Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751316AbaKYVLG (ORCPT ); Tue, 25 Nov 2014 16:11:06 -0500 Received: from mail-wi0-f180.google.com ([209.85.212.180]:52942 "EHLO mail-wi0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750812AbaKYVLE (ORCPT ); Tue, 25 Nov 2014 16:11:04 -0500 Message-ID: <5474F05E.90401@linaro.org> Date: Tue, 25 Nov 2014 21:10:54 +0000 From: Daniel Thompson User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0 MIME-Version: 1.0 To: Nicolas Pitre , Marc Zyngier CC: Thomas Gleixner , Jason Cooper , Russell King , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "patches@linaro.org" , "linaro-kernel@lists.linaro.org" , John Stultz , Sumit Semwal , Dirk Behme , Daniel Drake , Dmitry Pervushin , Tim Sander Subject: Re: [PATCH 3.18-rc3 v9 1/5] irqchip: gic: Finer grain locking for gic_raise_softirq References: <1415968543-29469-1-git-send-email-daniel.thompson@linaro.org> <1416936401-5147-1-git-send-email-daniel.thompson@linaro.org> <1416936401-5147-2-git-send-email-daniel.thompson@linaro.org> <5474BF19.3040707@arm.com> In-Reply-To: Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 25/11/14 20:17, Nicolas Pitre wrote: > On Tue, 25 Nov 2014, Marc Zyngier wrote: > >> Hi Daniel, >> >> On 25/11/14 17:26, Daniel Thompson wrote: >>> irq_controller_lock is used for multiple purposes within the gic driver. >>> Primarily it is used to make register read-modify-write sequences atomic. >>> It is also used by gic_raise_softirq() in order that the big.LITTLE >>> migration logic can figure out when it is safe to migrate interrupts >>> between physical cores. >>> >>> The second usage of irq_controller_lock is difficult to discern when >>> reviewing the code because the migration itself takes place outside >>> the lock. >>> >>> This patch makes the second usage more explicit by splitting it out into >>> a separate lock and providing better comments. >> >> While we're at it, how about an additional patch that would make this >> lock disappear entirely when the big-little stuff is not compiled in, >> which is likely to be the case on a lot of (dare I say most?) systems? >> That will save expensive barriers that we definitely could do without. > > For the record, I reviewed and ACKed a patch doing exactly that a while > ago: > > http://lkml.org/lkml/2014/8/13/486 Well remembered! That patch had a different motivation but is very similar to mine... so much so I might steal bit of it. I'll make sure I put Stephen on Cc: when I respin with the changes Marc requested. -- 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/