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Date: Fri, 26 Sep 2014 00:27:10 -0400 (EDT) From: David Miller <davem@...emloft.net> To: eric.dumazet@...il.com Cc: netdev@...r.kernel.org Subject: Re: [PATCH net-next] net: sched: use pinned timers From: Eric Dumazet <eric.dumazet@...il.com> Date: Sat, 20 Sep 2014 18:01:30 -0700 > From: Eric Dumazet <edumazet@...gle.com> > > While using a MQ + NETEM setup, I had confirmation that the default > timer migration ( /proc/sys/kernel/timer_migration ) is killing us. > > Installing this on a receiver side of a TCP_STREAM test, (NIC has 8 TX > queues) : ... > We can see that timers get migrated into a single cpu, presumably idle > at the time timers are set up. > Then all qdisc dequeues run from this cpu and huge lock contention > happens. This single cpu is stuck in softirq mode and cannot dequeue > fast enough. > > 39.24% [kernel] [k] _raw_spin_lock > 2.65% [kernel] [k] netem_enqueue > 1.80% [kernel] [k] netem_dequeue > 1.63% [kernel] [k] copy_user_enhanced_fast_string > 1.45% [kernel] [k] _raw_spin_lock_bh > > By pinning qdisc timers on the cpu running the qdisc, we respect proper > XPS setting and remove this lock contention. > > 5.84% [kernel] [k] netem_enqueue > 4.83% [kernel] [k] _raw_spin_lock > 2.92% [kernel] [k] copy_user_enhanced_fast_string > > Current Qdiscs that benefit from this change are : > > netem, cbq, fq, hfsc, tbf, htb. > > Signed-off-by: Eric Dumazet <edumazet@...gle.com> Looks great, applied, thanks Eric. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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