Re: I/O or Threading Suffer

From: Robert Watson (rwatson_at_FreeBSD.ORG)
Date: 07/20/04

  • Next message: Scott Long: "Re: HEADS UP [Re: thread+preemption stability improvement]" 
    Date: Tue, 20 Jul 2004 12:39:04 -0400 (EDT)
To: Mark Murray <mark@grondar.org>

    On Tue, 20 Jul 2004, Mark Murray wrote:

    > Robert Watson writes:
    > > Mark -- how much
    > > computation is being done here -- would it be worth dropping the Giant
    > > lock during that computation so that the thread can yield without
    > > generating a priority inversion?
    >
    > I'm sure it could. There are some Giant issues related to the UIO stuff
    > that bit me in the bum when I removed the NEEDS_GIANT flag from the
    > device, but I'm reasonably sure that with careful work this can be
    > untangled.

    UIO shouldn't require Giant. Are you sure it still does? FYI, I'm not
    even thinking you have to mark the whole device driver as not requiring
    Giant, just dropping Giant about some of the long running work (and maybe
    conditional on the amount of work). For a small random read, it's not
    worth it, but for sustained large reads of randomness, it might be
    interesting to see what impact it has. We could even consider a yield of
    some sort.

    Anyhow, up front, it might be sufficient to drop and reacquire giant and
    see what impact it has for the test scenario we're currently looking at.

    Robert N M Watson FreeBSD Core Team, TrustedBSD Projects
    robert@fledge.watson.org Principal Research Scientist, McAfee Research

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  • Next message: Scott Long: "Re: HEADS UP [Re: thread+preemption stability improvement]"

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