Messages in this thread | | | Date | Thu, 20 Aug 2009 15:10:38 +1000 | From | Anton Blanchard <> | Subject | Re: [tip:sched/core] sched: cpuacct: Use bigger percpu counter batch values for stats counters |
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Hi,
Looks like this issue is still present. I tested on a 32 core box and the patch improved maximum context switch rate from from 76k/sec to 9.5M/sec. Thats over 100x faster, or 50x per line of code. That's got to be some sort of record :)
Any chance we can get a fix in for 2.6.31? Don't make me find an even bigger box so I can break the 200x mark :)
Anton
> -- > > When CONFIG_VIRT_CPU_ACCOUNTING is enabled we can call cpuacct_update_stats > with values much larger than percpu_counter_batch. This means the > call to percpu_counter_add will always add to the global count which is > protected by a spinlock. > > Since reading of the CPU accounting cgroup counters is not performance > critical, we can use a maximum size batch of INT_MAX and use > percpu_counter_sum on the read side which will add all the percpu > counters. > > With this patch an 8 core POWER6 with CONFIG_VIRT_CPU_ACCOUNTING and > CONFIG_CGROUP_CPUACCT shows an improvement in aggregate context switch rate of > 397k/sec to 3.9M/sec, a 10x improvement. > > Signed-off-by: Anton Blanchard <anton@samba.org> > --- > > Index: linux.trees.git/kernel/sched.c > =================================================================== > --- linux.trees.git.orig/kernel/sched.c 2009-07-16 10:11:02.000000000 +1000 > +++ linux.trees.git/kernel/sched.c 2009-07-16 10:16:41.000000000 +1000 > @@ -10551,7 +10551,7 @@ > int i; > > for (i = 0; i < CPUACCT_STAT_NSTATS; i++) { > - s64 val = percpu_counter_read(&ca->cpustat[i]); > + s64 val = percpu_counter_sum(&ca->cpustat[i]); > val = cputime64_to_clock_t(val); > cb->fill(cb, cpuacct_stat_desc[i], val); > } > @@ -10621,7 +10621,7 @@ > ca = task_ca(tsk); > > do { > - percpu_counter_add(&ca->cpustat[idx], val); > + __percpu_counter_add(&ca->cpustat[idx], val, INT_MAX); > ca = ca->parent; > } while (ca); > rcu_read_unlock();
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