Message-ID: <1435604090.21928.19.camel@j-VirtualBox>
Subject: Re: [PATCH 1/1] cputime: Make the reported utime+stime correspond
 to the actual runtime.
From: Jason Low <jason.low2@hp.com>
To: Fredrik =?ISO-8859-1?Q?Markstr=F6m?= <fredrik.markstrom@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>, mingo@redhat.com,
        linux-kernel@vger.kernel.org, Rik van Riel <riel@redhat.com>,
        =?ISO-8859-1?Q?Fr=E9d=E9ric?= Weisbecker <fweisbec@gmail.com>,
        jason.low2@hp.com
Date: Mon, 29 Jun 2015 11:54:50 -0700
In-Reply-To: <CAKdL+dRPEenCzi14SWypOv6Vv+x2X0bHQXXc-G6gqUT+VhOtUw@mail.gmail.com>
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	 <1434104217.1495.74.camel@twins>
	 <20150612110158.GA18673@twins.programming.kicks-ass.net>
	 <CAKdL+dQWGtzURUe+4cB4XtsoaEPh0p0O1ejzbgxN0AUsbvUi0g@mail.gmail.com>
	 <20150629145837.GE3644@twins.programming.kicks-ass.net>
	 <CAKdL+dRPEenCzi14SWypOv6Vv+x2X0bHQXXc-G6gqUT+VhOtUw@mail.gmail.com>
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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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