Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759615AbXFBLtn (ORCPT ); Sat, 2 Jun 2007 07:49:43 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755883AbXFBLta (ORCPT ); Sat, 2 Jun 2007 07:49:30 -0400 Received: from wa-out-1112.google.com ([209.85.146.179]:46966 "EHLO wa-out-1112.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755465AbXFBLt3 (ORCPT ); Sat, 2 Jun 2007 07:49:29 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=beta; h=received:message-id:date:from:user-agent:mime-version:to:cc:subject:references:in-reply-to:x-enigmail-version:content-type:content-transfer-encoding; b=jHjs4w/v5oR4j67Zyn9BtN714avkPSopDSXbQejoea3zZZthaGpQMD+6RmmdE+pFgitMEbWAcywMgUNlUhOkkJKD8MkyORd2FjnM6ucVhe01PuhEcq69z707jDaVogmIM0hGPQYLqwfZDMuLmYFZEejQGB9SfKBDLD38gr2MDUQ= Message-ID: <46613666.7010800@gmail.com> Date: Sat, 02 Jun 2007 18:20:38 +0900 From: Tejun Heo User-Agent: Thunderbird 2.0.0.0 (X11/20070326) MIME-Version: 1.0 To: Jens Axboe CC: David Chinner , david@lang.hm, Phillip Susi , Neil Brown , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, dm-devel@redhat.com, linux-raid@vger.kernel.org, Stefan Bader , Andreas Dilger Subject: Re: [RFD] BIO_RW_BARRIER - what it means for devices, filesystems, and dm/md. References: <465C871F.708@cfl.rr.com> <20070529234832.GT85884050@sgi.com> <20070530061723.GY85884050@sgi.com> <20070531002011.GC85884050@sgi.com> <20070531062644.GI32105@kernel.dk> <20070531070307.GK85884050@sgi.com> <20070531070656.GK32105@kernel.dk> <465F8F71.20302@gmail.com> <20070601082140.GP32105@kernel.dk> In-Reply-To: <20070601082140.GP32105@kernel.dk> X-Enigmail-Version: 0.95.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1282 Lines: 34 Hello, Jens Axboe wrote: >> Would that be very different from issuing barrier and not waiting for >> its completion? For ATA and SCSI, we'll have to flush write back cache >> anyway, so I don't see how we can get performance advantage by >> implementing separate WRITE_ORDERED. I think zero-length barrier >> (haven't looked at the code yet, still recovering from jet lag :-) can >> serve as genuine barrier without the extra write tho. > > As always, it depends :-) > > If you are doing pure flush barriers, then there's no difference. Unless > you only guarantee ordering wrt previously submitted requests, in which > case you can eliminate the post flush. > > If you are doing ordered tags, then just setting the ordered bit is > enough. That is different from the barrier in that we don't need a flush > of FUA bit set. Hmmm... I'm feeling dense. Zero-length barrier also requires only one flush to separate requests before and after it (haven't looked at the code yet, will soon). Can you enlighten me? Thanks. -- tejun - 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/