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SubjectRe: [patch 0/9] mutex subsystem, -V4


On Mon, 26 Dec 2005, Arjan van de Ven wrote:
>
> > hm. 16 CPUs hitting the same semaphore at great arrival rates. The cost
> > of a short spin is much less than the cost of a sleep/wakeup. The machine
> > was doing 100,000 - 200,000 context switches per second.
>
> interesting.. this might be a good indication that a "spin a bit first"
> mutex slowpath for some locks might be worth implementing...

No, please don't.

Almost always it's a huge sign that the locking is totally broken.

And yes, the fix was to _fix_ the ext3 locking. Not to make semaphores
spin. The ext3 locking was using a semaphore for totally the wrong
reasons, it made zero sense at all.

I think it's fixed now.

Linus
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