linux-kernel - Re: [PATCH 2/6] posix-cpu-timers: Don't start process wide cputime counter if timer is disabled

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Date:   Wed, 16 Jun 2021 13:50:32 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Oleg Nesterov <oleg@...hat.com>, Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 2/6] posix-cpu-timers: Don't start process wide cputime
 counter if timer is disabled

On Wed, Jun 16, 2021 at 01:26:30PM +0200, Peter Zijlstra wrote:
> Right, so by the time patch #5 comes around, you seem to be at the point
> where you can do:
> 
>  * fetch cputime and start threadgroup counter
> 
>  * possibly arm timer

- possibly

> 
>  * if expired:
>    - fire now
>    - if armed, disarm (which leads to stop)
> 
> Which is the other 'obvious' solution to not starting it.

So we unconditionally start and arm, and then have the early expire do
the same things as regular expire.