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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
    On Fri, Sep 14, 2012 at 2:56 PM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
    >
    > Both things change semantics, not looking at the entire package is new
    > too.

    Well, the "idle_buddy" thing on its own could be considered to be
    purely a caching thing.

    Sure, it doesn't take tsk_cpus_allowed() into account while setting up
    the cache (since it's not dynamic enough), but *assuming* the common
    case is that people let threads be on any of the cores of a package,
    it should be possible to make the cache 100% equivalent with no
    semantic change. No?

    The code doesn't even try to do that kind of "don't change semantics",
    though, and makes the idle-buddy thing entirely different.

    Linus


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