linux-kernel - Re: [patch 44/44] posix-cpu-timers: Expire timers directly

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Message-ID: <alpine.DEB.2.21.1908201507100.2223@nanos.tec.linutronix.de>
Date:   Tue, 20 Aug 2019 15:07:36 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
cc:     Oleg Nesterov <oleg@...hat.com>, Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        John Stultz <john.stultz@...aro.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Anna-Maria Behnsen <anna-maria@...utronix.de>
Subject: Re: [patch 44/44] posix-cpu-timers: Expire timers directly

On Mon, 19 Aug 2019, Thomas Gleixner wrote:

> Moving the posix cpu timers from on list to another and then expiring them
> from the second list is avoiding to drop and reacquire sighand lock for
> each timer expiry, but on the other hand it's more complicated code and
> suboptimal for a small number of timers.
> 
> Remove the extra list and expire them directly from the rbtree. Tests with
> a large number of timers did not show a difference outside of the noise
> range.
> 
> This also allows to switch the crude heuristics of limiting the expiry of
> timers to 20 for each type to a time based limitation which is way more
> sensible.

This one is buggy. I know why so don't waste your time reviewing it.