From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=54737 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1OE0vI-0004r4-Ny for qemu-devel@nongnu.org; Mon, 17 May 2010 10:04:01 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69) (envelope-from ) id 1OE0vH-0006UY-1v for qemu-devel@nongnu.org; Mon, 17 May 2010 10:04:00 -0400 Received: from cantor2.suse.de ([195.135.220.15]:34347 helo=mx2.suse.de) by eggs.gnu.org with esmtp (Exim 4.69) (envelope-from ) id 1OE0vG-0006UG-QY for qemu-devel@nongnu.org; Mon, 17 May 2010 10:03:58 -0400 Message-ID: <4BF14CE9.5040907@suse.de> Date: Mon, 17 May 2010 16:04:25 +0200 From: Alexander Graf MIME-Version: 1.0 References: <1274091292-4812-1-git-send-email-agraf@suse.de> <4BF13D5E.8090006@codemonkey.ws> <8397DB3E-B470-4FBD-903E-8B547631A825@suse.de> <4BF14007.2060603@codemonkey.ws> <095FC499-CB0E-4FB6-902F-0D64A62C8184@suse.de> <4BF1440E.9040209@codemonkey.ws> In-Reply-To: <4BF1440E.9040209@codemonkey.ws> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: [Qemu-devel] Re: [PATCH] Add cache=volatile parameter to -drive List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Anthony Liguori Cc: kwolf@redhat.com, qemu-devel@nongnu.org, hch@lst.de Anthony Liguori wrote: > On 05/17/2010 08:17 AM, Alexander Graf wrote: >> On 17.05.2010, at 15:09, Anthony Liguori wrote: >> >> >>> On 05/17/2010 08:02 AM, Alexander Graf wrote: >>> >>>>> My concern is that ext3 exaggerates the cost of fsync() which will >>>>> result in diminishing value over time for this feature as people >>>>> move to ext4/btrfs. >>>>> >>>>> >>>> There will be ext3 file systems for years out. Just because people >>>> can use better and faster file systems doesn't mean they do. And >>>> I'm sure they can't always choose. If anything, I can try and see >>>> what the numbers look like for xfs. >>>> >>>> >>> But ext3 with barrier=1 is pretty uncommon in practice. Another >>> data point would be an ext3 host file system with barrier=0. >>> >> Who defines what is common and what not? To me, the SLES11 default is >> common. In fact, the numbers in the referred mail were done on an >> 11.1 system. >> > > But it wasn't the SLES10 default so there's a smaller window of > systems that are going to be configured this way. But this is > orthogonal to the main point. Let's quantify how important this > detail is before we discuss the affected user base. Alright. I took my Netbook (2GB of RAM) and a USB hard disk, so I can easily remount the data fs the vmdk image is on. Here are the results: # mkfs.ext3 /dev/sdc1 # mount /dev/sdc1 /mnt -obarrier=1 cache=writeback real 0m52.801s user 0m16.065s sys 0m6.688s cache=volatile real 0m47.876s user 0m15.921s sys 0m6.548s # mount /dev/sdc1 /mnt -obarrier=0 cache=writeback real 0m53.588s user 0m15.901s sys 0m6.576s cache=volatile real 0m48.715s user 0m16.581s sys 0m5.856s I don't see a difference between the results. Apparently the barrier option doesn't change a thing. Alex