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    SubjectRe: [RFC] scheduler: improve SMP fairness in CFS
    I'd like to clarify that I'm not trying to push this particular code to 
    the kernel. I'm a researcher. My intent was to point out that we have a
    problem in the scheduler and my dwrr algorithm can potentially help fix
    it. The patch itself was merely a proof-of-concept. I'd be thrilled if the
    algorithm can be proven useful in the real world. I appreciate the people
    who have given me comments. Since then, I've revised my algorithm/code.
    Now it doesn't require global locking but retains strong fairness
    properties (which I was able to prove mathematically).

    Thank you,


    On Thu, 26 Jul 2007, Li, Tong N wrote:

    > On Thu, 2007-07-26 at 23:31 +0200, Ingo Molnar wrote:
    >> * Tong Li <> wrote:
    >>>> you need to measure it over longer periods of time. Its not worth
    >>>> balancing for such a thing in any high-frequency manner. (we'd trash
    >>>> the cache constantly migrating tasks back and forth.)
    >>> I have some data below, but before that, I'd like to say, at the same
    >>> load balancing rate, my proposed approach would allow us to have
    >>> fairness on the order of seconds. I'm less concerned about trashing
    >>> the cache. The important thing is to have a knob that allow users to
    >>> trade off fairness and performance based on their needs. [...]
    >> such a knob already exists to a certain degree, but i havent tested its
    >> full effects on SMP fairness yet. If you pull my scheduler tree:
    >> git://
    >> and if you enable CONFIG_SCHED_DEBUG, then all the sched-domain
    >> parameters become runtime tunable under /proc/sys/cpu*.
    >> Could you try to increase the cross-CPU rebalancing frequency and see
    >> how it impacts the precision of your measurement? Tune 'min_interval'
    >> and 'max_interval' down to increase the frequency of rebalancing.
    >> Ingo
    > Yes, I'll do it when I find time. If anyone is willing to do the
    > testing, please let me know and I can post my benchmark. On the other
    > hand, I don't think tuning the existing knobs will help solve the
    > problem. The root of the problem is that the current load balancing
    > doesn't take into account how much time each task has been running and
    > how much it's entitled. This is why I'm proposing a new approach for
    > solving it. The new approach, as I said, will be much more fair/accurate
    > than the current one even without tuning those balancing intervals
    > (i.e., it's able to provide good fairness even if balancing is less
    > frequent).
    > tong
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