Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752826AbXFDHkP (ORCPT ); Mon, 4 Jun 2007 03:40:15 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752171AbXFDHkB (ORCPT ); Mon, 4 Jun 2007 03:40:01 -0400 Received: from wa-out-1112.google.com ([209.85.146.180]:64626 "EHLO wa-out-1112.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752086AbXFDHj7 (ORCPT ); Mon, 4 Jun 2007 03:39:59 -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=GKNwlZHF4CrH5ulNmiYq8qBMTAfFGxyEUPpQwZL+uvIEmo+QJYG+JMdbjB4olsXgbSFYBhnRwzwpy6APeGpgHVQ1+Ek2Q7FkF+u+kYy0d8mPC6CeZeTLCpGDsZGGmMqqdvwe9tUCWiGRhFXDLeKBiDJ+3nbwKKQamB80NFkP3Zc= Message-ID: <4663C1C1.5000009@gmail.com> Date: Mon, 04 Jun 2007 16:39:45 +0900 From: Tejun Heo User-Agent: Icedove 1.5.0.10 (X11/20070307) 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: <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> <46613666.7010800@gmail.com> <20070602143438.GB32105@kernel.dk> In-Reply-To: <20070602143438.GB32105@kernel.dk> X-Enigmail-Version: 0.94.2.0 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: 1652 Lines: 37 Jens Axboe wrote: > On Sat, Jun 02 2007, Tejun Heo wrote: >> 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? > > Yeah, that's what the zero-length barrier implementation I posted does. > Not sure if you have a question beyond that, if so fire away :-) I thought you were talking about adding BIO_RW_ORDERED instead of exposing zero length BIO_RW_BARRIER. Sorry about the confusion. :-) -- 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/