_set_guest_notifiers, what is the
>>> value of with_irqfd?
>>>    bool with_irqfd = msix_enabled(&proxy->pci_dev) &&
>>>          kvm_msi_via_irqfd_enabled();
>>>
>>> Also check what each of the values in the expression above is.
>>
>> Yes, ppc does not have irqfd as kvm_msi_via_irqfd_enabled() returned "false".
>>
>>>>> Could you please check this:
>>>>>
>>>>> +        /* If guest supports masking, set up irqfd now.
>>>>> +         * Otherwise, delay until unmasked in the frontend.
>>>>> +         */
>>>>> +        if (proxy->vdev->guest_notifier_mask) {
>>>>> +            ret = kvm_virtio_pci_irqfd_use(proxy, queue_no, vector);
>>>>> +            if (ret < 0) {
>>>>> +                kvm_virtio_pci_vq_vector_release(proxy, vector);
>>>>> +                goto undo;
>>>>> +            }
>>>>> +        }
>>>>>
>>>>>
>>>>> Could you please add a printf before "undo" and check whether the
>>>>> error path above is triggered?
>>>>
>>>>
>>>> Checked, it is not triggered.
>>>>
>>>>
>>>> --
>>>> Alexey
>>>
>>> I think I get it.
>>> Does the following help (probably not the right thing to do, but just
>>> for testing):
>>
>>
>> It did not compile (no "queue_no") :) I changed it a bit and now
>> vhost=on works fine:
>>
>> diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
>> index a869f53..df1e443 100644
>> --- a/hw/virtio-pci.c
>> +++ b/hw/virtio-pci.c
>> @@ -798,6 +798,10 @@ static int
>> virtio_pci_set_guest_notifiers(DeviceState *d, int nvqs, bool
>> assign)
>>           if (r < 0) {
>>               goto assign_error;
>>           }
>> +
>> +        if (!with_irqfd && proxy->vdev->guest_notifier_mask) {
>> +            proxy->vdev->guest_notifier_mask(proxy->vdev, n, !assign);
>> +        }
>>       }
>>
>>       /* Must set vector notifier after guest notifier has been assigned */
>>
>>
>
> I see, OK, the issue is that vhost now starts in a masked state
> and no one unmasks it. While the patch will work I think,
> it does not benefit from backend masking, the right thing
> to do is to add mask notifiers, like what the irqfd path does.
>
> Will look into this, thanks.
>
Michael S. Tsirkin March 10, 2013, 9:24 a.m.
On Fri, Mar 08, 2013 at 03:48:04PM +1100, Alexey Kardashevskiy wrote:
> Michael,
> 
> Thanks for the fix.
> 
> There was another question which was lost in the thread.
> 
> I am testing virtio-net in two ways:
> 
> Old -net interface:
> -net tap,ifname=tap0,script=qemu-ifup.sh \
> -net nic,model=virtio,addr=0:0:0
> 
> (qemu) info network
> hub 0
>  \ virtio-net-pci.0:
> index=0,type=nic,model=virtio-net-pci,macaddr=52:54:00:12:34:56
>  \ tap.0: index=0,type=tap,ifname=tap0,script=qemu-ifup.sh,downscript=/etc/qemu-ifdown
> 
> New -netdev interface:
> -netdev tap,id=tapnet,ifname=tap0,script=qemu-ifup.sh \
> -device virtio-net-pci,netdev=tapnet,addr=0.0
> 
> (qemu) info network
> virtio-net-pci.0:
> index=0,type=nic,model=virtio-net-pci,macaddr=52:54:00:12:34:56
>  \ tapnet: index=0,type=tap,ifname=tap0,script=qemu-ifup.sh,downscript=/etc/qemu-ifdown
> 
> 
> I get very different virtio0 device features and speed (70MB/s vs.
> 700MB/s). I guess somehow the "hub 0" is responsible but there is no
> way to avoid it.
> 
> Is there any way to speed up the virtio-net using the old -net interface?

Not at the moment. Why do you want to use it?

> 
> On 06/03/13 21:31, Michael S. Tsirkin wrote:
> >On Wed, Mar 06, 2013 at 09:57:40AM +1100, Alexey Kardashevskiy wrote:
> >>On 06/03/13 01:23, Michael S. Tsirkin wrote:
> >>>On Wed, Mar 06, 2013 at 12:21:47AM +1100, Alexey Kardashevskiy wrote:
> >>>>On 05/03/13 23:56, Michael S. Tsirkin wrote:
> >>>>>>The patch f56a12475ff1b8aa61210d08522c3c8aaf0e2648 "vhost: backend
> >>>>>>masking support" breaks virtio-net + vhost=on on PPC64 platform.
> >>>>>>
> >>>>>>The problem command line is:
> >>>>>>1) -netdev tap,id=tapnet,ifname=tap0,script=qemu-ifup.sh,vhost=on \
> >>>>>>-device virtio-net-pci,netdev=tapnet,addr=0.0 \
> >>>>>
> >>>>>I think the issue is irqfd in not supported on kvm ppc.
> >>>>
> >>>>How can I make sure this is the case? Some work has been done there
> >>>>recently but midnight is quite late to figure this out :)
> >>>
> >>>Look in virtio_pci_set_guest_notifiers, what is the
> >>>value of with_irqfd?
> >>>   bool with_irqfd = msix_enabled(&proxy->pci_dev) &&
> >>>         kvm_msi_via_irqfd_enabled();
> >>>
> >>>Also check what each of the values in the expression above is.
> >>
> >>Yes, ppc does not have irqfd as kvm_msi_via_irqfd_enabled() returned "false".
> >>
> >>>>>Could you please check this:
> >>>>>
> >>>>>+        /* If guest supports masking, set up irqfd now.
> >>>>>+         * Otherwise, delay until unmasked in the frontend.
> >>>>>+         */
> >>>>>+        if (proxy->vdev->guest_notifier_mask) {
> >>>>>+            ret = kvm_virtio_pci_irqfd_use(proxy, queue_no, vector);
> >>>>>+            if (ret < 0) {
> >>>>>+                kvm_virtio_pci_vq_vector_release(proxy, vector);
> >>>>>+                goto undo;
> >>>>>+            }
> >>>>>+        }
> >>>>>
> >>>>>
> >>>>>Could you please add a printf before "undo" and check whether the
> >>>>>error path above is triggered?
> >>>>
> >>>>
> >>>>Checked, it is not triggered.
> >>>>
> >>>>
> >>>>--
> >>>>Alexey
> >>>
> >>>I think I get it.
> >>>Does the following help (probably not the right thing to do, but just
> >>>for testing):
> >>
> >>
> >>It did not compile (no "queue_no") :) I changed it a bit and now
> >>vhost=on works fine:
> >>
> >>diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
> >>index a869f53..df1e443 100644
> >>--- a/hw/virtio-pci.c
> >>+++ b/hw/virtio-pci.c
> >>@@ -798,6 +798,10 @@ static int
> >>virtio_pci_set_guest_notifiers(DeviceState *d, int nvqs, bool
> >>assign)
> >>          if (r < 0) {
> >>              goto assign_error;
> >>          }
> >>+
> >>+        if (!with_irqfd && proxy->vdev->guest_notifier_mask) {
> >>+            proxy->vdev->guest_notifier_mask(proxy->vdev, n, !assign);
> >>+        }
> >>      }
> >>
> >>      /* Must set vector notifier after guest notifier has been assigned */
> >>
> >>
> >
> >I see, OK, the issue is that vhost now starts in a masked state
> >and no one unmasks it. While the patch will work I think,
> >it does not benefit from backend masking, the right thing
> >to do is to add mask notifiers, like what the irqfd path does.
> >
> >Will look into this, thanks.
> >
> 
> 
> -- 
> Alexey
Alexey Kardashevskiy March 10, 2013, 11:25 a.m.
On 10/03/13 20:24, Michael S. Tsirkin wrote:
> On Fri, Mar 08, 2013 at 03:48:04PM +1100, Alexey Kardashevskiy wrote:
>> Michael,
>>
>> Thanks for the fix.
>>
>> There was another question which was lost in the thread.
>>
>> I am testing virtio-net in two ways:
>>
>> Old -net interface:
>> -net tap,ifname=tap0,script=qemu-ifup.sh \
>> -net nic,model=virtio,addr=0:0:0
>>
>> (qemu) info network
>> hub 0
>>   \ virtio-net-pci.0:
>> index=0,type=nic,model=virtio-net-pci,macaddr=52:54:00:12:34:56
>>   \ tap.0: index=0,type=tap,ifname=tap0,script=qemu-ifup.sh,downscript=/etc/qemu-ifdown
>>
>> New -netdev interface:
>> -netdev tap,id=tapnet,ifname=tap0,script=qemu-ifup.sh \
>> -device virtio-net-pci,netdev=tapnet,addr=0.0
>>
>> (qemu) info network
>> virtio-net-pci.0:
>> index=0,type=nic,model=virtio-net-pci,macaddr=52:54:00:12:34:56
>>   \ tapnet: index=0,type=tap,ifname=tap0,script=qemu-ifup.sh,downscript=/etc/qemu-ifdown
>>
>>
>> I get very different virtio0 device features and speed (70MB/s vs.
>> 700MB/s). I guess somehow the "hub 0" is responsible but there is no
>> way to avoid it.
>>
>> Is there any way to speed up the virtio-net using the old -net interface?
>
> Not at the moment. Why do you want to use it?


It is not like I really want it, I was just trying to understand (now it is
more or less clear) why exactly "not" as the documentation is saying about 
-net and -netdev as synonyms while they are not.

Patch hide | download patch | download mbox

diff --git a/hw/virtio-pci.c b/hw/virtio-pci.c
index a869f53..df1e443 100644
--- a/hw/virtio-pci.c
+++ b/hw/virtio-pci.c
@@ -798,6 +798,10 @@  static int virtio_pci_set_guest_notifiers(DeviceState 
*d, int nvqs, bool assign)
          if (r < 0) {
              goto assign_error;
          }
+
+        if (!with_irqfd && proxy->vdev->guest_notifier_mask) {
+            proxy->vdev->guest_notifier_mask(proxy->vdev, n, !assign);
+        }
      }