From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: [PATCH 09/12] irq: implement IRQ expecting Date: Thu, 17 Jun 2010 18:47:19 +0200 Message-ID: <4C1A5197.8060409@kernel.org> References: <1276443098-20653-1-git-send-email-tj@kernel.org> <1276443098-20653-10-git-send-email-tj@kernel.org> <20100616204854.4b036f87@infradead.org> <4C19DA64.8000409@kernel.org> <4C1A05AF.5010405@kernel.org> <20100617124343.5889067c@lxorguk.ukuu.org.uk> <4C1A4548.3020602@kernel.org> <20100617090229.543af62c@infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from hera.kernel.org ([140.211.167.34]:35353 "EHLO hera.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756871Ab0FQQsm (ORCPT ); Thu, 17 Jun 2010 12:48:42 -0400 In-Reply-To: <20100617090229.543af62c@infradead.org> Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Arjan van de Ven Cc: Alan Cox , Thomas Gleixner , mingo@elte.hu, bphilips@suse.de, yinghai@kernel.org, akpm@linux-foundation.org, torvalds@linux-foundation.org, linux-kernel@vger.kernel.org, jeff@garzik.org, linux-ide@vger.kernel.org, stern@rowland.harvard.edu, gregkh@suse.de, khali@linux-fr.org On 06/17/2010 06:02 PM, Arjan van de Ven wrote: > On Thu, 17 Jun 2010 17:54:48 +0200 > Tejun Heo 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 ;) Eh... right, I was thinking about something else. IRQ expect code originally had a tick based duration estimator to determine poll interval which I ripped out later for simpler stepped adjustments. c-state would need higher frequency timing measurements than jiffies. >> 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. Hmmm... the thing is that there will be many cases which won't fit irq_expect() model (why irq_watch() exists in the first place) and for the time being libata is the only one providing that data. Would the data still be useful to determine which c-state to use? Thanks. -- tejun