Re: low(er) disk performance with sched_4bsd then with sched_ule

From: Andrew Gallatin (gallatin_at_cs.duke.edu)
Date: 09/17/05

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    Date: Sat, 17 Sep 2005 17:33:38 -0400 (EDT)
To: joseph.koshy@gmail.com

    Oliver Lehmann writes:
    > Joseph Koshy wrote:
    >
    > > ol> Wow, that update to BETA4 did the trick! While running
    > > ol> SCHED_4BSD:
    > >
    > > Fantastic! What is the profile like with the new 4BSD kernel?
    >
    > http://pofo.de/tmp/gprof.4bsd.3

    I don't know the disk codepath very well, but the samples look a
    little suspect. We're copying a lot of data into and out of the
    kernel, so I would expect the majority of non disk wait time would be
    spent simply copying out the zero-filled pages, and copying them back
    in (AFAIK, dd uses read/write). Where is the time spent in read,
    write, uiomove, bcopy?

    What about ionode allocations, etc? And why do things like
    g_bsd_modify and g_bsd_ioctl rank so high? Aren't those only used
    when dealing with disklabels?

    BTW, I *love* that we've got access to the hw counters, and an easy
    way to do low-overhead profiling of the kernel.

    Drew

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