From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:58214) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Sf99O-0002rk-In for qemu-devel@nongnu.org; Thu, 14 Jun 2012 08:27:57 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Sf994-0002lp-CS for qemu-devel@nongnu.org; Thu, 14 Jun 2012 08:27:46 -0400 Received: from mx1.redhat.com ([209.132.183.28]:25425) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Sf994-0002l2-4E for qemu-devel@nongnu.org; Thu, 14 Jun 2012 08:27:26 -0400 Message-ID: <4FD9D8A3.1080005@redhat.com> Date: Thu, 14 Jun 2012 14:27:15 +0200 From: Paolo Bonzini MIME-Version: 1.0 References: <1339582392.24309.15.camel@mengcong> <1339667122.28851.8.camel@mengcong> <20120614120722.GA7128@stefanha-thinkpad.localdomain> In-Reply-To: <20120614120722.GA7128@stefanha-thinkpad.localdomain> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] IO performance test on the tcm-vhost scsi List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Hajnoczi Cc: target-devel@vger.kernel.org, Stefan Hajnoczi , linuxram@us.ibm.com, qemu-devel@nongnu.org, "Nicholas A. Bellinger" , Cong Meng , Anthony Liguori , Asias He Il 14/06/2012 14:07, Stefan Hajnoczi ha scritto: > Perfect, thanks. virtio-scsi userspace is much better than virtio-blk > here. That's unexpected since they both use the QEMU block layer. If > anything, I would have expected virtio-blk to be faster! Yes, I would have expected something similar. A blktrace would be useful here because Asias measured the opposite---virtio-scsi being much slower than virtio-blk. > The second question is why is tcm_vhost faster than virtio-scsi > userspace. I would expect a difference on more high-end benchmarks (i.e. lots of I/O to lots of disks), similar to vhost-blk. In this simple case I wonder how much it is due to the vagaries of the I/O scheduler, or even statistical noise. Paolo