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    SubjectRe: [patch 0/3] j_state_lock, j_list_lock, remove-bitlocks

    * Steven Rostedt <> wrote:

    > > > ooh, I'd rather not. I spent an intense three days removing all the
    > > > sleeping locks from ext3 (and three months debugging the result).
    > > > Ended up gaining 1000% on 16-way.
    > > >
    > > > Putting them back in will really hurt the SMP performance.
    > >
    > > ah. Yeah. Sniff.
    > >
    > > if we gain 1000% on a 16-way then there's something really wrong about
    > > semaphores (or scheduling) though. A semaphore is almost a spinlock, in
    > > the uncontended case - and even under contention we really (should) just
    > > spend the cycles that we'd spend spinning. There will be some
    > > intermediate contention level where semaphores hurt, but 1000% sounds
    > > truly excessive.
    > >
    > Could it possibly be that in the process of removing all the sleeping
    > locks from ext3, that Andrew also removed a flaw in ext3 itself that
    > is responsible for the 1000% improvement?

    i think the chances for that are really remote. I think it must have
    been a workload ending up scheduling itself to death, while spinlocks
    force atomicity of execution and affinity.

    we should be able to see the same scenario with PREEMPT_RT on a 16-way

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