From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jens Axboe Subject: Re: Max IO size Date: Fri, 2 Aug 2002 08:44:03 +0200 Sender: linux-scsi-owner@vger.kernel.org Message-ID: <20020802064403.GG1512@suse.de> References: <20020801084547.GA12715@suse.de> <20020801235432.14372.qmail@web14005.mail.yahoo.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20020801235432.14372.qmail@web14005.mail.yahoo.com> List-Id: linux-scsi@vger.kernel.org To: Mukul Kotwani Cc: linux-scsi@vger.kernel.org On Thu, Aug 01 2002, Mukul Kotwani wrote: > > Thanks for the reply! > > All my values are set high. The sg_tablesize value is > set to 249, max_sectors set to 1024, and I dont think > there is any other value which affects IO size as > such. I didnt see anything called max segment size/max > size in the host template. Any other things I am > missing? The max segment size is a property of the queue associated with the SCSI devices, it's in fact not directly controllable by the low level driver in the 2.4 kernels. What you can set in this regard is 'use_clustering'. With that set, the mid layer will attempt to merge contigious pages into the same scatter gather segment. This usually only provides a benefit with 1kb transfers (since they will typically be submitted in multiples anyway from the same page, thus it's easy to cluster them), with eg 4kb transfer sizes the amount of clustering that will happen is neglible. -- Jens Axboe