From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47473) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Yhene-0000Xk-Iy for qemu-devel@nongnu.org; Mon, 13 Apr 2015 09:53:19 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Yhenb-00029O-CD for qemu-devel@nongnu.org; Mon, 13 Apr 2015 09:53:18 -0400 Received: from mail-wi0-x22a.google.com ([2a00:1450:400c:c05::22a]:34776) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Yhenb-00029B-4u for qemu-devel@nongnu.org; Mon, 13 Apr 2015 09:53:15 -0400 Received: by widjs5 with SMTP id js5so65143380wid.1 for ; Mon, 13 Apr 2015 06:53:13 -0700 (PDT) Sender: Paolo Bonzini Message-ID: <552BCA46.7010208@redhat.com> Date: Mon, 13 Apr 2015 15:53:10 +0200 From: Paolo Bonzini MIME-Version: 1.0 References: <552834C1.9070105@gmail.com> <20150413014546.GB14218@ad.nay.redhat.com> <552BB682.6070707@gmail.com> In-Reply-To: <552BB682.6070707@gmail.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] Very poor IO performance which looks like some design problem. List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: ein , qemu-devel On 13/04/2015 14:28, ein wrote: > > > Check out my update please: > http://lists.nongnu.org/archive/html/qemu-devel/2015-04/msg01318.html > > Using aio=native,cache=none results in 500%-2000% performance drop > comparing to bare metal and 300%-1000% comparing to > aio=threads,cache=unsafe. Not a surprise that aio=threads,cache=unsafe is faster. With cache=unsafe you're telling QEMU that it's okay to lose data in case of a host power loss. Same for ext2 over XFS (ext2 isn't even journaled!). Thus, use XFS and preallocate storage using the "fallocate" command. Paolo