linux-kernel - Re: [PATCH] cpuacct: VIRT_CPU_ACCOUNTING don't prevent percpu cputime count

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Date:	Wed, 29 Apr 2009 11:26:30 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	balbir@...ux.vnet.ibm.com
Cc:	kosaki.motohiro@...fujitsu.com,
	LKML <linux-kernel@...r.kernel.org>,
	Bharata B Rao <bharata@...ux.vnet.ibm.com>,
	Balaji Rao <balajirrao@...il.com>,
	Dhaval Giani <dhaval@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	seto.hidetoshi@...fujitsu.com
Subject: Re: [PATCH] cpuacct: VIRT_CPU_ACCOUNTING don't prevent percpu cputime count

Hi

Thanks for reviewing.

> >  /* return cpu accounting group corresponding to this container */
> >  static inline struct cpuacct *cgroup_ca(struct cgroup *cgrp)
> > @@ -10146,6 +10147,9 @@ static struct cgroup_subsys_state *cpuac
> >  	if (!ca->cpuusage)
> >  		goto out_free_ca;
> > 
> > +	if (!cpuacct_batch)
> > +		cpuacct_batch = jiffies_to_cputime(percpu_counter_batch);
> > +
> 
> I expect cpuacct_batch to be a large number

Yes.


> 
> >  	for (i = 0; i < CPUACCT_STAT_NSTATS; i++)
> >  		if (percpu_counter_init(&ca->cpustat[i], 0))
> >  			goto out_free_counters;
> > @@ -10342,7 +10346,7 @@ static void cpuacct_update_stats(struct 
> >  	ca = task_ca(tsk);
> > 
> >  	do {
> > -		percpu_counter_add(&ca->cpustat[idx], val);
> > +		__percpu_counter_add(&ca->cpustat[idx], val, cpuacct_batch);
> 
> This will make the end result very off the real value due to large
> batch value per cpu. If we are going to go this route, we should
> probably consider using __percpu_counter_sum so that the batch value
> does not show data that is way off.

No problem.

end-user don't see cputime itself. they see converted time.
cpuacct_stats_show() use cputime64_to_clock_t. it mean
the value less than 10msec don't display.

--------------------------------------------------------
static int cpuacct_stats_show(struct cgroup *cgrp, struct cftype *cft,
                struct cgroup_map_cb *cb)
{
        struct cpuacct *ca = cgroup_ca(cgrp);
        int i;

        for (i = 0; i < CPUACCT_STAT_NSTATS; i++) {
                s64 val = percpu_counter_read(&ca->cpustat[i]);
                val = cputime64_to_clock_t(val);
                cb->fill(cb, cpuacct_stat_desc[i], val);
        }
        return 0;
}
--------------------------------------------------------





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