From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751044AbXAIFE1 (ORCPT ); Tue, 9 Jan 2007 00:04:27 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751046AbXAIFE1 (ORCPT ); Tue, 9 Jan 2007 00:04:27 -0500 Received: from e34.co.us.ibm.com ([32.97.110.152]:34082 "EHLO e34.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751044AbXAIFE0 (ORCPT ); Tue, 9 Jan 2007 00:04:26 -0500 Date: Tue, 9 Jan 2007 10:34:17 +0530 From: Srivatsa Vaddagiri To: Andrew Morton Cc: Oleg Nesterov , David Howells , Christoph Hellwig , Ingo Molnar , Linus Torvalds , linux-kernel@vger.kernel.org, Gautham shenoy Subject: Re: [PATCH] flush_cpu_workqueue: don't flush an empty ->worklist Message-ID: <20070109050417.GC589@in.ibm.com> Reply-To: vatsa@in.ibm.com References: <20070104091850.c1feee76.akpm@osdl.org> <20070106151036.GA951@tv-sign.ru> <20070106154506.GC24274@in.ibm.com> <20070106163035.GA2948@tv-sign.ru> <20070106163851.GA13579@in.ibm.com> <20070106111117.54bb2307.akpm@osdl.org> <20070107110013.GD13579@in.ibm.com> <20070107115957.6080aa08.akpm@osdl.org> <20070107210139.GA2332@tv-sign.ru> <20070108155428.d76f3b73.akpm@osdl.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070108155428.d76f3b73.akpm@osdl.org> User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 08, 2007 at 03:54:28PM -0800, Andrew Morton wrote: > Furthermore I don't know which of these need to be tossed overboard if/when > we get around to using the task freezer for CPU hotplug synchronisation. > Hopefully, a lot of them. I don't really understand why we're continuing > to struggle with the existing approach before that question is settled. Good point! Fundamentally, I think we need to answer this question: "Do we provide *some* mechanism to block concurrent hotplug operations from happening? By hotplug operations I mean both changes to the bitmap and execution of all baclbacks in CPU_DEAD/ONLINE etc" If NO, then IMHO we will be forever fixing races If YES, then what is that mechanism? freeze_processes()? or a magical lock? freeze_processes() cant be that mechanism, if my understanding of it is correct - see http://lkml.org/lkml/2007/1/8/149 and http://marc.theaimsgroup.com/?l=linux-kernel&m=116817460726058. I would be happy to be corrected if the above impression of freeze_processes() is corrected .. -- Regards, vatsa