From mboxrd@z Thu Jan 1 00:00:00 1970 From: Doug Ledford Subject: Re: [patch 2.5] ips queue depths Date: Tue, 15 Oct 2002 16:52:18 -0400 Sender: linux-scsi-owner@vger.kernel.org Message-ID: <20021015205218.GG4391@redhat.com> References: <20021015194705.GD4391@redhat.com> <20021015130445.A829@eng2.beaverton.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20021015130445.A829@eng2.beaverton.ibm.com> List-Id: linux-scsi@vger.kernel.org To: "Jeffery, David" , 'Dave Hansen' , "'linux-scsi@vger.kernel.org'" On Tue, Oct 15, 2002 at 01:04:45PM -0700, Patrick Mansfield wrote: > > I totally agree the queue depth should not be limited based on the number of > devices, but there should be a maximum limit - as Justin noted with the > aic driver, using a large default queue depth (he had 253 or so) is not > good with linux. That's largely due to the scsi_request_fn() in its current form. > The queue depth should be as small as possible without limiting the > performance. Which happens to be a magic number that no one really knows I think ;-) Current goals of the work I'm doing include making this adjustable so you aren't wasting queue depth on devices that have a hard limit less than your initial queue depth value and changing the scsi_request_fn() to be more fair with command allocation on a controller in the presence of starvation (and of course, starvation is only possible when the queue depth of all devices is greater than the depth of the controller, so obviously the starvation code in scsi_request_fn() is something controllers have been avoiding by limiting queue depths on individual devices). The adjustable queue depth work has been mostly done and sent to linus. I'm trying to finish up the last few controllers that haven't been modified to the new scheme yet. The request_fn work is on hold until this is done (because the breakage made everyone moan so loadly that I dropped everything else until this is taken care of). -- Doug Ledford 919-754-3700 x44233 Red Hat, Inc. 1801 Varsity Dr. Raleigh, NC 27606