linux-kernel - Re: [RFC PATCH 0/4] timers: framework for migration between CPU

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Message-ID: <20090220115745.43d202d6@infradead.org>
Date:	Fri, 20 Feb 2009 11:57:45 -0800
From:	Arjan van de Ven <arjan@...radead.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, linux-pm@...ts.linux-foundation.org,
	a.p.zijlstra@...llo.nl, ego@...ibm.com, tglx@...utronix.de,
	andi@...stfloor.org, venkatesh.pallipadi@...el.com,
	vatsa@...ux.vnet.ibm.com, arun@...ux.vnet.ibm.com,
	Suresh Siddha <suresh.b.siddha@...el.com>
Subject: Re: [RFC PATCH 0/4] timers: framework for migration between CPU

On Fri, 20 Feb 2009 17:07:37 +0100
Ingo Molnar <mingo@...e.hu> wrote:

> 
> * Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com> wrote:
> 
> > > I'd also suggest to not do that rather ugly 
> > > enable_timer_migration per-cpu variable, but simply reuse 
> > > the existing nohz.load_balancer as a target CPU.
> > 
> > This is a good idea to automatically bias the timers.  But 
> > this nohz.load_balancer is a very fast moving target and we 
> > will need some heuristics to estimate overall system idleness 
> > before moving the timers.
> > 
> > I would agree that the power saving load balancer has a good 
> > view of the system and can potentially guide the timer biasing 
> > framework.
> 
> Yeah, it's a fast moving target, but it already concentrates 
> the load somewhat.
> 

I wonder if the real answer for this isn't to have timers be considered 
schedulable-entities and have the regular scheduler decide where they
actually run.

-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
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