linux-kernel - Re: [PATCH] sched/cputime: make scale

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Message-ID: <20190723142918.GC8994@redhat.com>
Date:   Tue, 23 Jul 2019 16:29:18 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Fox <afox@...hat.com>,
        Stephen Johnston <sjohnsto@...hat.com>,
        linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Stanislaw Gruszka <sgruszka@...hat.com>
Subject: Re: [PATCH] sched/cputime: make scale_stime() more precise

On 07/23, Oleg Nesterov wrote:
>
> > > Yes, statistically the numbers are proportionally divided.
> >
> > This; due to the loss in precision the distribution is like a step
> > function around the actual s:u ratio line, but on average it still is
> > s:u.
>
> You know, I am no longer sure... perhaps it is even worse, I need to recheck.

To clarify, this is probably true even if prev_cputime adds more confusion.
But how many minutes (hours? days?) you need to look at /proc/pid/stat
to get the average which more or less matches the reality?

Oleg.