| Message ID | X8f/WKR6/j9k+vMz@black-debian |
|---|---|
| State | Not Applicable |
| Headers | show |
| Series | [net-next] bonding: correct rr balancing during link failure | expand |
On Wed, 02 Dec 2020 20:55:57 +0000 Lars Everbrand wrote: > This patch updates the sending algorithm for roundrobin to avoid > over-subscribing interface(s) when one or more interfaces in the bond is > not able to send packets. This happened when order was not random and > more than 2 interfaces were used. > > Previously the algorithm would find the next available interface > when an interface failed to send by, this means that most often it is > current_interface + 1. The problem is that when the next packet is to be > sent and the "normal" algorithm then continues with interface++ which > then hits that same interface again. > > This patch updates the resending algorithm to update the global counter > of the next interface to use. > > Example (prior to patch): > > Consider 6 x 100 Mbit/s interfaces in a rr bond. The normal order of links > being used to send would look like: > 1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6 ... > > If, for instance, interface 2 where unable to send the order would have been: > 1 3 3 4 5 6 1 3 3 4 5 6 1 3 3 4 5 6 ... > > The resulting speed (for TCP) would then become: > 50 + 0 + 100 + 50 + 50 + 50 = 300 Mbit/s > instead of the expected 500 Mbit/s. > > If interface 3 also would fail the resulting speed would be half of the > expected 400 Mbit/s (33 + 0 + 0 + 100 + 33 + 33). > > Signed-off-by: Lars Everbrand <lars.everbrand@protonmail.com> Thanks for the patch! Looking at the code in question it feels a little like we're breaking abstractions if we bump the counter directly in get_slave_by_id. For one thing when the function is called for IGMP packets the counter should not be incremented at all. But also if packets_per_slave is not 1 we'd still be hitting the same leg multiple times (packets_per_slave / 2). So it seems like we should round the counter up somehow? For IGMP maybe we don't have to call bond_get_slave_by_id() at all, IMHO, just find first leg that can TX. Then we can restructure bond_get_slave_by_id() appropriately for the non-IGMP case. > diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c > index e0880a3840d7..e02d9c6d40ee 100644 > --- a/drivers/net/bonding/bond_main.c > +++ b/drivers/net/bonding/bond_main.c > @@ -4107,6 +4107,7 @@ static struct slave *bond_get_slave_by_id(struct bonding *bond, > if (--i < 0) { > if (bond_slave_can_tx(slave)) > return slave; > + bond->rr_tx_counter++; > } > } > > @@ -4117,6 +4118,7 @@ static struct slave *bond_get_slave_by_id(struct bonding *bond, > break; > if (bond_slave_can_tx(slave)) > return slave; > + bond->rr_tx_counter++; > } > /* no slave that can tx has been found */ > return NULL;
Jakub Kicinski <kuba@kernel.org> wrote: >On Wed, 02 Dec 2020 20:55:57 +0000 Lars Everbrand wrote: >> This patch updates the sending algorithm for roundrobin to avoid >> over-subscribing interface(s) when one or more interfaces in the bond is >> not able to send packets. This happened when order was not random and >> more than 2 interfaces were used. >> >> Previously the algorithm would find the next available interface >> when an interface failed to send by, this means that most often it is >> current_interface + 1. The problem is that when the next packet is to be >> sent and the "normal" algorithm then continues with interface++ which >> then hits that same interface again. >> >> This patch updates the resending algorithm to update the global counter >> of the next interface to use. >> >> Example (prior to patch): >> >> Consider 6 x 100 Mbit/s interfaces in a rr bond. The normal order of links >> being used to send would look like: >> 1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6 ... >> >> If, for instance, interface 2 where unable to send the order would have been: >> 1 3 3 4 5 6 1 3 3 4 5 6 1 3 3 4 5 6 ... >> >> The resulting speed (for TCP) would then become: >> 50 + 0 + 100 + 50 + 50 + 50 = 300 Mbit/s >> instead of the expected 500 Mbit/s. >> >> If interface 3 also would fail the resulting speed would be half of the >> expected 400 Mbit/s (33 + 0 + 0 + 100 + 33 + 33). Are these bandwidth numbers from observation of the actual behavior? I'm not sure the real system would behave this way; my suspicion is that it would increase the likelihood of drops on the overused slave, not that the overall capacity would be limited. >> Signed-off-by: Lars Everbrand <lars.everbrand@protonmail.com> > >Thanks for the patch! > >Looking at the code in question it feels a little like we're breaking >abstractions if we bump the counter directly in get_slave_by_id. Agreed; I think a better way to fix this is to enable the slave array for balance-rr mode, and then use the array to find the right slave. This way, we then avoid the problematic "skip unable to tx" logic for free. >For one thing when the function is called for IGMP packets the counter >should not be incremented at all. But also if packets_per_slave is not >1 we'd still be hitting the same leg multiple times (packets_per_slave >/ 2). So it seems like we should round the counter up somehow? > >For IGMP maybe we don't have to call bond_get_slave_by_id() at all, >IMHO, just find first leg that can TX. Then we can restructure >bond_get_slave_by_id() appropriately for the non-IGMP case. For IGMP, the theory is to confine that traffic to a single device. Normally, this will be curr_active_slave, which is updated even in balance-rr mode as interfaces are added to or removed from the bond. The call to bond_get_slave_by_id should be a fallback in case curr_active_slave is empty, and should be the exception, and may not be possible at all. But either way, the IGMP path shouldn't mess with rr_tx_counter, it should be out of band of the normal TX packet counting, so to speak. -J >> diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c >> index e0880a3840d7..e02d9c6d40ee 100644 >> --- a/drivers/net/bonding/bond_main.c >> +++ b/drivers/net/bonding/bond_main.c >> @@ -4107,6 +4107,7 @@ static struct slave *bond_get_slave_by_id(struct bonding *bond, >> if (--i < 0) { >> if (bond_slave_can_tx(slave)) >> return slave; >> + bond->rr_tx_counter++; >> } >> } >> >> @@ -4117,6 +4118,7 @@ static struct slave *bond_get_slave_by_id(struct bonding *bond, >> break; >> if (bond_slave_can_tx(slave)) >> return slave; >> + bond->rr_tx_counter++; >> } >> /* no slave that can tx has been found */ >> return NULL; > --- -Jay Vosburgh, jay.vosburgh@canonical.com
diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c index e0880a3840d7..e02d9c6d40ee 100644 --- a/drivers/net/bonding/bond_main.c +++ b/drivers/net/bonding/bond_main.c @@ -4107,6 +4107,7 @@ static struct slave *bond_get_slave_by_id(struct bonding *bond, if (--i < 0) { if (bond_slave_can_tx(slave)) return slave; + bond->rr_tx_counter++; } } @@ -4117,6 +4118,7 @@ static struct slave *bond_get_slave_by_id(struct bonding *bond, break; if (bond_slave_can_tx(slave)) return slave; + bond->rr_tx_counter++; } /* no slave that can tx has been found */ return NULL;
This patch updates the sending algorithm for roundrobin to avoid over-subscribing interface(s) when one or more interfaces in the bond is not able to send packets. This happened when order was not random and more than 2 interfaces were used. Previously the algorithm would find the next available interface when an interface failed to send by, this means that most often it is current_interface + 1. The problem is that when the next packet is to be sent and the "normal" algorithm then continues with interface++ which then hits that same interface again. This patch updates the resending algorithm to update the global counter of the next interface to use. Example (prior to patch): Consider 6 x 100 Mbit/s interfaces in a rr bond. The normal order of links being used to send would look like: 1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6 ... If, for instance, interface 2 where unable to send the order would have been: 1 3 3 4 5 6 1 3 3 4 5 6 1 3 3 4 5 6 ... The resulting speed (for TCP) would then become: 50 + 0 + 100 + 50 + 50 + 50 = 300 Mbit/s instead of the expected 500 Mbit/s. If interface 3 also would fail the resulting speed would be half of the expected 400 Mbit/s (33 + 0 + 0 + 100 + 33 + 33). Signed-off-by: Lars Everbrand <lars.everbrand@protonmail.com> --- drivers/net/bonding/bond_main.c | 2 ++ 1 file changed, 2 insertions(+)