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Message-ID: <CAL8zT=gm_1R2NuC0Tfii+Vpy1eu2tUXgVBa8g+i=9Ojs8T_p+A@mail.gmail.com> Date: Thu, 19 Jan 2012 16:52:09 +0100 From: Jean-Michel Hautbois <jhautbois@...il.com> To: Eric Dumazet <eric.dumazet@...il.com> Cc: netdev <netdev@...r.kernel.org>, Jean-Michel Hautbois <jhautbois@...il.com> Subject: Re: MSI-X and interrupt affinity with Emulex be2net 2012/1/19 Eric Dumazet <eric.dumazet@...il.com>: > Le jeudi 19 janvier 2012 à 15:33 +0100, Jean-Michel Hautbois a écrit : >> Hi all, >> >> I am using a be2net ethernet interface, and am on the master git >> repository, so the latest kernel available. >> I have MSI-X enabled of course, and as far as I can tell, all >> interrupts are bound to CPU0. >> I have several process and threads which use quite all the ethernet >> interfaces I have, and I reach 7180 IRQs/sec on CPU0. >> >> I have several questions regarding this : >> - I thought MSI-X would help in balancing IRQs on different CPUs > > with some help from admin (or irqbalance ?), yes... Irqbalance is a nice tool, and I thought MSI-X would be automatic on this particular stuff... >> - Is this a good idea anyway to specify which IRQ is bound to which >> CPU manually, if I set the process using the IRQ to the same CPU ? > > There is no general answer to this question unfortunately. > > It all depends on the workload, the number of flows, balance between > transmits and receives ... > > Also be2net has one single interrupt for the tx-completion side. > > For example, IP defragmentation uses a rwlock, so splitting your trafic > to several cpus might increase false sharing and contention. > > About the "all interrupts on CPU0", this is what happens with default > smp_affinity settings. > > Here I have a be2net and can change IRQ affinities with no problem > > # grep eth3 /proc/interrupts > 76: 1418189 0 0 0 0 0 > 0 0 0 0 0 0 0 > 0 0 0 PCI-MSI-edge eth3-tx > 77: 24831 0 0 0 0 0 > 0 0 0 0 0 0 0 > 0 0 0 PCI-MSI-edge eth3-rxq0 > 78: 5147 0 0 0 0 0 > 0 0 0 0 0 0 0 > 0 0 0 PCI-MSI-edge eth3-rxq1 > 79: 7 0 0 0 0 0 > 0 0 0 0 0 0 0 > 0 0 0 PCI-MSI-edge eth3-rxq2 > 80: 2 0 0 0 0 0 > 0 0 0 0 0 0 0 > 0 0 0 PCI-MSI-edge eth3-rxq3 > 81: 118 0 0 0 0 0 > 0 0 0 0 0 0 0 > 0 0 0 PCI-MSI-edge eth3-rxq4 > # cat /proc/irq/77/smp_affinity > ffff > # echo 2 >/proc/irq/77/smp_affinity > # echo 4 >/proc/irq/78/smp_affinity > # echo 8 >/proc/irq/79/smp_affinity > # echo 10 >/proc/irq/80/smp_affinity > # echo 20 >/proc/irq/81/smp_affinity > # grep eth3 /proc/interrupts > 76: 1426698 0 0 0 0 0 > 0 0 0 0 0 0 0 > 0 0 0 PCI-MSI-edge eth3-tx > 77: 24832 7 0 0 0 0 > 0 0 0 0 0 0 0 > 0 0 0 PCI-MSI-edge eth3-rxq0 > 78: 5318 0 3489 0 0 0 > 0 0 0 0 0 0 0 > 0 0 0 PCI-MSI-edge eth3-rxq1 > 79: 7 0 0 0 0 0 > 0 0 0 0 0 0 0 > 0 0 0 PCI-MSI-edge eth3-rxq2 > 80: 3 0 0 0 0 0 > 0 0 0 0 0 0 0 > 0 0 0 PCI-MSI-edge eth3-rxq3 > 81: 167 0 0 0 0 229 > 0 0 0 0 0 0 0 > 0 0 0 PCI-MSI-edge eth3-rxq4 > OK, I understand know, I have the same behaviour. >> - How can I measure performance impact (using perf, probably) of no >> balancing (ie, all on CPU0) versus balancing like explained above ? > > Yes, perf is a good tool. How would you launch it ? Using perf record and analysing the results which can be very long, or using a trick with a good command line which would help know quite instantly if IRQs are well balanced :) ? JM
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