From owner-freebsd-hackers Wed May 23 18:54:58 2001 Delivered-To: freebsd-hackers@freebsd.org Received: from perninha.conectiva.com.br (perninha.conectiva.com.br [200.250.58.156]) by hub.freebsd.org (Postfix) with ESMTP id 8F83237B423 for ; Wed, 23 May 2001 18:54:50 -0700 (PDT) (envelope-from riel@conectiva.com.br) Received: from burns.conectiva (burns.conectiva [10.0.0.4]) by perninha.conectiva.com.br (Postfix) with SMTP id 1C6F316B63 for ; Wed, 23 May 2001 22:54:47 -0300 (EST) Received: (qmail 8208 invoked by uid 0); 24 May 2001 01:53:14 -0000 Received: from duckman.distro.conectiva (HELO duckman.conectiva.com.br) (root@10.0.17.2) by burns.conectiva with SMTP; 24 May 2001 01:53:14 -0000 Received: from localhost (riel@localhost) by duckman.conectiva.com.br (8.11.3/8.11.3) with ESMTP id f4O1seB28072; Wed, 23 May 2001 22:54:41 -0300 X-Authentication-Warning: duckman.distro.conectiva: riel owned process doing -bs Date: Wed, 23 May 2001 22:54:40 -0300 (BRST) From: Rik van Riel X-X-Sender: To: "Andresen,Jason R." Cc: Kris Kennaway , Nadav Eiron , Subject: Re: technical comparison In-Reply-To: <20010523125626.V87377-100000@nausicaa.mitre.org> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG On Wed, 23 May 2001, Andresen,Jason R. wrote: > On Wed, 23 May 2001, Kris Kennaway wrote: > > That's all well and good, but I thought the aim here was to compare > > Linux and FreeBSD performance on as level playing field as possible? > > You're not measuring FS performance, you're measuring FS performance > > plus cache performance, so your numbers so far tell you nothing > > concrete. *nod* > Yes, they tell us that FreeBSD with softupdates and no write > cache performs better in large cases than Linux with ext2fs and > write caching enabled. > > Also my FreeBSD 4.0 boxes don't have the hw.ata.wc knob, so it's harder > for me to test this. Also, I don't know how ones goes about disabling the > write cache in Linux without recompiling the kernel (which we have some > custom mods in place, so I'm reluctant to do this). 1. I don't think I've ever seen a Linux distro which has write caching enabled by default. Hell, DMA33 isn't even enabled by default ;) 2. hdparm -W0 /dev/ to turn write caching off, -W1 to turn it on 3. I've seen many disks which got _slower_ with write caching turned on. Sure, it helps for sequential IO, but with more random IO the write caching on the disk can interfere really badly with the IO scheduling in the OS ... I've seen as much as a 5x drop in random IO performance with write caching ON compared to OFF. I guess it would be good to follow Kris' suggestions and try to do the tests on a level playing field. The results might just be interesting ;) regards, Rik -- Linux MM bugzilla: http://linux-mm.org/bugzilla.shtml Virtual memory is like a game you can't win; However, without VM there's truly nothing to lose... http://www.surriel.com/ http://www.conectiva.com/ http://distro.conectiva.com/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message