Re: sched_yield() makes OpenLDAP slow

[Nick Piggin]

Robert Hancock wrote:

> I fail to see how sched_yield is going to be very helpful in this 
> situation. Since that call can sleep from a range of time ranging from 
> zero to a long time, it's going to give unpredictable results.

Well, not sleep technically, but yield the CPU for some undefined
amount of time.

> It seems to me that this sort of thing is why we have POSIX pthread 
> synchronization primitives.. sched_yield is basically there for a 
> process to indicate that "what I'm doing doesn't matter much, let other 
> stuff run". Any other use of it generally constitutes some kind of hack.

In SCHED_OTHER mode, you're right, sched_yield is basically meaningless.

In a realtime system, there is a very well defined and probably useful
behaviour.

Eg. If 2 SCHED_FIFO processes are running at the same priority, One can
call sched_yield to deterministically give the CPU to the other guy.

--
SUSE Labs, Novell Inc.

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