Re: [PATCH v2] sched/cputime: Don't account idle time twice after dyntick-idle

[Stian Halseth]

On Tue, 2026-10-06 at 13:08 +0200, Frederic Weisbecker wrote:

> > Only with steal time, and that is older than the rework. I ran the
> > same
> > guest test on v7.1 and on ad5a9e14ec8b, the parent of
> > cf6444c3e1bb7.
> > Total CPU time per wall second on the loaded vCPU:
> > 
> >                           v7.1    ad5a9e14ec8b   v2
> >   3.7 ms sleeps           0.995   0.996          0.998
> >   pipe ping-pong          0.997   0.996          1.000
> >   steal, sleep + spin     1.029   1.028          1.008
> >   steal, pipe ping-pong   1.338   1.341          1.001
> > 
> > Without steal time nothing was counted twice before the rework.
> > With
> > steal time, v7.1 counted steal time during idle as both idle and
> > steal
> > time. The rework fixed most of that, and what is left with a busy
> > spin
> > after each wakeup is smaller than before.
> 
> Ok and you haven't observed a real difference between your v1 and v2,
> right?
> 
No, not in normal operation. 

It only made a difference with a test-only change that stops the tick
on every idle entry. There v2 added to a pending overlap about 900
times a second, which v1 lost.

/Stian

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