From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:38356) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZFjJw-000482-TK for qemu-devel@nongnu.org; Thu, 16 Jul 2015 09:35:29 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZFjJw-0001Hi-3J for qemu-devel@nongnu.org; Thu, 16 Jul 2015 09:35:28 -0400 Date: Thu, 16 Jul 2015 14:35:19 +0100 From: Stefan Hajnoczi Message-ID: <20150716133519.GE16984@stefanha-thinkpad.redhat.com> References: MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="orO6xySwJI16pVnm" Content-Disposition: inline In-Reply-To: Subject: Re: [Qemu-devel] Write requests, during read operations List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Gleb Stepanov Cc: qemu-devel@nongnu.org, qemu-discuss@nongnu.org --orO6xySwJI16pVnm Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Jul 14, 2015 at 05:39:13PM +0300, Gleb Stepanov wrote: > I've measured performance on qcow2 image mounted to nb0 device. nb0 device? > I run tests and > launch iostat -x 1 command to browse I/O operations. Test consists of > sequential read operations with 1 MB size. I've get following output. >=20 > Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s > sda 0.00 5.00 0.00 677.00 0.00 22812.00 > sdb 0.00 0.00 0.00 545.00 0.00 0.00 > dm-0 0.00 0.00 0.00 674.00 0.00 22784.00 > dm-1 0.00 0.00 0.00 7.00 0.00 28.00 > dm-2 0.00 0.00 0.00 0.00 0.00 0.00 > nb0 0.00 0.00 432.00 182.00 55296.00 23296.00 >=20 > So, reading produce a lot of write operations. What is the reason why > these write operations occured? > How to determina block size that qemu operates , because if i've > writtien 55 mb with 1 mb blocks > i should get 55 operations instead of 432. Please post details of the benchmark: * fio job file and fio command-line * commands used to launch QEMU or qemu-nbd --orO6xySwJI16pVnm Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQEcBAEBAgAGBQJVp7MXAAoJEJykq7OBq3PIdlYIAKQgSshTJRSiwF3eD8P/gW1u nNPoe8WNboXAd184lnWbIRajCG7TrLTO1qM1ZaberbwJq7hnK0yFWNujIbBJsdx1 pMNiE5YuYOQYzX0ChuBJJ6RnY+X6P7VPck+zgdWmA+4r3iW7cbuNpO7TNBAQHa27 WzqaeMiq/GMQEcN9fyjzaVuJ/U9i4wabXkstGqeo2bkDhNpKXLujkSDgQgrX5IJT 7uaJ3/EcVU+uH2TV7Tc66YzRyqUzM7rd/MmGwA+vt17HXcZlClneJCzja1s6Wzvc TG7dOmackp/GVwDg3JiIM92oJPu+LXVLz0Ky2OoG3yXBIPeaHghHwgGikksvDLI= =TfkZ -----END PGP SIGNATURE----- --orO6xySwJI16pVnm--