Re: rt file i/o

[Clark Williams <williams@redhat.com>]

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On Wed, 04 Nov 2009 18:32:41 +0100
Tim Blechmann <tim@klingt.org> wrote:

> >> well, if i understand the rt howto correctly, _no_ disc access is
> >> allowed, neither from rt nor from non-rt threads, since it may produce
> >> page faults, which introduce latencies ...
> > 
> > I would be supprised if the rt howto states that page-faults in non-rt
> > threads is a critical problem - that would not significantly impact RT
> > performance - atelast not the worst case - it will (as every other system
> > load) impact the average case. so having a non-rt thread reading disk-files
> > to a buffer and a rt-thread processing this buffer should be perfectly fine.
> 
> that is what i thought for years ... but according to [1] a page fault
> in an rt process freezes the entire process with both rt and non-rt
> threads until the page fault is handled ...
> 

No, we need to get that fixed in the wiki. It may have been the case
that the entire process was frozen while a fault was being handled, but
I don't believe that is the case now. If you're in a thread on core0
and a sibling thread on core1 faults, you shouldn't be impacted unless
you're trying to reference the same memory. 

Clark

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