From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Pedro M. Rodrigues" Subject: Re: Warning - running *really* short on DMA buffers while doing file transfers Date: Fri, 27 Sep 2002 14:28:25 +0200 Sender: linux-scsi-owner@vger.kernel.org Message-ID: <3D944EE9.6020702@myrealbox.com> 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; format=flowed Content-Transfer-Encoding: 7bit Return-path: List-Id: linux-scsi@vger.kernel.org To: "Justin T. Gibbs" Cc: Jens Axboe , Mathieu Chouquet-Stringer , linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org 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. > > -- > Justin > > > I have a server available to test it, but the storage in question is already deployed. Yet, by luck (irony apart) i have a maintenance window this weekend for tuning and other matters, i can decrease the maximum number of TCQ commands per device in the proper aic7xxx driver to 32 and report on the results. While trying to solve this problem i browsed RedHat's bugzilla, and there were several people burned with this problem. Hope this sorts it out for them. /Pedro