Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759410Ab0GVNeg (ORCPT ); Thu, 22 Jul 2010 09:34:36 -0400 Received: from smtp.nokia.com ([192.100.105.134]:50347 "EHLO mgw-mx09.nokia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759370Ab0GVNec (ORCPT ); Thu, 22 Jul 2010 09:34:32 -0400 Subject: Re: [PATCHv2 11/11] writeback: prevent unnecessary bdi threads wakeups From: Artem Bityutskiy Reply-To: dedekind1@gmail.com To: Christoph Hellwig Cc: Dave Chinner , Dave Chinner , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Jens Axboe In-Reply-To: <20100722090023.GA7692@infradead.org> References: <1279704706-1267-1-git-send-email-dedekind1@gmail.com> <1279704706-1267-12-git-send-email-dedekind1@gmail.com> <1279712741.2306.36.camel@localhost> <20100722004155.GZ32635@dastard> <20100722090023.GA7692@infradead.org> Content-Type: text/plain; charset="UTF-8" Date: Thu, 22 Jul 2010 16:27:00 +0300 Message-ID: <1279805220.3044.56.camel@localhost> Mime-Version: 1.0 X-Mailer: Evolution 2.30.2 (2.30.2-1.fc13) Content-Transfer-Encoding: 8bit X-OriginalArrivalTime: 22 Jul 2010 13:33:49.0233 (UTC) FILETIME=[845D2A10:01CB29A2] X-Nokia-AV: Clean Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1467 Lines: 43 On Thu, 2010-07-22 at 05:00 -0400, Christoph Hellwig wrote: > On Thu, Jul 22, 2010 at 10:41:55AM +1000, Dave Chinner wrote: > > if (wakeup_bdi) { > > trace_writeback_wakeup(bdi) > > spin_lock(&bdi->wb_lock); > > if (!bdi->wb.task) {{ > > trace_writeback_wakeup_nothread(bdi); > > wake_up_process(default_backing_dev_info.wb.task); > > } else > > wake_up_process(bdi->wb.task); > > spin_unlock(&bdi->wb_lock); > > That gives us duplicate traces for the first case, what about: > > if (wakeup_bdi) { > spin_lock(&bdi->wb_lock); > if (bdi->wb.task) { > trace_writeback_wake_thread(bdi); > wake_up_process(bdi->wb.task); > } else { > trace_writeback_wake_forker_thread(bdi); > wake_up_process(default_backing_dev_info.wb.task); > } > spin_unlock(&bdi->wb_lock); > } But Dave's version is what we have in 'bdi_queue_work()' as well. I it is OK - first trace point is triggered every time the bdi thread is _wanted_ to be woken up. Then if it does not exist, we need to do something special to wake it up (ask the forker thread which to create it). This is a different event and we use a different trace point. -- Best Regards, Artem Bityutskiy (Артём Битюцкий) -- 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/