Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760725AbZGINFc (ORCPT ); Thu, 9 Jul 2009 09:05:32 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756453AbZGINFX (ORCPT ); Thu, 9 Jul 2009 09:05:23 -0400 Received: from smtp.nokia.com ([192.100.105.134]:27070 "EHLO mgw-mx09.nokia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756117AbZGINFW (ORCPT ); Thu, 9 Jul 2009 09:05:22 -0400 Message-ID: <4A55EAF9.9070907@nokia.com> Date: Thu, 09 Jul 2009 16:04:57 +0300 From: Artem Bityutskiy Reply-To: Artem.Bityutskiy@nokia.com Organization: Nokia OYJ User-Agent: Thunderbird 2.0.0.21 (X11/20090320) MIME-Version: 1.0 To: Andi Kleen CC: Al Viro , Jens Axboe , "linux-fsdevel@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v3 00/18] periodic write-back timer optimization References: <20090709084822.12122.79749.sendpatchset@localhost.localdomain> <871voq6nh6.fsf@basil.nowhere.org> In-Reply-To: <871voq6nh6.fsf@basil.nowhere.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-OriginalArrivalTime: 09 Jul 2009 13:05:02.0245 (UTC) FILETIME=[DEDA3550:01CA0095] X-Nokia-AV: Clean Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1472 Lines: 36 Andi Kleen wrote: > Artem Bityutskiy writes: > >> The patches attempt to optimize the periodic write-back and stop it when >> there are no dirty data. IOW, we do not want the thread to wake up every >> 5 seconds (by default), find there is nothing to do, and so on. > > Is waking up every 5 seconds really a problem? Yes, it is. In OMAP3 we may switch the core and most of peripherals to off and we may stay in off and consume really few power. And waking up from off every 5 seconds for no good reason is bad. > The normal rule of thumb is iirc that longer sleep times than a few hundred > ms give dimishing returns in terms of power saving. I think our pm guys measured this on OMAP3 and it translates to ~hour of idle mode. And yes, this is bad for devices which run from battery. > A simple way might be simple to batch the timer better with other timers. I agree. There is a lot of work in this direction. There are many places where we could use range hrtimers or deferrable timers and improve PM. But I consider this to be the second level of optimization. The first level is to get rid of unneeded events completely. -- 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/