linux-kernel - Re: [PATCH 09/12] irq: implement IRQ expecting

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Message-ID: <20100617090229.543af62c@infradead.org>
Date:	Thu, 17 Jun 2010 09:02:29 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Tejun Heo <tj@...nel.org>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>, mingo@...e.hu,
	bphilips@...e.de, yinghai@...nel.org, akpm@...ux-foundation.org,
	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
	jeff@...zik.org, linux-ide@...r.kernel.org,
	stern@...land.harvard.edu, gregkh@...e.de, khali@...ux-fr.org
Subject: Re: [PATCH 09/12] irq: implement IRQ expecting

On Thu, 17 Jun 2010 17:54:48 +0200
Tejun Heo <tj@...nel.org> wrote:

> Crazy devices too but I think they would
> fall in a single tick any way. 

not sure what ticks have to do with anything but ok ;)

> At any rate, let's say I have those
> numbers, how would I feed it into c-state selection?

if we have this, we need to put a bit of glue in the backend that
tracks (per cpu I suppose) the shortest expected interrupt, which
the C state code then queries.
(and in that regard, it does not matter if shortest expected is
computed via heuristic on a per irq basis, or passed in).

mapping an irq to a cpu is not a 100% science (since interrupts can
move in theory), but just assuming that the irq will happen on the same
CPU it happened last time is more than good enough.


-- 
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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