Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S263429AbUILWZp (ORCPT ); Sun, 12 Sep 2004 18:25:45 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263540AbUILWZp (ORCPT ); Sun, 12 Sep 2004 18:25:45 -0400 Received: from viper.oldcity.dca.net ([216.158.38.4]:56714 "HELO viper.oldcity.dca.net") by vger.kernel.org with SMTP id S263429AbUILWZn (ORCPT ); Sun, 12 Sep 2004 18:25:43 -0400 Subject: Re: [PATCH 1/3] Separate IRQ-stacks from 4K-stacks option From: Lee Revell To: Andrea Arcangeli Cc: Ingo Molnar , Chris Wedgwood , Arjan van de Ven , Hugh Dickins , "Martin J. Bligh" , Alan Cox , LKML , Christoph Hellwig In-Reply-To: <20040912220720.GC3049@dualathlon.random> References: <593560000.1094826651@[10.10.2.4]> <20040910151538.GA24434@devserv.devel.redhat.com> <20040910152852.GC15643@x30.random> <20040910153421.GD24434@devserv.devel.redhat.com> <1095016687.1306.667.camel@krustophenia.net> <20040912192515.GA8165@taniwha.stupidest.org> <20040912193542.GB28791@elte.hu> <20040912203308.GA3049@dualathlon.random> <1095025000.22893.52.camel@krustophenia.net> <20040912220720.GC3049@dualathlon.random> Content-Type: text/plain Message-Id: <1095027951.22893.69.camel@krustophenia.net> Mime-Version: 1.0 X-Mailer: Ximian Evolution 1.4.6 Date: Sun, 12 Sep 2004 18:25:51 -0400 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1339 Lines: 28 On Sun, 2004-09-12 at 18:07, Andrea Arcangeli wrote: > On Sun, Sep 12, 2004 at 05:36:41PM -0400, Lee Revell wrote: > > But in this case the hardirq handler can run for 2ms, which caused a > > scheduler latency problem, because nothing could run but other IRQs. > > The IRQ threading in Ingo's patches solves the problem, and seems to me > > to be the correct solution. > > the irq threading must have a cost, doesn't it? I doubt you want to > offload irqs to a kernel thread on a server, *that* would be slow (irq > nesting is zerocost compared to scheduling a kernel thread). Yes, on a server you would probably disable threading for the disk and network IRQs (the VP patch lets you set this via /proc). This feature effectively gives you IPLs on Linux, albeit only two of them. For example to prevent heavy traffic on one network interface from impacting the latency of the other, you could enable threading for the first and disable it for the second. I am still unsure why the IDE i/o completion is the one place that breaks the assumption that hardirq handlers execute quickly. Lee - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/