Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Mon, 10 Feb 2003 02:31:38 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Mon, 10 Feb 2003 02:31:38 -0500 Received: from dial-ctb03241.webone.com.au ([210.9.243.241]:35845 "EHLO chimp.local.net") by vger.kernel.org with ESMTP id ; Mon, 10 Feb 2003 02:31:37 -0500 Message-ID: <3E47579A.4000700@cyberone.com.au> Date: Mon, 10 Feb 2003 18:41:14 +1100 From: Nick Piggin User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.1) Gecko/20020913 Debian/1.1-1 MIME-Version: 1.0 To: Andrea Arcangeli CC: Jakob Oestergaard , Andrew Morton , David Lang , riel@conectiva.com.br, ckolivas@yahoo.com.au, linux-kernel@vger.kernel.org, axboe@suse.de Subject: Re: stochastic fair queueing in the elevator [Re: [BENCHMARK] 2.4.20-ck3 / aa / rmap with contest] References:

<20030209203343.06608eb3.akpm@digeo.com> <20030210045107.GD1109@unthought.net> <3E473172.3060407@cyberone.com.au> <20030210073614.GJ31401@dualathlon.random> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1978 Lines: 57 Andrea Arcangeli wrote: >On Mon, Feb 10, 2003 at 03:58:26PM +1100, Nick Piggin wrote: > >>Jakob Oestergaard wrote: >> >> >>>On Sun, Feb 09, 2003 at 08:33:43PM -0800, Andrew Morton wrote: >>> >>> >>>>David Lang wrote: >>>> >>>> >>>>>note that issuing a fsync should change all pending writes to >>>>>'syncronous' >>>>>as should writes to any partition mounted with the sync option, or writes >>>>>to a directory with the S flag set. >>>>> >>>>> >>>>We know, at I/O submission time, whether a write is to be waited upon. >>>>That's in writeback_control.sync_mode. >>>> >>>>That, combined with an assumption that "all reads are synchronous" would >>>>allow the outgoing BIOs to be appropriately tagged. >>>> >>>> >>>This may be a terribly stupid question, if so pls. just tell me :) >>> >>>I assume read-ahead requests go elsewhere? Or do we assume that someone >>>is waiting for them as well? >>> >>>If we assume they are synchronous, that would be rather unfair >>>especially on multi-user systems - and the 90% accuracy that Rik >>>suggested would seem exaggerated to say the least (accuracy would be >>>more like 10% on a good day). >>> >>> >>Remember that readahead gets scaled down quickly if it isn't >>getting hits. It is also likely to be sequential and in the >>track buffer, so it is a small cost. >> >>Huge readahead is a problem however anticipatory scheduling >>will hopefully allow good throughput for multiple read streams >>without requiring much readahead. >> > >the main purpose of readahead is to generate 512k scsi commands when you >read a file with a 4k user buffer, anticipatory scheduling isn't very >related to readahead. > You seem to be forgetting things like seek time. - 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/