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


On Wed, 16 Mar 2005, Ingo Molnar wrote:

>
> * Andrew Morton <akpm@osdl.org> 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?

-- Steve

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