Re: [PATCH] sched/cputime: Ensure correct utime and stime proportion

From: Xunlei Pang
Date: Thu Jul 05 2018 - 09:21:28 EST

On 7/5/18 6:46 PM, Peter Zijlstra wrote:
> On Wed, Jun 27, 2018 at 08:22:42PM +0800, Xunlei Pang wrote:
>> tick-based whole utime is utime_0, tick-based whole stime
>> is stime_0, scheduler time is rtime_0.
>> For a long time, the process runs mainly in userspace with
>> run-sleep patterns, and because two different clocks, it
>> is possible to have the following condition:
>> rtime_0 < utime_0 (as with little stime_0)
> I don't follow... what?
> Why are you, and why do you think it makes sense to, compare rtime_0
> against utime_0 ?
> The [us]time_0 are, per your earlier definition, ticks. They're not an
> actual measure of time. Do not compare the two, that makes no bloody
> sense.

[us]time_0 is task_struct:utime{stime}, I cited directly from
cputime_adjust(), both in nanoseconds. I assumed "rtime_0 < utime_0"
here to simple the following proof to help explain the problem we met.