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

[Linus Torvalds]

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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