linux-kernel - Re: Rescheduling interrupts

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Date:	Tue, 22 Jan 2008 20:27:44 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Matt Mackall <mpm@...enic.com>
Cc:	S.Çağlar Onur <caglar@...dus.org.tr>,
	LKML <linux-kernel@...r.kernel.org>,
	Arjan van de Ven <arjan@...ux.intel.com>
Subject: Re: Rescheduling interrupts

* Matt Mackall <mpm@...enic.com> wrote:

> > amarokapp does wake up threads every 20 microseconds - that could 
> > explain it. It's probably Xorg running on one core, amarokapp on the 
> > other core. That's already 100 reschedules/sec.
> 
> That suggests we want an "anti-load-balancing" heuristic when CPU 
> usage is very low. Migrating everything onto one core when we're close 
> to idle will save power and probably reduce latencies.

that would probably be the case if it's multiple sockets - but for 
multiple cores exactly the opposite is true: the sooner _both_ cores 
finish processing, the deeper power use the CPU can reach. So effective 
and immediate spreading of workloads amongst multiple cores - especially 
with shared L2 caches where the cost of migration is low, helps power 
consumption. (and it obviously helps latencies and bandwith)

	Ingo
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