From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261993AbULHBkL (ORCPT ); Tue, 7 Dec 2004 20:40:11 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261975AbULHBkK (ORCPT ); Tue, 7 Dec 2004 20:40:10 -0500 Received: from mail-relay-3.tiscali.it ([213.205.33.43]:39322 "EHLO mail-relay-3.tiscali.it") by vger.kernel.org with ESMTP id S261993AbULHBhh (ORCPT ); Tue, 7 Dec 2004 20:37:37 -0500 Date: Wed, 8 Dec 2004 02:37:32 +0100 From: Andrea Arcangeli To: Nick Piggin Cc: Jens Axboe , Andrew Morton , linux-kernel@vger.kernel.org Subject: Re: Time sliced CFQ io scheduler Message-ID: <20041208013732.GF16322@dualathlon.random> References: <20041202130457.GC10458@suse.de> <20041202134801.GE10458@suse.de> <20041202114836.6b2e8d3f.akpm@osdl.org> <20041202195232.GA26695@suse.de> <20041208003736.GD16322@dualathlon.random> <1102467253.8095.10.camel@npiggin-nld.site> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1102467253.8095.10.camel@npiggin-nld.site> X-GPG-Key: 1024D/68B9CB43 13D9 8355 295F 4823 7C49 C012 DFA1 686E 68B9 CB43 X-PGP-Key: 1024R/CB4660B9 CC A0 71 81 F4 A0 63 AC C0 4B 81 1D 8C 15 C8 E5 User-Agent: Mutt/1.5.6i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Dec 08, 2004 at 11:54:13AM +1100, Nick Piggin wrote: > That is synch write bandwidth. Yes that seems to be a problem. It's not just sync write, it's a write in general, blkdev doesn't know if the one waiting is pdflush or some other task. Once this will be fixed I will have to reconsider my opinion of course, but I guess after it gets fixed the benefit of "as" on the desktop will as well decrease compared to cfq. The desktop is ok with "as" simply because it's normally optimal to stop writes completely, since there are few apps doing write journaling or heavy writes, and there's normally no contigous read happening in the background. Desktop just needs a temporary peak read max bandwidth when you click on openoffice or similar app (and "as" provides it). But on a mixed server doing some significant read and write (i.e. somebody downloading the kernel from kernel.org and installing it on some application server) I don't think "as" is general purpose enough. Another example is the multiuser usage with one user reading a big mbox folder in mutt, whole the other user s exiting mutt at the same time. The one exiting will pratically have to wait the first user to finish its read I/O. All I/O becomes sync when it exceeds the max size of the writeback cache. "as" is clearly the best for the common case of the very desktop usage (i.e. machine 99.9% idle and without any I/O except when starting an app or saving a file, and the user noticing delay only while waiting the window to open up after he clicked the button). But I believe cfq is better for a general purpose usage where we cannot assume how the kernel will be used.