From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934102AbYB2Vci (ORCPT ); Fri, 29 Feb 2008 16:32:38 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932407AbYB2Vc3 (ORCPT ); Fri, 29 Feb 2008 16:32:29 -0500 Received: from mx3.mail.elte.hu ([157.181.1.138]:41673 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932229AbYB2Vc2 (ORCPT ); Fri, 29 Feb 2008 16:32:28 -0500 Date: Fri, 29 Feb 2008 22:32:07 +0100 From: Ingo Molnar To: Peter Zijlstra Cc: Paul Jackson , tglx@linutronix.de, oleg@tv-sign.ru, rostedt@goodmis.org, maxk@qualcomm.com, linux-kernel@vger.kernel.org, rientjes@google.com Subject: Re: [RFC/PATCH] cpuset: cpuset irq affinities Message-ID: <20080229213207.GN27212@elte.hu> References: <20080227222103.673194000@chello.nl> <1204311351.6243.130.camel@lappy> <20080229145516.4d96aeaa.pj@sgi.com> <1204319674.6243.145.camel@lappy> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1204319674.6243.145.camel@lappy> User-Agent: Mutt/1.5.17 (2007-11-01) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Peter Zijlstra wrote: > > Could you educate me a little, Peter, on what these irqs are and on > > the sorts of ways people might want to place them across CPUs? > > I'm not sure I know what you're asking. IRQ are hardware notifiers and > do all kinds of things depending on the hardware. Network cards > typically use them to notify the CPU of incoming packets. Video cards > can do vsync notifiers, empty dma buffers, whatnot. irq affinity masks can basically be thought of as: "these are the CPUs where external hardware events will trigger certain kernel functions and cause overhead on those CPUs". An IRQ can have followup effects: softirq execution, workqueue execution, etc. so managing the IRQ masks is very meaningful and just as meaningful as managing the affinity masks of tasks. You can think of "IRQ# 123" as "special kernel task # 123". Ingo