Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750944AbXAOQTs (ORCPT ); Mon, 15 Jan 2007 11:19:48 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750943AbXAOQTs (ORCPT ); Mon, 15 Jan 2007 11:19:48 -0500 Received: from e1.ny.us.ibm.com ([32.97.182.141]:41141 "EHLO e1.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750936AbXAOQTr (ORCPT ); Mon, 15 Jan 2007 11:19:47 -0500 Date: Mon, 15 Jan 2007 21:48:10 +0530 From: Srivatsa Vaddagiri To: Oleg Nesterov Cc: Andrew Morton , David Howells , Christoph Hellwig , Ingo Molnar , Linus Torvalds , linux-kernel@vger.kernel.org, Gautham shenoy , "Pallipadi, Venkatesh" Subject: Re: [PATCH] flush_cpu_workqueue: don't flush an empty ->worklist Message-ID: <20070115161810.GB16435@in.ibm.com> Reply-To: vatsa@in.ibm.com References: <20070109050417.GC589@in.ibm.com> <20070108212656.ca77a3ba.akpm@osdl.org> <20070109150755.GB89@tv-sign.ru> <20070109155908.GD22080@in.ibm.com> <20070109163815.GA208@tv-sign.ru> <20070109164604.GA17915@in.ibm.com> <20070109165655.GA215@tv-sign.ru> <20070114235410.GA6165@tv-sign.ru> <20070115043304.GA16435@in.ibm.com> <20070115125401.GA134@tv-sign.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070115125401.GA134@tv-sign.ru> User-Agent: Mutt/1.5.11 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2021 Lines: 51 On Mon, Jan 15, 2007 at 03:54:01PM +0300, Oleg Nesterov wrote: > > - singlethread_cpu needs to be hotplug safe (broken currently) > > Why? Could you explain? What if 'singlethread_cpu' dies? > > - Any reason why cpu_populated_map is not modified on CPU_DEAD? > > Because CPU_DEAD/CPU_UP_CANCELED doesn't wait for cwq->thread to exit. > cpu_populated_map never shrinks, it only grows on CPU_UP_PREPARE. > > We can change this, but it needs some more code, and I am not sure > we need it. Note that a "false" bit in cpu_populated_map only means > that flush_work/flush_workqueue/destroy_workqueu will do lock/unlock > of cwq->lock, nothing more. What abt __create_workqueue/schedule_on_each_cpu? > > - I feel more comfortable if workqueue_cpu_callback were to take > > workqueue_mutex in LOCK_ACQ and release it in LOCK_RELEASE > > notifications. > > The whole purpose of this change to avoid this! I guess it depends on how __create_workqueue/schedule_on_each_cpu is modified (whether we take/release lock upon LOCK_ACQ/LOCK_RELEASE) > > Finally, I wonder if these changes will be unnecessary if we move to > > process freezer based hotplug locking ... > > This change ir not strictly necessary but imho make the code better and > shrinks .text by 379 bytes. > > But I believe that freezer will change nothing for workqueue. We still > need take_over_work(), and hacks like migrate_sequence. And no, CPU_DEAD > can't just thaw cwq->thread which was bound to the dead CPU to complete > kthread_stop(), we should thaw all processes. What abt stopping that thread in CPU_DOWN_PREPARE (before freezing processes)? I understand that it may add to the latency, but compared to the overall latency of process freezer, I suspect it may not be much. -- Regards, vatsa - 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/