linux-kernel - Re: [RFC PATCH 02/15] nohz_task: Avoid nohz task cpu as non-idle timer target

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Message-ID: <1292861202.22905.23.camel@gandalf.stny.rr.com>
Date:	Mon, 20 Dec 2010 11:06:42 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Anton Blanchard <anton@....ibm.com>,
	Tim Pepper <lnxninja@...ux.vnet.ibm.com>
Subject: Re: [RFC PATCH 02/15] nohz_task: Avoid nohz task cpu as non-idle
 timer target

On Mon, 2010-12-20 at 16:47 +0100, Peter Zijlstra wrote:
> On Mon, 2010-12-20 at 16:24 +0100, Frederic Weisbecker wrote:
> > Unbound timers are preferably targeted for non idle cpu. If
> > possible though, prioritize idle cpus over nohz task cpus,
> > because the main point of nohz task is to avoid unnecessary
> > timer interrupts.
> 
> Oh is it?
> 
> I'd very much expect the cpu that arms the timer to get the interrupt. I
> mean, if the task doesn't want to get interrupted by timers,
> _DON'T_USE_TIMERS_ to begin with.
> 
> So no, don't much like this at all.

I think this comes from other tasks on other CPUs that are using timers.
Although, I'm not sure what causes an "unbound" timer to happen. I
thought timers usually go off on the CPU that asked for it to go off.

-- Steve


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