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    SubjectRe: [rfc] balance-on-fork NUMA placement
    On Thu, Aug 02, 2007 at 11:33:39AM -0700, Martin Bligh wrote:
    > Nick Piggin wrote:
    > >On Wed, Aug 01, 2007 at 03:52:11PM -0700, Martin Bligh wrote:
    > >>>And so forth. Initial forks will balance. If the children refuse to
    > >>>die, forks will continue to balance. If the parent starts seeing short
    > >>>lived children, fork()s will eventually start to stay local.
    > >>Fork without exec is much more rare than without. Optimising for
    > >>the uncommon case is the Wrong Thing to Do (tm). What we decided
    > >
    > >It's only the wrong thing to do if it hurts the common case too
    > >much. Considering we _already_ balance on exec, then adding another
    > >balance on fork is not going to introduce some order of magnitude
    > >problem -- at worst it would be 2x but it really isn't too slow
    > >anyway (at least nobody complained when we added it).
    > >
    > >One place where we found it helps is clone for threads.
    > >
    > >If we didn't do such a bad job at keeping tasks together with their
    > >local memory, then we might indeed reduce some of the balance-on-crap
    > >and increase the aggressiveness of periodic balancing.
    > >
    > >Considering we _already_ balance on fork/clone, I don't know what
    > >your argument is against this patch is? Doing the balance earlier
    > >and allocating more stuff on the local node is surely not a bad
    > >idea.
    >
    > I don't know who turned that on ;-( I suspect nobody bothered
    > actually measuring it at the time though, or used some crap
    > benchmark like stream to do so. It should get reverted.

    So you have numbers to show it hurts? I tested some things where it
    is not supposed to help, and it didn't make any difference. Nobody
    else noticed either.

    If the cost of doing the double balance is _really_ that painful,
    then we ccould skip balance-on-exec for domains with balance-on-fork
    set.
    -
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