Re: sched_yield() makes OpenLDAP slow

[Lee Revell <rlrevell@joe-job.com>]

On Sat, 2005-08-20 at 11:38 -0700, Howard Chu wrote:
> But I also found that I needed to add a new 
> yield(), to work around yet another unexpected issue on this system -
> we have a number of threads waiting on a condition variable, and the
> thread holding the mutex signals the var, unlocks the mutex, and then 
> immediately relocks it. The expectation here is that upon unlocking
> the mutex, the calling thread would block while some waiting thread
> (that just got signaled) would get to run. In fact what happened is
> that the calling thread unlocked and relocked the mutex without
> allowing any of the waiting threads to run. In this case the only
> solution was to insert a yield() after the mutex_unlock(). 

That's exactly the behavior I would expect.  Why would you expect
unlocking a mutex to cause a reschedule, if the calling thread still has
timeslice left?

Lee