Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Fri, 27 Sep 2002 15:11:24 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Fri, 27 Sep 2002 15:11:24 -0400 Received: from magic.adaptec.com ([208.236.45.80]:64177 "EHLO magic.adaptec.com") by vger.kernel.org with ESMTP id ; Fri, 27 Sep 2002 15:11:22 -0400 Date: Fri, 27 Sep 2002 13:16:16 -0600 From: "Justin T. Gibbs" Reply-To: "Justin T. Gibbs" To: Andrew Morton cc: James Bottomley , Jens Axboe , Matthew Jacob , "Pedro M. Rodrigues" , Mathieu Chouquet-Stringer , linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: Warning - running *really* short on DMA buffers while doingfile transfers Message-ID: <2561606224.1033154176@aslan.btc.adaptec.com> In-Reply-To: <3D94AC8B.4AB6EB09@digeo.com> References: <200209271721.g8RHLTn05231@localhost.localdomain> <2543856224.1033153019@aslan.btc.adaptec.com> <3D94AC8B.4AB6EB09@digeo.com> X-Mailer: Mulberry/3.0.0a4 (Linux/x86) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1339 Lines: 30 >> 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. I still don't follow your reasoning. Your benchmark indicates the latency for several reads (cat kernel/*.c), not the per-read latency. The two are quite different and unless you know the per-read latency and whether it was affected by filling the drive's entire cache with pent up writes (again these are writes that are above and beyond those still assigned tags) you are still speculating that writes are passing reads. If you can tell me exactly how you ran your benchmark, I'll find the information I want by using a SCSI bus analyzer to sniff the traffic on the bus. -- Justin - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/