From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id ; Sun, 19 May 2002 16:50:26 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id ; Sun, 19 May 2002 16:50:25 -0400 Received: from krusty.dt.E-Technik.Uni-Dortmund.DE ([129.217.163.1]:25614 "EHLO mail.dt.e-technik.uni-dortmund.de") by vger.kernel.org with ESMTP id ; Sun, 19 May 2002 16:50:24 -0400 Date: Sun, 19 May 2002 22:50:15 +0200 From: Matthias Andree To: linux-kernel@vger.kernel.org Subject: Re: Linux 2.4/2.5 SCSI considerably slower than FreeBSD Message-ID: <20020519205015.GC3008@merlin.emma.line.org> Mail-Followup-To: linux-kernel@vger.kernel.org In-Reply-To: <3CE5D4FC.DB2CC47E@torque.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.3.99i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 18 May 2002, Douglas Gilbert wrote: > $ time sg_dd if=/dev/sg1 of=/dev/null bs=512 count=2m time=1 > time to transfer data was 18.786448 secs, 57.16 MB/sec > 2097152+0 records in > 2097152+0 records out > real 0m18.799s user 0m0.030s sys 0m3.010s In a live system (actually, it's idle, but every 5 s, there is a short burst of disk activity -- reiserfs and ext3fs in use here, something is going on there), sg_dd is not really better than plain dd: > time sg_dd if=/dev/sg0 of=/dev/null count=1310720 > Assume default 'bs' (block size) of 512 bytes > 1310720+0 records in > 1310720+0 records out > > real 0m24.348s gives: 27,56 MB/s. A little better than dd, but still much less than FreeBSD's. > >From memory, dd's performance in the lk 2.4 series was considerably > lower than sg_dd. No doubt FreeBSD would also perform well but I > doubt it could beat linux (2.5) by the type of margin your measurements > indicate. [For sequential reads, tagged queueing will not have a It does. I trust my last figures. I don't trust the above too much because of the bogus 5 s interval write burst. Not sure where it comes from, ext3fs or reiserfs, I'd pretty much like something like an inverse strace: "who is writing to my disk?" > significant impact.] It is also worth noting that the new aic7xxx > and sym53c8xx_2 drivers are essentially the same on Linux and > FreeBSD (i.e. same code base, same maintainers). I know that, and I assume it's not the fault of the drivers themselves (that's because the "far from theoretical optimum" holds on either hardware). Looks like either you're lucky or like Linux has some bad VM interaction or Linux has issues with U160-drives on UWSCSI adapters (yours does U160, ours don't) that FreeBSD doesn't have. (FreeBSD's IDE driver is not as good as the Linux 2.5 IDE driver, so in the end, FreeBSD and Linux are even again ;-) -- Matthias Andree