linux-kernel - Re: [RFC PATCH] timer: Improve itimers scalability

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Message-ID: <20150805093719.GV25159@twins.programming.kicks-ass.net>
Date:	Wed, 5 Aug 2015 11:37:19 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jason Low <jason.low2@...com>
Cc:	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	Frederic Weisbecker <fweisbec@...il.com>,
	Oleg Nesterov <oleg@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Davidlohr Bueso <dave@...olabs.net>,
	Mike Galbraith <umgwanakikbuti@...il.com>, terry.rudd@...com,
	Rik van Riel <riel@...hat.com>,
	Waiman Long <Waiman.Long@...com>,
	Scott J Norton <scott.norton@...com>
Subject: Re: [RFC PATCH] timer: Improve itimers scalability

On Tue, Aug 04, 2015 at 05:29:44PM -0700, Jason Low wrote:

> @@ -1137,6 +1148,13 @@ static inline int fastpath_timer_check(struct task_struct *tsk)
>  	if (READ_ONCE(sig->cputimer.running)) {

Maybe make that:

	if (READ_ONCE(sig->cputimer.running) &&
	    !READ_ONCE(sig->cputimer.is_checking_timer)) {

>  		struct task_cputime group_sample;
>  
> +		/*
> +		 * If another thread in the group is already checking
> +		 * for the thread group cputimer, then we will skip that.
> +		 */
> +		if (READ_ONCE(sig->cputimer.is_checking_timer))
> +			return 0;
> +
>  		sample_cputime_atomic(&group_sample, &sig->cputimer.cputime_atomic);
>  
>  		if (task_cputime_expired(&group_sample, &sig->cputime_expires))


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