Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753064AbZK3Uju (ORCPT ); Mon, 30 Nov 2009 15:39:50 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752062AbZK3Ujt (ORCPT ); Mon, 30 Nov 2009 15:39:49 -0500 Received: from mail2.shareable.org ([80.68.89.115]:58483 "EHLO mail2.shareable.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751333AbZK3Ujs (ORCPT ); Mon, 30 Nov 2009 15:39:48 -0500 Date: Mon, 30 Nov 2009 20:39:33 +0000 From: Jamie Lokier To: Russell King - ARM Linux Cc: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?= , David Brownell , Eric Miao , Peter Zijlstra , John Stultz , Rusty Russell , LKML , Ingo Molnar , Thomas Gleixner , Nicolas Pitre , Andrew Morton , linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] warn about shared irqs requesting IRQF_DISABLED registered with setup_irq Message-ID: <20091130203933.GC5560@shareable.org> References: <20091127195857.GB28193@n2100.arm.linux.org.uk> <1259356206-14843-1-git-send-email-u.kleine-koenig@pengutronix.de> <20091128200344.GA1272@pengutronix.de> <20091129023118.GA21529@shareable.org> <20091129102635.GA22653@pengutronix.de> <20091129151840.GA30813@shareable.org> <20091129152757.GF11445@n2100.arm.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20091129152757.GF11445@n2100.arm.linux.org.uk> 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 Content-Length: 1260 Lines: 27 Russell King - ARM Linux wrote: > On Sun, Nov 29, 2009 at 03:18:40PM +0000, Jamie Lokier wrote: > > Or we could do away with this silliness and just switch everything to > > threaded interrupts with RT-priorities ;-) > > ... thereby needlessly increasing the latency of all interrupt handling > and probably breaking some devices. It's not that cut and dried. RT gives you priorities where you might not have had them before, so in some cases can reduce worst-case latency for critical devices. IRQF_DISABLED is a cheap two-level priority scheme; RT threaded interrupts extend it. The extra processing increases latency, yes, but that is in a sense a scheduling fast-path problem; it's not _intrinsic_ to threaded interrupts that they have to have higher latency (you don't have to use the normal calculation or task switch to get equivalent behaviour), but undoubtedly trying to optimise that leads to very twisty code and state representations, and I don't see it happening in Linux any time soon. -- Jamie -- 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/