linux-kernel - Re: [PATCH 1/3] timer: Optimize fastpath_timer

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Date:	Wed, 26 Aug 2015 23:57:59 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Jason Low <jason.low2@...com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Oleg Nesterov <oleg@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Davidlohr Bueso <dave@...olabs.net>,
	Steven Rostedt <rostedt@...dmis.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Terry Rudd <terry.rudd@...com>, Rik van Riel <riel@...hat.com>,
	Scott J Norton <scott.norton@...com>
Subject: Re: [PATCH 1/3] timer: Optimize fastpath_timer_check()

On Tue, Aug 25, 2015 at 08:17:46PM -0700, Jason Low wrote:
> In fastpath_timer_check(), the task_cputime() function is always
> called to compute the utime and stime values. However, this is not
> necessary if there are no per-thread timers to check for. This patch
> modifies the code such that we compute the task_cputime values only
> when there are per-thread timers set.
> 
> Signed-off-by: Jason Low <jason.low2@...com>

Reviewed-by: Frederic Weisbecker <fweisbec@...il.com>

Thanks.

> ---
>  kernel/time/posix-cpu-timers.c |   15 +++++++--------
>  1 files changed, 7 insertions(+), 8 deletions(-)
> 
> diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c
> index 892e3da..02596ff 100644
> --- a/kernel/time/posix-cpu-timers.c
> +++ b/kernel/time/posix-cpu-timers.c
> @@ -1117,16 +1117,15 @@ static inline int task_cputime_expired(const struct task_cputime *sample,
>  static inline int fastpath_timer_check(struct task_struct *tsk)
>  {
>  	struct signal_struct *sig;
> -	cputime_t utime, stime;
> -
> -	task_cputime(tsk, &utime, &stime);
>  
>  	if (!task_cputime_zero(&tsk->cputime_expires)) {
> -		struct task_cputime task_sample = {
> -			.utime = utime,
> -			.stime = stime,
> -			.sum_exec_runtime = tsk->se.sum_exec_runtime
> -		};
> +		struct task_cputime task_sample;
> +		cputime_t utime, stime;
> +
> +		task_cputime(tsk, &utime, &stime);
> +		task_sample.utime = utime;
> +		task_sample.stime = stime;
> +		task_sample.sum_exec_runtime = tsk->se.sum_exec_runtime;
>  
>  		if (task_cputime_expired(&task_sample, &tsk->cputime_expires))
>  			return 1;
> -- 
> 1.7.2.5
> 
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