From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jens Axboe Subject: Re: Warning - running *really* short on DMA buffers while doing file transfers Date: Fri, 27 Sep 2002 08:13:28 +0200 Sender: linux-scsi-owner@vger.kernel.org Message-ID: <20020927061328.GL5646@suse.de> References: <20020925232736.A19209@shookay.newview.com> <20020926061419.GA12862@suse.de> <3D92B17C.9030504@myrealbox.com> <3870780000.1033054272@aslan.scsiguy.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <3870780000.1033054272@aslan.scsiguy.com> List-Id: linux-scsi@vger.kernel.org To: "Justin T. Gibbs" Cc: "Pedro M. Rodrigues" , Mathieu Chouquet-Stringer , linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org On Thu, Sep 26 2002, Justin T. Gibbs wrote: > > I reported this same problem some weeks ago - > > http://marc.theaimsgroup.com/?l=linux-kernel&m=103069116227685&w=2 . > > 2.4.20pre kernels solved the error messages flooding the console, and > > improved things a bit, but system load still got very high and disk read > > and write performance was lousy. Adding more memory and using a > > completely different machine didn't help. What did? Changing the Adaptec > > scsi driver to aic7xxx_old . The performance was up 50% for writes and > > 90% for reads, and the system load was acceptable. And i didn't even had > > to change the RedHat kernel (2.4.18-10) for a custom one. The storage was > > two external Arena raid boxes, btw. > > I would be interested in knowing if reducing the maximum tag depth for > the driver improves things for you. There is a large difference in the > defaults between the two drivers. It has only reacently come to my > attention that the SCSI layer per-transaction overhead is so high that > you can completely starve the kernel of resources if this setting is too > high. For example, a 4GB system installing RedHat 7.3 could not even > complete an install on a 20 drive system with the default of 253 commands. > The latest version of the aic7xxx driver already sent to Marcelo drops the > default to 32. 2.4 layer is most horrible there, 2.5 at least gets rid of the old scsi_dma crap. That said, 253 default depth is a bit over the top, no? -- Jens Axboe, who always uses 4