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

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Message-ID: <20090223110725.GB17312@elte.hu>
Date:	Mon, 23 Feb 2009 12:07:25 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>
Cc:	Balbir Singh <balbir@...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


* 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.

	Ingo
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