linux-kernel - Re: Decreasing stime running confuses top

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Date:	Thu, 04 Oct 2007 16:21:02 -0400
From:	Chuck Ebbert <cebbert@...hat.com>
To:	Christian Borntraeger <borntraeger@...ibm.com>
CC:	Luca Tettamanti <kronos.it@...il.com>,
	Frans Pop <elendil@...net.nl>, Willy Tarreau <w@....eu>,
	LKML <linux-kernel@...r.kernel.org>,
	Ilpo Järvinen <ilpo.jarvinen@...sinki.fi>,
	"Alexander E. Patrakov" <patrakov@....usu.ru>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: Decreasing stime running confuses top

On 10/04/2007 04:00 PM, Christian Borntraeger wrote:
> Am Donnerstag, 4. Oktober 2007 schrieb Chuck Ebbert:
>> Is CONFIG_VIRT_CPU_ACCOUNTING set?
> 
> This is s390 and powerpc only, so the answer is probably no ;-)
> 

The code in fs/proc/array.c is... interesting.

1. task_stime() converts p->se.sum_exec_runtime to a clock_t

2. it calls task_utime() which does the same thing (can it change
   between the two reads?), does some calculations that yield a 
   clock_t, turns the result into a cputime and returns that

3. task_stime() then converts that result back into a clock_t and
   uses it!


static cputime_t task_stime(struct task_struct *p)
{
        clock_t stime;

        stime = nsec_to_clock_t(p->se.sum_exec_runtime) -
                        cputime_to_clock_t(task_utime(p));

        return clock_t_to_cputime(stime);
}

static cputime_t task_utime(struct task_struct *p)
{
        clock_t utime = cputime_to_clock_t(p->utime),
                total = utime + cputime_to_clock_t(p->stime);
        u64 temp;

        temp = (u64)nsec_to_clock_t(p->se.sum_exec_runtime);

        if (total) {
                temp *= utime;
                do_div(temp, total);
        }
        utime = (clock_t)temp;

        return clock_t_to_cputime(utime);
}
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