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    SubjectRe: [PATCH 1/1] linux headers: header file(s) changes to enable spinlock use jumplabel
    On 02/20/2012 03:03 PM, Gleb Natapov wrote:
    > On Mon, Feb 20, 2012 at 11:44:25AM +0530, Raghavendra K T wrote:
    >> On 02/20/2012 10:46 AM, Jeremy Fitzhardinge wrote:
    >> But does pvlock have to use jump
    >>>> label? I looked at the code and it is used like paravirt patching. Meaning
    >>>> it is patched only once on a boot up when XEN is detected. May be use
    >>>> paravirt patching instead of jump label? What if jump label will want
    >>>> to use spinlock for some reason in the future (it uses mutex currently)?
    >>> The point of the pv ticketlocks is to avoid any pvop calls on the
    >>> lock/unlock fastpath, relegating them to only the slow path.
    >>> Unfortunately, the pv unlock case can't be identical with the non-pv
    >>> unlock, and jump_labels are lighter weight and more efficient than pvops.
    >>> It doesn't matter if jump_labels start using spinlocks; all we need the
    >>> jump_label machinery to do is patch the jump sites in the code so that
    >>> one of two execution paths can be selected. Since all the ticketlock
    >>> jump_label patching happens before SMP is enabled, there's no problem
    >>> with changing a lock while a cpu is executing the code.
    >> I also felt agreeing with Jeremy. seemed to me that latter is more
    >> performance friendly. no?.
    > I thought not about pvop, but about alternative(). jump_labels is used
    > by spinlock to patch out jump into nops It can be done via alternative()
    > too I think.

    I had remembered that this discussion already happened with Jeremy's V5
    of ticketlock patches. pulling out link :

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