Re: [PATCH] Yielding processor resources during lock contention

[Nick Piggin]

Zwane Mwaikambo wrote:
> On Sat, 11 Sep 2004, Andrew Morton wrote:

> > Now, maybe Paul has tied himself into sufficiently tangly locking knots
> > that in some circumstances he needs to spin on the lock and cannot schedule
> > away.  But he can still use a semaphore and spin on down_trylock.
> >
> > Confused by all of this.
>
>
> Well currently it just enables preempt and spins like a mad man until the 
> lock is free. The idea is to allow preempt to get some scheduling done 
> during the spin.. But! if you accept this patch today, you get the 
> i386 version which will allow your processor to halt until a write to the 
> lock occurs whilst allowing interrupts to also trigger the preempt 
> scheduling, much easier on the caches.

That's the idea though isn't it? If your locks are significantly more
expensive than a context switch and associated cache trashing, use a
semaphore, hypervisor or no.

I presume the hypervisor switch much incur the same sorts of costs as
a context switch?
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