From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: Re: Warning - running *really* short on DMA buffers while doingfile transfers Date: Fri, 27 Sep 2002 12:07:55 -0700 Sender: linux-kernel-owner@vger.kernel.org Message-ID: <3D94AC8B.4AB6EB09@digeo.com> References: <200209271721.g8RHLTn05231@localhost.localdomain> <2543856224.1033153019@aslan.btc.adaptec.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Return-path: To: "Justin T. Gibbs" Cc: James Bottomley , Jens Axboe , Matthew Jacob , "Pedro M. Rodrigues" , Mathieu Chouquet-Stringer , linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-scsi@vger.kernel.org "Justin T. Gibbs" wrote: > > ... > > The evidence is here: > > > > http://marc.theaimsgroup.com/?l=linux-kernel&m=103302456113997&w=1 > > Which unfortunately characterizes only a single symptom without breaking > it down on a transaction by transaction basis. We need to understand > how many writes were queued by the OS to the drive between each read to > know if the drive is actually allowing writes to pass reads or not. > Given that I measured a two-second read latency with four tags, that would be about 60 megabytes of write traffic after the read was submitted. Say, 120 requests. That's with a tag depth of four. Not sure how old the disk is. It's a 36G Fujitsu SCA-2. Manufactured in 2000, perhaps??