Date: Wed, 23 May 2001 22:54:40 -0300 (BRST) From: Rik van Riel <riel@conectiva.com.br> To: "Andresen,Jason R." <jandrese@mitre.org> Cc: Kris Kennaway <kris@obsecurity.org>, Nadav Eiron <nadav@cs.Technion.AC.IL>, <hackers@FreeBSD.ORG> Subject: Re: technical comparison Message-ID: <Pine.LNX.4.33.0105232251350.311-100000@duckman.distro.conectiva> In-Reply-To: <20010523125626.V87377-100000@nausicaa.mitre.org>
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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/<drive> 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
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