linux-kernel - Re: [patch V2 34/38] posix-cpu-timers: Get rid of 64bit divisions

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Date:   Tue, 27 Aug 2019 00:51:13 +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 34/38] posix-cpu-timers: Get rid of 64bit divisions

On Wed, Aug 21, 2019 at 09:09:21PM +0200, Thomas Gleixner wrote:
> Instead of dividing A to match the units of B it's more efficient to
> multiply B to match the units of A.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
> V2: Fix the dropped update of the expiry cache when the soft limit increased
> ---
>  kernel/time/posix-cpu-timers.c |   24 ++++++++++++++----------
>  1 file changed, 14 insertions(+), 10 deletions(-)
> 
> --- a/kernel/time/posix-cpu-timers.c
> +++ b/kernel/time/posix-cpu-timers.c
> @@ -798,10 +798,11 @@ static void check_thread_timers(struct t
>  	 */
>  	soft = task_rlimit(tsk, RLIMIT_RTTIME);
>  	if (soft != RLIM_INFINITY) {
> +		/* Task RT timeout is accounted in jiffies. RTTIME is usec */
> +		unsigned long rtim = tsk->rt.timeout * (USEC_PER_SEC / HZ);

jiffies_to_usecs() ?

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