Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Thu, 26 Sep 2002 03:07:47 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Thu, 26 Sep 2002 03:07:47 -0400 Received: from packet.digeo.com ([12.110.80.53]:24795 "EHLO packet.digeo.com") by vger.kernel.org with ESMTP id ; Thu, 26 Sep 2002 03:07:31 -0400 Message-ID: <3D92B369.7AFD28D4@digeo.com> Date: Thu, 26 Sep 2002 00:12:41 -0700 From: Andrew Morton X-Mailer: Mozilla 4.79 [en] (X11; U; Linux 2.4.19-rc5 i686) X-Accept-Language: en MIME-Version: 1.0 To: Jens Axboe , Linux Kernel Subject: Re: [PATCH] deadline io scheduler References: <20020925172024.GH15479@suse.de> <3D92A61E.40BFF2D0@digeo.com> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-OriginalArrivalTime: 26 Sep 2002 07:12:42.0136 (UTC) FILETIME=[1ABD1180:01C2652C] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1293 Lines: 55 Andrew Morton wrote: > > I'll test scsi now. > aic7xxx, Fujitsu "MAF3364L SUN36G" (36G SCA-2) Maximum number of TCQ tags=253 fifo_batch time cat kernel/*.c (seconds) 64 58 32 54 16 20 8 58 4 1:15 2 53 Maximum number of TCQ tags=4 fifo_batch time cat kernel/*.c (seconds) 64 53 32 39 16 33 8 21 4 22 2 36 1 22 Maximum number of TCQ tags = 0: fifo_batch time cat kernel/*.c (seconds) 64 22 32 10.3 16 10.5 8 5.5 4 3.2 2 1.9 I selected fifo_batch=16 and altered writes_starved and read_expires again. They made no appreciable difference. >From this I can only conclude that my poor little read was stuck in the disk for ages while TCQ busily allowed new incoming writes to bypass already-sent reads. A dreadful misdesign. Unless we can control this with barriers, and if Fujutsu is typical, TCQ is just uncontrollable. I, for one, would not turn it on in a pink fit. - 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/