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    SubjectRe: aim7 scalability issue on 4 socket machine
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    On Fri, 2009-09-18 at 09:12 +0200, Andi Kleen wrote:
    > On Fri, Sep 18, 2009 at 07:53:58AM +0100, Hugh Dickins wrote:
    > > On Thu, 17 Sep 2009, Andrew Morton wrote:
    > > > On Fri, 18 Sep 2009 10:02:19 +0800 "Zhang, Yanmin" <yanmin_zhang@linux.intel.com> wrote:
    > > > > >
    > > > > > So, Yanmin, please retest with http://lkml.org/lkml/2009/9/13/25
    > > > > > and let us know if that works as well for you - thanks.
    > > > > I tested Lee's patch and it does fix the issue.
    > >
    > > Thanks for checking and reporting back, Yanmin.
    > >
    > > >
    > > > Do we think we should cook up something for -stable?
    > >
    > > Gosh, I laughed at Lee (sorry!) for suggesting it for -stable:
    > > is stable really for getting a better number out of a benchmark?
    >
    > When your system is large enough scalability problems (e.g.
    > lock contention) can be a serious bug. i.e. when your workload
    > is 150% slower than expected that can well be a show stopper.
    >
    > Admittedly the workload in this case was a benchmark, but it's
    > not that far fetched to expect the same problem in a real application.
    >
    > We had a similar problem with the accounting lock some time
    > ago, I think that patch also went in.
    >
    > So yes I think simple non intrusive fixes for serious scalability
    > problems should be stable candidates.
    >
    > > > Either this is a regression or the workload is particularly obscure.
    > >
    > > I've not cross-checked descriptions, but assume Lee was actually
    > > testing on exactly the same kind of upcoming Nehalem as Yanmin, and
    > > that machine happens to have characteristics which show up badly here.
    >
    > AFAIK Lee usually tests on large IA64 boxes.

    In this case, it's an x86_64 [DL785] platform--an 8 socket, 4 core
    Shanghai in a glueless, "twisted ladder" config.

    Lee




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