From mboxrd@z Thu Jan 1 00:00:00 1970 From: Artem Bityutskiy Subject: Re: [PATCH v3 00/18] periodic write-back timer optimization Date: Thu, 09 Jul 2009 16:04:57 +0300 Message-ID: <4A55EAF9.9070907@nokia.com> References: <20090709084822.12122.79749.sendpatchset@localhost.localdomain> <871voq6nh6.fsf@basil.nowhere.org> Reply-To: Artem.Bityutskiy@nokia.com Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Al Viro , Jens Axboe , "linux-fsdevel@vger.kernel.org" , "linux-kernel@vger.kernel.org" To: Andi Kleen Return-path: 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 In-Reply-To: <871voq6nh6.fsf@basil.nowhere.org> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: Andi Kleen wrote: > Artem Bityutskiy writes: >=20 >> 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 e= very >> 5 seconds (by default), find there is nothing to do, and so on. >=20 > 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 h= undred > 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 tim= ers. 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. --=20 Best Regards, Artem Bityutskiy (=D0=90=D1=80=D1=82=D1=91=D0=BC =D0=91=D0=B8=D1=82=D1=8E= =D1=86=D0=BA=D0=B8=D0=B9) -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel= " in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html