Re: Real-Time Preemption and RCU

[Ingo Molnar]

* Bill Huey <bhuey@xxxxxxxx> wrote:

> I'd like to note another problem. Mingo's current implementation of
> rt_mutex (super mutex for all blocking synchronization) is still
> missing reader counts and something like that would have to be
> implemented if you want to do priority inheritance over blocks.

i really have no intention to allow multiple readers for rt-mutexes. We
got away with that so far, and i'd like to keep it so. Imagine 100
threads all blocked in the same critical section (holding the read-lock)
when a highprio writer thread comes around: instant 100x latency to let
all of them roll forward. The only sane solution is to not allow
excessive concurrency. (That limits SMP scalability, but there's no
other choice i can see.)

	Ingo
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