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

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Message-ID: <20090220215318.GA30665@elte.hu>
Date:	Fri, 20 Feb 2009 22:53:18 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Arjan van de Ven <arjan@...radead.org>
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


* Arjan van de Ven <arjan@...radead.org> wrote:

> 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.

hm, not sure - it's a bit heavy for that.

	Ingo
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