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SubjectRe: pthread_mutex_unlock (was Re: sched_yield() makes OpenLDAP slow)
Nick Piggin wrote:
> Howard Chu wrote:
>> scheduling policy at all, the expectation is that the current thread
>> will not continue to run unless there are no other runnable threads
>> in the same process. The other important point here is that the
>> yielding thread is only cooperating with other threads in its
>> process. The 2.6
> No I don't think so. POSIX 1.b where sched_yield is defined are the
> realtime extensions, are they not?
> sched_yield explicitly makes reference to the realtime priority system
> of thread lists does it not? It is pretty clear that it is used for
> realtime processes to deterministically give up their timeslices to
> others of the same priority level.

The fact that sched_yield came originally from the realtime extensions
is just a historical artifact. There was a pthread_yield() function
specifically for threads and it was merged with sched_yield(). Today
sched_yield() is a core part of the basic Threads specification,
independent of the realtime extensions. The fact that it is defined
solely in the language of the realtime priorities is an obvious flaw in
the spec, since the function itself exists independently of realtime
priorities. The objection I raised with the Open Group specifically
addresses this flaw.

> Linux's SCHED_OTHER behaviour is arguably the best interpretation,
> considering SCHED_OTHER is defined to have a single priority level.

It appears that you just read the spec and blindly followed it without
thinking about what it really said and failed to say. The best
interpretation would come from saying "hey, this spec is only defined
for realtime behavior, WTF is it supposed to do for the default
non-realtime case?" and getting a clear definition in the spec.

-- Howard Chu
Chief Architect, Symas Corp.
Director, Highland Sun
OpenLDAP Core Team

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