Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261405AbUILUcI (ORCPT ); Sun, 12 Sep 2004 16:32:08 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261426AbUILUcI (ORCPT ); Sun, 12 Sep 2004 16:32:08 -0400 Received: from mail-relay-2.tiscali.it ([213.205.33.42]:18601 "EHLO mail-relay-2.tiscali.it") by vger.kernel.org with ESMTP id S261405AbUILUcF (ORCPT ); Sun, 12 Sep 2004 16:32:05 -0400 Date: Sun, 12 Sep 2004 22:33:08 +0200 From: Andrea Arcangeli To: Ingo Molnar Cc: Chris Wedgwood , Lee Revell , Arjan van de Ven , Hugh Dickins , "Martin J. Bligh" , Alan Cox , LKML , Christoph Hellwig Subject: Re: [PATCH 1/3] Separate IRQ-stacks from 4K-stacks option Message-ID: <20040912203308.GA3049@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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20040912193542.GB28791@elte.hu> X-GPG-Key: 1024D/68B9CB43 13D9 8355 295F 4823 7C49 C012 DFA1 686E 68B9 CB43 X-PGP-Key: 1024R/CB4660B9 CC A0 71 81 F4 A0 63 AC C0 4B 81 1D 8C 15 C8 E5 User-Agent: Mutt/1.5.6i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1119 Lines: 26 On Sun, Sep 12, 2004 at 09:35:42PM +0200, Ingo Molnar wrote: > no. A 2 msec nonpreemptable delay is a 2 msec delay, irqs on or off > alike. irq-latency is an order of magnitude higher prio, than the scheduler latency. above you only talk about scheduler latency. with irq on and nested irqs enabled, the irq latency will have a chance to be less than 2 msec. take audio playback for example, with an huge buffering between userspace and kernel and kernel submitting the next I/O via irqs, the scheduler/userspace latency almost doesn't matter, only the _irq_latency_ matters. hence I don't think not allowing nested irqs at all is a good idea and it's a nice feature to support them. ideally all irq handlers should be quick, but if some is not quick, really it must enable irqs and allow other lowlatency interrupts to be nested on top of it (like audio/video etc..). - 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/