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    SubjectRe: [PATCH] 2.6.0 batch scheduling, HT aware

    Con Kolivas wrote:

    >I've done a resync and update of my batch scheduling that is also hyper-thread
    >What is batch scheduling? Specifying a task as batch allows it to only use cpu
    >time if there is idle time available, rather than having a proportion of the
    >cpu time based on niceness.
    >Why do I need hyper-thread aware batch scheduling?
    >If you have a hyperthread (P4HT) processor and run it as two logical cpus you
    >can have a very low priority task running that can consume 50% of your
    >physical cpu's capacity no matter how high priority tasks you are running.
    >For example if you use the distributed computing client setiathome you will
    >be effectively be running at half your cpu's speed even if you run setiathome
    >at nice 20. Batch scheduling for normal cpus allows only idle time to be used
    >for batch tasks, and for HT cpus only allows idle time when both logical cpus
    >are idle.
    >This is not being pushed for mainline kernel inclusion, but the issue of how
    >to prevent low priority tasks slowing down HT cpus needs to be considered for
    >the mainline HT scheduler if it ever gets included. This patch provides a
    >temporising measure for those with HT processors, and a demonstrative way to
    >handle them in mainline.

    I wonder how does Intel suggest we handle this problem? Batch scheduling
    aside, I wonder how to do any sort of priorities at all? I think POWER5
    can do priorities in hardware, that is the only sane way I can think of
    doing it.

    I think this patch is much too ugly to get into such an elegant scheduler.
    No fault to you Con because its an ugly problem.

    How about this: if a task is "delta" priority points below a task running
    on another sibling, move it to that sibling (so priorities via timeslice
    start working). I call it active unbalancing! I might be able to make it
    fit if there is interest. Other suggestions?

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