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

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Date:	Mon, 29 Jun 2015 11:54:50 -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 17:28 +0200, Fredrik Markström wrote:
> Hello Peter, the locking part looks good, I don't have a strong
> opinion on per task/signal lock vs global lock.
> 
> But with the patch we still update prev->utime and prev->stime
> independently, which was the original problem.  But maybe the locking
> and monoticity/sum issue should be addressed by two separate patches
> since they are separate bugs ?
> 
> The part I'm referring to is the change below from my original patch
> (maybe without the WARN_ON:s ?):
> 
> …
> -       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;
> +       }
> +       WARN_ON(stime < prev->stime);
> +       WARN_ON(utime < prev->utime);
> +       WARN_ON(stime + utime != rtime);

How about substituting:

	prev->stime = max(prev->stime, stime);
	prev->utime = max(prev->utime, utime);

with

        if (stime > prev->stime || utime > prev->utime) {
		prev->stime = stime;
		prev->utime = utime;
	}

in Peter's patch?

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