Re: [Linux-ia64] Re: web page on O(1) scheduler

[Jan Harkes]

On Wed, Jun 04, 2003 at 09:13:43AM +0200, Mike Galbraith wrote:
> Using sched_yield() as a mutex is exactly the same as using a party line 
> for private conversation.

I actually used sched_yield for the 'inverse' mutex case. One thread was
pretty much exclusively holding a mutex, but other threads sometimes try
to get through the same critical section and block on mutex_lock. 

The first thread then occasionally does,

    mutex_unlock()
    sched_yield()
    mutex_lock()

Without the sched_yield, other threads never get a chance to wake up and
grab the mutex before the mutex hogging thread is back in the critical
section.

This is ofcourse the simple explanation, this was actually part of a
wrapper around pthreads that needed to provide non-concurrent
co-routines that in specific situations could run concurrently for a bit
to do DNS lookups and such.

Not sure how different semantics affect this because I went with a
different solution a while ago.

Jan