* Esben Nielsen <[EMAIL PROTECTED]> wrote:
> Yeah, after sending that mail I realized I accepted this fact way
> back... But I disagree in that it is easy to avoid not write-lcling
> the mm semaphore: A simple malloc() might lead to a mmap() call
> creating trouble. Am I right?
yeah - that's why "hard RT" apps generally either preallocate all memory
in advance, or use special, deterministic allocators. And for "soft RT"
it's all a matter of degree.
> > But mainline should not be bothered with this.
>
> I disagree. You lay a large burdon on the users of PI futexes to avoid
> write locking the mm semaphore. PI boosting those writers would be a
> good idea even in the mainline.
only if it can be done without slowing down all the much more important
uses of the MM semaphore.
> 1) How much slower would the pi_rw_mutex I suggested really be? As far
> as I see there is only an overhead when there is congestion. I can not
> see that that overhead is much larger than a non-PI boosting
> implementation.
it could be measured, but it's certainly not going to be zero.
> 2) I know that execution time isn't bounded in the main-line - that is
> why -rt is needed. But it is _that_ bad? How low can you get your
> latencies with preemption on on a really busy machine?
on mainline? It can get arbitrarily large (read: seconds) in essence.
Ingo
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