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    SubjectRe: [this_cpu_xx V5 19/19] SLUB: Experimental new fastpath w/o interrupt disable
    * Christoph Lameter ( wrote:
    > On Wed, 7 Oct 2009, Mathieu Desnoyers wrote:
    > > Usually, when preemption is disabled, the scheduler restrain from
    > > executing. *Now the important point*: the criterion that bounds the
    > > maximum amount of time before the scheduler will re-check for pending
    > > preemption is when preempt_enable() will re-activate preemption.
    > Which creates additional overhead in the allocator.

    Which we like to keep as low as possible, I agree.

    > > But because you run preempt_enable with interrupts off, the scheduler
    > > check is not done. And it's not done when interrupts are re-activated
    > > neither.
    > Ok so we should be moving the preempt_enable after the irq enable. Then we
    > will call into the scheduler at the end of the slow path. This may add
    > significantly more overhead that we had before when we simply disabled
    > and enabled interrupts...

    You are already calling the scheduler when ending the _fast_ path. I
    don't see the problem with calling it when you end the slow path


    Mathieu Desnoyers
    OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68

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