From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S264915AbUEVIm0 (ORCPT ); Sat, 22 May 2004 04:42:26 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S264919AbUEVIm0 (ORCPT ); Sat, 22 May 2004 04:42:26 -0400 Received: from ns.virtualhost.dk ([195.184.98.160]:51147 "EHLO virtualhost.dk") by vger.kernel.org with ESMTP id S264915AbUEVImY (ORCPT ); Sat, 22 May 2004 04:42:24 -0400 Date: Sat, 22 May 2004 10:42:15 +0200 From: Jens Axboe To: Andrew Morton Cc: Chris Mason , linux-kernel@vger.kernel.org Subject: Re: [PATCH] ext3 barrier bits Message-ID: <20040522084214.GS1952@suse.de> References: <20040521093207.GA1952@suse.de> <20040521023807.0de63c7a.akpm@osdl.org> <20040521100234.GK1952@suse.de> <20040521235044.6160cccb.akpm@osdl.org> <20040522073540.GO1952@suse.de> <20040522011139.01a7da10.akpm@osdl.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20040522011139.01a7da10.akpm@osdl.org> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Sat, May 22 2004, Andrew Morton wrote: > > May as well cc lkml on this. It's to do with the disk write barrier > implementation. > > > - How do I know that the barrier code is actually doing stuff? It doesn't > seem to affect benchmarks much, if at all. Usually not a lot of barriers would be generated. If you use reiser and heavy fsync load, it should be pretty apparent of barriers are issued or not (ie compare without barrier + wb cache, with barrier + wb cache, and with/without - wb cache). > - Does reiserfs support `mount -o remount,barrier=flush'? and "=none"? Chris? > - How do I test the "oh, barriers aren't working" fallback code in ext3? A quick hack would be to replace 'err' with '1' in this line in drivers/ide/ide-io.c:void ide_end_drive_cmd(): if (blk_barrier_preflush(rq) || blk_barrier_postflush(rq)) ide_complete_barrier(drive, rq, err); that'll fail the first barrier, should trigger the fall back. Or just try -o barrier=flush on a SCSI drive, should fail the barrier too. > - Does the kernel tell you if your disk doesn't supoprt barriers? ie: > how does the user know if it's working or not? IDE will not tell you, the file system should flag the disabling of barriers (like reiser currently does). Try SCSI case again. -- Jens Axboe