Re: [PATCH] better align percpu counter (Was Re: [tip:sched/core] sched: cpuacct: Use bigger percpu counter batch values for stats counters

[Ingo Molnar <mingo@elte.hu>]

* KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:

> On Thu, 20 Aug 2009 16:24:51 +1000
> Anton Blanchard <anton@samba.org> wrote:
> 
> >  
> > Hi,
> > 
> > > Could you share contex-switch-test program ?
> > > I'd like to play with it to find out what I can do against percpu counter.
> > 
> > Sure:
> > 
> > http://ozlabs.org/~anton/junkcode/context_switch.c
> > 
> > Very simple, just run it once per core:
> > 
> > for i in `seq 0 31`
> > do
> > 	taskset -c $i ./context_switch &
> > done
> > 
> > Then look at the context switch rates in vmstat.
> > 
> Thank you for test program.
> 
> Before adjusting batch counter (I think you should modify it),
> Could you try this ?
> 
> I only have 8cpu(2socket) host but works well.
> (But...my host is x86-64 and has not virt-cpu-accouting.)
> 
> with your program
> before patch.
> cpuacct off : 414000-416000 ctsw per sec.
> cpuacct on  : 401000-404000 ctsw per sec.
> 
> after patch
> cpuacct on  : 412000-413000 ctsw per sec.
> 
> Maybe I should check cache-miss late ;)

Btw., in latest upstream you can do that via:

  cd tools/perf/
  make -j install

  perf stat --repeat 5 -- taskset -c 1 ./context_switch

there will be cache-miss and other stats, error bars so 
you can compare the before/after better, etc.

	Ingo