From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Bottomley Subject: Re: [Bug 41552] Performance of writing and reading from multiple drives decreases by 40% when going from Linux Kernel 2.6.36.4 to 2.6.37 (and beyond) Date: Tue, 23 Aug 2011 09:00:57 -0500 Message-ID: <1314108057.13645.8.camel@mulgrave> References: <201108222107.p7ML767K019660@demeter2.kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: Received: from bedivere.hansenpartnership.com ([66.63.167.143]:35389 "EHLO bedivere.hansenpartnership.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751346Ab1HWOBB (ORCPT ); Tue, 23 Aug 2011 10:01:01 -0400 In-Reply-To: <201108222107.p7ML767K019660@demeter2.kernel.org> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: bugzilla-daemon@bugzilla.kernel.org Cc: linux-scsi@vger.kernel.org On Mon, 2011-08-22 at 21:07 +0000, bugzilla-daemon@bugzilla.kernel.org wrote: > We were using the default CFQ scheduler. I will change it to deadline and see > what happens. Also, we are not using a file system to perform the writes, > rather we are sending SCSI commands directly to the devices, nor are we doing > anything special to the disks with a device mapper. We simply write to each > one on a different thread one sector at a time. > > I will attempt to get the trace and will add it if I can. If you're just using a SG_IO type scsi command, then virtually nothing we've done in block/scsi should affect this; certainly not the elevators since we don't do merging on SG_IO, we just use them for queueing. Since you say "write to each one on a different thread", it's possible that some scheduler change may have impacted this. James