Re: [PATCH] 2.4.0-prerelease: preemptive kernel.

[Andi Kleen]

On Thu, Jan 04, 2001 at 11:32:11PM +1100, Anton Blanchard wrote:
>  
> > I think a better way to proceed would be to make semaphores a bit more 
> > intelligent and turn them into something like adaptive spinlocks and use
> > them more where appropiate (currently using semaphores usually causes
> > lots of context switches where some could probably be avoided). Problem
> > is that for some cases like your producer-consumer pattern (which has been
> > used previously in unreleased kernel code BTW) it would be a pessimization
> > to spin, so such adaptive locks would probably need a different name.
> 
> Like solaris adaptive mutexes? It would be interesting to test,
> however considering read/write semaphores are hardly ever used these
> days we want to be sure they are worth it before adding yet another
> synchronisation primitive.

A bit similar, yes, but much simpler @-)

The problem is that current Linux semaphores are very costly locks -- they
always cause a context switch.

-Andi