Date: Fri, 14 Oct 2005 17:46:28 +0100 From: Brian Candler <B.Candler@pobox.com> To: Eric Anderson <anderson@centtech.com> Cc: max@love2party.net, freebsd-current@freebsd.org, "M. Warner Losh" <imp@bsdimp.com> Subject: Re: ufsstat - testers / feedback wanted! Message-ID: <20051014164628.GA20338@uk.tiscali.com> In-Reply-To: <434FDAB2.7040402@centtech.com> References: <200510131412.23525.max@love2party.net> <20051013181026.GB27418@odin.ac.hmc.edu> <20051014091004.GC18513@uk.tiscali.com> <20051014.085816.104604949.imp@bsdimp.com> <434FDAB2.7040402@centtech.com>
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On Fri, Oct 14, 2005 at 11:20:02AM -0500, Eric Anderson wrote: > For statistics gathering purposes though, should I worry about this, or > go for 'fast and imperfect' instead of 'perfect and slow'? With > filesystems, I think it's more important to leave performance high and > get a notion of the statistics, rather than impact performance for > perfect stats (that you may only look at occasionally anyhow). Losing the odd count probably isn't a problem, but I think there's the possibility of a badly wrong value if you're updating a 64-bit word in two halves. For example, it might be possible to wrap around from 00000000ffffffff to 0000000000000000 instead of 0000000100000000.help
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