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

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Date:	Wed, 05 Aug 2015 12:44:41 -0700
From:	Jason Low <jason.low2@...com>
To:	Peter Zijlstra <peterz@...radead.org>
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>, jason.low2@...com
Subject: Re: [RFC PATCH] timer: Improve itimers scalability

On Wed, 2015-08-05 at 11:37 +0200, Peter Zijlstra wrote:
> 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)) {

Yes, I think it would be better if the check is done here.

And perhaps the comment can be modified to:

/*
 * Check if thread group timers expired. This is skipped if the cputimer
 * is not running or if another thread in the group is already checking
 * for thread group cputimers.
 */

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