Date: Mon, 24 Dec 2007 11:10:56 -0500 From: Scott Long <scottl@samsco.org> To: Brett Glass <brett@lariat.net> Cc: stable@freebsd.org Subject: Re: SMP on FreeBSD 6.x and 7.0: Worth doing? Message-ID: <476FDA10.4060107@samsco.org> In-Reply-To: <200712241549.IAA19650@lariat.net> References: <200712220531.WAA09277@lariat.net> <476FBED0.2080400@samsco.org> <200712241549.IAA19650@lariat.net>
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Brett Glass wrote: > At 07:14 AM 12/24/2007, Scott Long wrote: > >> Brett, >> >> There could be several problems here: >> >> 1. WITNESS, INVARIANTS, malloc debugging. Are any of these turned on for you? I don't recall if malloc debugging got turned off yet for the >> 7.0 snapshots. > > I nuked debugging when I recompiled the kernel with SCHED_ULE. Did you also nuke malloc debugging? > >> 2. Disk subsystem. What kind of disk controller are you using? Not all >> drivers work well in FreeBSD. Are linux and freebsd using identical >> hardware? > > They were. The drives are SATA. Connected to what controller? > >> 3. Directory hashing. If you're using squid, you __must__ tune the DIRHASH, otherwise you'll spend a lot of time doing pathname lookups. What filesystem is linux using? > > Whatever comes standard with Ubuntu. Which is??? > As for directory hashing: Squid doesn't > use more than 256 entries in each one, so that's what I normally set. I > also normally do a newfs with parameters that favor the distribution of > object sizes found in Web caches. (We did this on both Linux and FreeBSD.) newfs tuning has little to do with this. > >> Would you mind if I logged into your test system and looked around to >> help diagnose the problem? > > The system isn't online now, because it's been a week since the tests and > I also wanted to try the 6.3 beta and a few hardware changes. > > My guess, based on what I saw, is that UFS2 doesn't take as much advantage of > SMP as Linux's file system does and threads are blocking on file I/O. That's really just speculation on your part, though. UFS is SMP capable, but there really are a whole lot of factors that some into play here so it's really hard to speculate with any chance of success. I can tell you from my experience that a thrashed namei cache looks a lot like slow disk I/O to the casual observer, and that tuning the dirhash is highly important. Thus why I'd like to help out here and see for myself what is going on. Scotthome | help
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