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    SubjectRe: [patch] softirq performance fixes, cleanups, 2.4.10.

    On Fri, 28 Sep 2001, Andrea Arcangeli wrote:

    > I'm just curious, what are the numbers of your A7 patch compared with
    > this one?

    well, a quick glance shows that this is mostly the -A7 patch with the
    single-loop omitted, right? I tested it before (the unwakeup mechanizm is
    orthogonal to the looping concept), and while unwakeup alone helps
    somewhat, its effect cannot be compared to the effects of looping. Please
    check my previous mail for details, i tried a large set of other
    combinations as well.

    frankly, i dont understand what your problem is with the looping concept.
    It's actually simpler than the mask-bitmap version, and it ensures
    finegrained handling and low latencies of softirq handlers. We loop in the
    softirq handlers themselves already. Ideally we'd like to loop until all
    work is done - but we exit on some limits, and it's generally a good idea
    to not let the handlers themselves loop for a too long time. (to get good
    scheduling latencies.) And we can increase/decrease MAX_SOFTIRQ_RESTART if
    it's ever shown to be excessive/insufficient. (We could even runtime tune
    it - but i thought that to be an overdesigning of a nonexisting problem.)

    (i had an interim version of the patch which had a sysctl-tunable
    MAX_SOFTIRQ_RESTART - this is where the value of '10' comes from. A value
    of '1' means a single-loop. Just to make sure i also tested the 'mask'
    version which is a bit more than just a single loop in the current patch -
    but for tx/rx purposes it's almost equivalent to a single loop.)


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