From mboxrd@z Thu Jan 1 00:00:00 1970 From: Douglas Gilbert Subject: Re: [PATCH] SCSI sym53c8xx_2: bigger transfer limits Date: Wed, 01 Mar 2006 11:00:56 -0500 Message-ID: <4405C538.4050709@torque.net> References: <20060301152929.GZ4816@suse.de> <1141227541.3276.26.camel@mulgrave.il.steeleye.com> Reply-To: dougg@torque.net Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from canuck.infradead.org ([205.233.218.70]:6584 "EHLO canuck.infradead.org") by vger.kernel.org with ESMTP id S1030218AbWCAQCF (ORCPT ); Wed, 1 Mar 2006 11:02:05 -0500 In-Reply-To: <1141227541.3276.26.camel@mulgrave.il.steeleye.com> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: James Bottomley Cc: Jens Axboe , Kai Makisara , matthew@wil.cx, linux-scsi@vger.kernel.org James Bottomley wrote: > On Wed, 2006-03-01 at 16:29 +0100, Jens Axboe wrote: > >>Strictly speaking, the clustering bit is unrelated. I seem to recall >>Gerard years ago talking about some sym chips that did not like >>clustering, hence it was disabled. > > > Yes, I remember that too ... I've never been able to find out which > chip, though ... the scripts all seem happily coded for variable size sg > segments. > > However, given the new way 2.6 does memory allocations, > ENABLE_CLUSTERING will probably make quite a difference to the size of > the sg list ... since we try to allocate contiguous pages, physical > merging becomes much more of a possibility (I think I last measured it > at around 30% of all SG tables, as opposed to <1% with the old > allocation method). James, So the maximum data carrying size of a scatter gather list is not deterministic? Is the worst case (page_size * SG_ALL)? Doug Gilbert