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    SubjectRe: 20% performance drop on PostgreSQL 9.2 from kernel 3.5.3 to 3.6-rc5 on AMD chipsets - bisected
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    On Sat, 2012-09-15 at 19:08 +0200, richard -rw- weinberger wrote: 
    > On Sat, Sep 15, 2012 at 6:36 PM, Mike Galbraith <efault@gmx.de> wrote:
    > >> Just using futex is unfortunately not the answer either.
    > >
    > > Yes, postgress performs loads better with it's spinlocks, but due to
    > > that, it necessarily _hates_ preemption. How the is the scheduler
    > > supposed to know that any specific userland task _really_ shouldn't be
    > > preempted at any specific time, else bad things follow?
    >
    > Why perform custom userspace spinlocks better than futex() based ones?
    > I thought we have futex() to get rid of the custom ones...
    > Makes futex() only sense when things like priority inheritance are needed?

    Dunno. Likely because data doesn't go cold when you spin a bit, but go
    to sleep and the next guy may stomp cache flat with size XXL boots.

    -Mike



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