linux-kernel - Re: [PATCH 1/1] cputime: Make the reported utime+stime correspond to the actual runtime.

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Message-ID: <1435615884.21928.57.camel@j-VirtualBox>
Date:	Mon, 29 Jun 2015 15:11:24 -0700
From:	Jason Low <jason.low2@...com>
To:	Fredrik Markström <fredrik.markstrom@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, mingo@...hat.com,
	linux-kernel@...r.kernel.org, Rik van Riel <riel@...hat.com>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	jason.low2@...com
Subject: Re: [PATCH 1/1] cputime: Make the reported utime+stime correspond
 to the actual runtime.

On Mon, 2015-06-29 at 21:08 +0200, Fredrik Markström wrote:
> I don't think that is good enough. I believe the reason the
> max()-stuff was initially put there to make sure the returned stime
> and utime components are increasing monotonically. The scaling code
> can cause either or to decrease from one call to the other even i
> rtime increases.
> 
> The purpose of my patch is to also make sure that the sum of utime and
> stime is rtime.
> 
> I lost the last part of the patch in my previous email:
> 
> 
> -       cputime_advance(&prev->stime, stime);
> -       cputime_advance(&prev->utime, utime);
> +       if (stime < prev->stime) {
> +               stime = prev->stime;
> +               utime = rtime - stime;
> +       } else if (utime < prev->utime) {
> +               utime = prev->utime;
> +               stime = rtime - utime;
> +       }
> -out:
> +       if (prev->stime + prev->utime < rtime) {
> +               prev->stime = stime;
> +               prev->utime = utime;
> +       }
>         *ut = prev->utime;
>         *st = prev->stime;

In this case, we might want to avoid the extra stime and utime
computations if prev->stime + prev->utime >= rtime, since they wouldn't
get used.

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