From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759739AbYEMRQy (ORCPT ); Tue, 13 May 2008 13:16:54 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756334AbYEMRQq (ORCPT ); Tue, 13 May 2008 13:16:46 -0400 Received: from mx28.mail.ru ([194.67.23.67]:3731 "EHLO mx28.mail.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753729AbYEMRQq (ORCPT ); Tue, 13 May 2008 13:16:46 -0400 From: Andrey Borzenkov To: linux-kernel@vger.kernel.org Subject: block device statistics question Date: Tue, 13 May 2008 19:50:10 +0400 User-Agent: KMail/1.9.9 MIME-Version: 1.0 Content-Type: multipart/signed; boundary="nextPart4223084.q4abFq9Mr5"; protocol="application/pgp-signature"; micalg=pgp-sha1 Content-Transfer-Encoding: 7bit Message-Id: <200805131950.16269.arvidjaar@mail.ru> X-Spam: Not detected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --nextPart4223084.q4abFq9Mr5 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Content-Disposition: inline May I ask for clarification of block device stats meaning. I am interested in basically two times - how long IO request has been processed (i.e. from the very beginning it has been submitted till it was finished) as well as how long *device* needed to process request passed to it. /sys/block/XXX/stat provides three set of timings: read ticks, write ticks io_ticks time_in_queue =46rom the description in Documentation/block/stat.txt it is not exactly cl= ear what is counted. read ticks, write ticks =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D These values count the number of milliseconds that I/O requests have waited on this block device.=20 Q. Waited since which point? From the point request entered block subsystem or from the point request has been submitted to physical device (well, not necessarily really physical of course) io_ticks =3D=3D=3D=3D=3D=3D=3D=3D This value counts the number of milliseconds during which the device has had I/O requests queued. Q. "queued" - means "waited for submission"? I.e. this time does not include actual IO processing by device? Or "queued" - submitted to device? time_in_queue =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D This value counts the number of milliseconds that I/O requests have waited on this block device. Q. What is the difference between this one and read/write ticks? It really sounds like time_in_queue =3D=3D read ticks + write ticks? In this case wha= t is the point in making it separate? TIA =2Dandrey --nextPart4223084.q4abFq9Mr5 Content-Type: application/pgp-signature; name=signature.asc Content-Description: This is a digitally signed message part. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) iEYEABECAAYFAkgpuLQACgkQR6LMutpd94wg6QCgrrkh7b+lo4cAkdCwXkYb7kll 4yEAnjfsElLXUhb/BlLVIrp+Fdqw4fII =CJwl -----END PGP SIGNATURE----- --nextPart4223084.q4abFq9Mr5--