From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S938204AbXG0WUq (ORCPT ); Fri, 27 Jul 2007 18:20:46 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S937439AbXG0WUZ (ORCPT ); Fri, 27 Jul 2007 18:20:25 -0400 Received: from neon.samage.net ([85.17.153.66]:46294 "EHLO neon.samage.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S937254AbXG0WUY (ORCPT ); Fri, 27 Jul 2007 18:20:24 -0400 Message-ID: <33456.81.207.0.53.1185574821.squirrel@secure.samage.net> In-Reply-To: <1185573974.2711.8.camel@laptopd505.fenrus.org> References: <200707272243.02336.a1426z@gawab.com> <1185568498.2711.5.camel@laptopd505.fenrus.org> <52449.81.207.0.53.1185573103.squirrel@secure.samage.net> <1185573974.2711.8.camel@laptopd505.fenrus.org> Date: Sat, 28 Jul 2007 00:20:21 +0200 (CEST) Subject: Re: swap-prefetch: A smart way to make good use of idle resources (was: updatedb) From: "Indan Zupancic" To: "Arjan van de Ven" Cc: "Al Boldi" , linux-kernel@vger.kernel.org User-Agent: SquirrelMail/1.4.8 MIME-Version: 1.0 Content-Type: text/plain;charset=UTF-8 Content-Transfer-Encoding: 8bit X-Priority: 3 (Normal) Importance: Normal X-Spam-Score: -1.8 X-Scan-Signature: 71684ae416b12bc74806129cb02de027 Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Sat, July 28, 2007 00:06, Arjan van de Ven wrote: > On Fri, 2007-07-27 at 23:51 +0200, Indan Zupanci >> > also, they take up seek time (5 to 10 msec), so if you were to read >> > something else at the time you get additional latency. >> >> If there's other disk activity swap prefetch shouldn't do much, so this isn't >> really true. > > how do you know there will be other activity? You start the IO and that > basically blacks out the disk for 5 to 10 ms. If the "real" IO gets > submitted in that time you add latency. You cannot predict that IO > happening or not happening. Ah, in that way. Yes, you right about that (though NCQ might help then?), but that's true for all disk activity. Though I think swap prefetch didn't want to run when there was CPU activity, so that would reduce the chance that new IO is submitted right at that moment. I think in practice this isn't worth worrying about, the real issue is the extra disk activity in the first place. Greetings, Indan