linux-kernel - Re: [patch V2 32/38] posix-cpu-timers: Get rid of zero checks

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Date:   Mon, 26 Aug 2019 23:57:18 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Oleg Nesterov <oleg@...hat.com>,
        Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        John Stultz <john.stultz@...aro.org>,
        Anna-Maria Behnsen <anna-maria@...utronix.de>,
        Christoph Hellwig <hch@....de>
Subject: Re: [patch V2 32/38] posix-cpu-timers: Get rid of zero checks

On Wed, Aug 21, 2019 at 09:09:19PM +0200, Thomas Gleixner wrote:
> Deactivation of the expiry cache is done by setting all clock caches to
> 0. That requires to have a check for zero in all places which update the
> expiry cache:
> 
> 	if (cache == 0 || new < cache)
> 		cache = new;
> 
> Use U64_MAX as the deactivated value, which allows to remove the zero
> checks when updating the cache and reduces it to the obvious check:
> 
> 	if (new < cache)
> 		cache = new;
> 
> This also removes the weird workaround in do_prlimit() which was required
> to convert a RLIMIT_CPU value of 0 (immediate expiry) to 1 because handing
> in 0 to the posix CPU timer code would have effectively disarmed it.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

Reviewed-by: Frederic Weisbecker <frederic@...nel.org>