Date: Fri, 14 Oct 2005 12:40:49 -0500 From: Eric Anderson <anderson@centtech.com> To: Brian Candler <B.Candler@pobox.com> Cc: max@love2party.net, freebsd-current@freebsd.org, "M. Warner Losh" <imp@bsdimp.com> Subject: Re: ufsstat - testers / feedback wanted! Message-ID: <434FEDA1.4060803@centtech.com> In-Reply-To: <20051014164628.GA20338@uk.tiscali.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> <20051014164628.GA20338@uk.tiscali.com>
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Brian Candler wrote: > 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. I suppose one could argue that this problem is no worse than using 32bit integers, except it would be right more often than not. (right?) Eric -- ------------------------------------------------------------------------ Eric Anderson Sr. Systems Administrator Centaur Technology Anything that works is better than anything that doesn't. ------------------------------------------------------------------------
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