Re: [tip:sched/core] sched: cpuacct: Use bigger percpu counter batch values for stats counters

KAMEZAWA Hiroyuki
2009-08-21T06:23:55Z

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.
>

Ok, I reproduced it on ia64 box (ia64 supports VIRT_CPU_ACCOUNTING)

On 8cpu
-- config=on--
procs -----------memory---------- ---swap-- -----io---- --system-- -----cpu------
r b swpd free buff cache si so bi bo in cs us sy id wa st
11 0 0 7185152 66048 284416 0 0 0 0 5918 12354 0 100 0 0 0
--config=off--
11 0 0 7194496 66304 283392 0 0 0 20 8023 1424022 32 68 0 0 0

Wow, yes. 100x regression.

I'll dig this more.

IIUC, If CONFIG_VIRT_CPU_ACCOUNTING=on, process's stime/utime records "nanosecond".
Then, batch=32 is too small. How about once per msec ?

Thanks,
-Kame