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

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Message-ID: <20090223112517.GD10226@balbir.in.ibm.com>
Date:	Mon, 23 Feb 2009 16:55:17 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Arjan van de Ven <arjan@...radead.org>,
	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

* Ingo Molnar <mingo@...e.hu> [2009-02-23 12:07:25]:

> 
> * Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com> wrote:
> 
> > My understanding is that we will certainly have a sysfs 
> > tunable to 'enable' timer migration or consolidation, similar 
> > to the sched_mc=2 policy, but the actual set of CPUs to 
> > evacuate and the correct set of target CPUs to consolidate 
> > should come from the scheduler and not necessarily from the 
> > user space.
> 
> Yes.
> 
> > The scheduler should be able to figure out the following 
> > parameters:
> > 
> > * Identify set of idle CPUs (CPU package) from which timers 
> >   can be removed
> > * Identify a semi-idle or idle CPU package to which the timers
> >   can be moved
> > * Decide when to start moving timers as the system has large
> >   number of idle CPUs
> > * Decide when to stop migrating as system becomes less idle
> >   and utilisation increases
> > 
> > Guiding all of the above decisions from user space may not be 
> > fast enough.
> 
> Exactly.
>

OK, lets head that way for now. I've highlighted my concerns in a
different email. Experimentation will definitely show us if they are
justified or not. 

-- 
	Balbir
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