From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935168Ab0COCxP (ORCPT ); Sun, 14 Mar 2010 22:53:15 -0400 Received: from mail2.shareable.org ([80.68.89.115]:47871 "EHLO mail2.shareable.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759579Ab0COCxJ (ORCPT ); Sun, 14 Mar 2010 22:53:09 -0400 Date: Mon, 15 Mar 2010 02:52:49 +0000 From: Jamie Lokier To: Andrew Morton Cc: Thomas Gleixner , LKML , Ingo Molnar , u.kleine-koenig@pengutronix.de, a.p.zijlstra@chello.nl, andrea.gallo@stericsson.com, dbrownell@users.sourceforge.net, eric.y.miao@gmail.com, hugh.dickins@tiscali.co.uk, John Stultz , linux@bohmer.net, nico@marvell.com, Rusty Russell , Greg KH , David Miller Subject: Re: [patch 2/3] genirq: warn about IRQF_SHARED|IRQF_DISABLED at the right place Message-ID: <20100315025249.GP6491@shareable.org> References: <201003112208.o2BM8wJU013575@imap1.linux-foundation.org> <20100312155015.090ba541.akpm@linux-foundation.org> <20100312171423.b7e7a838.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100312171423.b7e7a838.akpm@linux-foundation.org> User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Andrew Morton wrote: > We can tweak and tune until we're blue in the face, but the system's > IRQ latency will always be worse if handlers always run with interrupts > disabled. Are you sure? If good, fast irq handler A runs with interrupts enabled, and good, fast irq handler B runs (interrupting A), A's latency goes _up_ not down. If B happens first, then you get B's latency going up, and A's latency going down. It's not really clear what happens to average latency. But if you know that some handlers require lower latency than others (e.g. serial ports with small FIFOs), it makes sense to prioritise them. -- Jamie