From: Jens Axboe Subject: Re: [PATCH 3/3] block: reimplement FLUSH/FUA to support merge Date: Tue, 25 Jan 2011 12:39:24 +0100 Message-ID: <4D3EB66C.4090006@kernel.dk> References: <1295625598-15203-1-git-send-email-tj@kernel.org> <1295625598-15203-4-git-send-email-tj@kernel.org> <20110121185617.GI12072@redhat.com> <20110123102526.GA23121@htj.dyndns.org> <20110124203155.GA32261@tux1.beaverton.ibm.com> <20110125102128.GO27510@htj.dyndns.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: "Darrick J. Wong" , Vivek Goyal , tytso@mit.edu, shli@kernel.org, neilb@suse.de, adilger.kernel@dilger.ca, jack@suse.cz, snitzer@redhat.com, linux-kernel@vger.kernel.org, kmannth@us.ibm.com, cmm@us.ibm.com, linux-ext4@vger.kernel.org, rwheeler@redhat.com, hch@lst.de, josef@redhat.com To: Tejun Heo Return-path: Received: from 0122700014.0.fullrate.dk ([95.166.99.235]:49327 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751650Ab1AYLjV (ORCPT ); Tue, 25 Jan 2011 06:39:21 -0500 In-Reply-To: <20110125102128.GO27510@htj.dyndns.org> Sender: linux-ext4-owner@vger.kernel.org List-ID: On 2011-01-25 11:21, Tejun Heo wrote: > Hello, Darrick. > > On Mon, Jan 24, 2011 at 12:31:55PM -0800, Darrick J. Wong wrote: >>> So, I think it's better to start with something simple and improve it >>> with actual testing. If the current simple implementation can match >>> Darrick's previous numbers, let's first settle the mechanisms. We can >> >> Yep, the fsync-happy numbers more or less match... at least for 2.6.37: >> http://tinyurl.com/4q2xeao > > Good to hear. Thanks for the detailed testing. > >> I'll give 2.6.38-rc2 a try later, though -rc1 didn't boot for me, so these >> numbers are based on a backport to .37. :( > > Well, there hasn' been any change in the area during the merge window > anyway, so I think testing on 2.6.37 should be fine. > >>> I don't really think we should design the whole thing around broken >>> devices which incorrectly report writeback cache when it need not. >>> The correct place to work around that is during device identification >>> not in the flush logic. >> >> elm3a4_sas and elm3c71_extsas advertise writeback cache yet the >> flush completion times are suspiciously low. I suppose it could be >> useful to disable flushes to squeeze out that last bit of >> performance, though I don't know how one goes about querying the >> disk array to learn if there's a battery behind the cache. I guess >> the current mechanism (admin knob that picks a safe default) is good >> enough. > > Yeap, that or a blacklist of devices which lie. > > Jens, what do you think? If you don't object, let's put this through > linux-next. I like the approach, I'll queue it up for 2.6.39. -- Jens Axboe