Re: user:sys time ratio

From: Poul-Henning Kamp (phk_at_phk.freebsd.dk)
Date: 11/30/03

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    To: Colin Percival <colin.percival@wadham.ox.ac.uk>
Date: Sun, 30 Nov 2003 15:38:54 +0100

    In message <5.0.2.1.1.20031130143248.020dc740@popserver.sfu.ca>, Colin Percival
     writes:
    >At 15:30 30/11/2003 +0100, Poul-Henning Kamp wrote:
    >>In message <5.0.2.1.1.20031130140203.031e8d08@popserver.sfu.ca>, Colin
    >>Percival
    >> writes:
    >> > When running `make buildworld`, I see large amounts of sys time; eg, 27
    >> >minutes user & 14 minutes sys for building 5.2, or 14 minutes user & 10
    >> >minutes sys for building 4.9. I expected the ratio of user:sys to be much
    >> >larger than this, and mailing list traffic indicates that a 4:1 ratio is
    >> >typical.
    > >I've seen UNIX systems have "typical" system/user splits from 1/9 to 9/1
    >>it all depends on what you're doing.
    >
    > Sure, but buildworld is a fairly well-defined benchmark; I wouldn't
    >expect to see such a large difference when running exactly the same code on
    >different systems.

    The amount of system time depends on a lot of environmental factors.

    For instance on my amd64/SMP, the vnode pool is mis-sized, so the the
    namecache does not reflect what is actually already in RAM. The result
    is a fair bit of system time wasted instantiating vnodes from cached
    inode diskblocks. 

    -- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.
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