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    SubjectRe: [RFC PATCH 3/3 -v2] x86,smp: auto tune spinlock backoff delay factor
    >>> On 27.12.12 at 20:09, Rik van Riel <riel@redhat.com> wrote:
    > On 12/27/2012 01:41 PM, Jan Beulich wrote:
    >>>>> Rik van Riel <riel@redhat.com> 12/27/12 4:01 PM >>>
    >>> On 12/27/2012 09:27 AM, Eric Dumazet wrote:
    >>>> So the hash sounds good to me, because the hash key could mix both lock
    >>>> address and caller IP ( __builtin_return_address(1) in
    >>>> ticket_spin_lock_wait())
    >>>
    >>> The lock acquisition time depends on the holder of the lock,
    >>> and what the CPUs ahead of us in line will do with the lock,
    >>> not on the caller IP of the spinner.
    >>
    >> The lock holder could supply its __builtin_return_address(0) for use
    >> in eventual hashing.
    >>
    >> Also, with all of this - did you evaluate the alternative of using
    >> monitor/mwait instead?
    >
    > How much bus traffic do monitor/mwait cause behind the scenes?

    I would suppose that this just snoops the bus for writes, but the
    amount of bus traffic involved in this isn't explicitly documented.

    One downside of course is that unless a spin lock is made occupy
    exactly a cache line, false wakeups are possible.

    Jan



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