From mboxrd@z Thu Jan 1 00:00:00 1970 From: Doug Ledford Subject: Re: Degraded I/O performance, since 2.5.41 Date: Thu, 10 Oct 2002 21:59:33 -0400 Sender: linux-scsi-owner@vger.kernel.org Message-ID: <20021011015933.GC27073@redhat.com> References: <3DA611DF.3000206@us.ibm.com> <200210110109.g9B19FJ14530@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <200210110109.g9B19FJ14530@localhost.localdomain> List-Id: linux-scsi@vger.kernel.org To: James Bottomley Cc: Dave Hansen , linux-scsi@vger.kernel.org On Thu, Oct 10, 2002 at 06:09:14PM -0700, James Bottomley wrote: > OK, this patch should fix it. Do your performance numbers for ips improve > again with this? Well, it should help. Most drivers set cmd_per_lun too low to really be good here (and well they should because you only want it big enough to keep a CD-R or tape streaming, no more, because it's only intended to be used on non-tagged devices, disks should have their depth set via scsi_adjust_queue_depth() by the low level driver). This is in fact the right thing to do though, so I've added it to my code here as well since it's required in order for cmd_per_lun to do the right thing in regards to untagged devices. The real answer is to update the ServeRAID driver to the new tagged queue adjustment mechanism I just wrote an intro to and sent to linux-scsi. As a side note, the generic block layer tagged queueing mechanism may not be suitable for a lot of SCSI drivers (I know it's not suitable for mine at all). How many of the drivers in the scsi tree today keep a shared tag table between all devices on a host and how many of them have separate tag tables for each device? Show of hands anyone? Justin, what about the modern aic7xxx driver? Gerard? > James > -- Doug Ledford 919-754-3700 x44233 Red Hat, Inc. 1801 Varsity Dr. Raleigh, NC 27606