From mboxrd@z Thu Jan 1 00:00:00 1970 From: Catalin Marinas Subject: Re: [PATCH 1/10] Add generic helpers for arch IPI function calls Date: Tue, 10 Jun 2008 17:53:08 +0100 Message-ID: <1213116788.24701.133.camel@pc1117.cambridge.arm.com> References: <1212051504-12561-1-git-send-email-jens.axboe@oracle.com> <1212051504-12561-2-git-send-email-jens.axboe@oracle.com> <1213109485.24701.107.camel@pc1117.cambridge.arm.com> <20080610154716.GF15481@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: Received: from cam-admin0.cambridge.arm.com ([193.131.176.58]:51977 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753315AbYFJQ7i (ORCPT ); Tue, 10 Jun 2008 12:59:38 -0400 In-Reply-To: <20080610154716.GF15481@linux.vnet.ibm.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: paulmck@linux.vnet.ibm.com Cc: Jens Axboe , linux-kernel@vger.kernel.org, peterz@infradead.org, npiggin@suse.de, linux-arch@vger.kernel.org, jeremy@goop.org, mingo@elte.hu, Russell King On Tue, 2008-06-10 at 08:47 -0700, Paul E. McKenney wrote: > On Tue, Jun 10, 2008 at 03:51:25PM +0100, Catalin Marinas wrote: > > I was thinking whether this condition can be removed and allow the > > smp_call_function*() to be called with IRQs disabled. At a quick look, > > it seems to be possible if the csd_flag_wait() function calls the IPI > > handlers directly when the IRQs are disabled (see the patch below). [...] > There were objections last month: http://lkml.org/lkml/2008/5/3/167 Thanks, I missed this discussion. > The issue was that this permits some interrupts to arrive despite > interrupts being disabled. There seemed to be less resistance to > doing this in the wait==1 case, however. The "(wait == 1) && irqs_disabled()" case is what I would be interested in. In the patch you proposed, this doesn't seem to be allowed (at least from the use of WARN_ON). However, from your post in May: > 5. If you call smp_call_function() with irqs disabled, then you > are guaranteed that no other CPU's smp_call_function() handler > will be invoked while smp_call_function() is executing. this would be possible but no one need this functionality yet. Would one use-case (ARM SMP and DMA cache maintenance) be enough to implement this or I should add it to the ARM-specific code? Thanks. -- Catalin