Re: question on memory barrier

[Oliver Neukum]

Am Mittwoch, 24. August 2005 20:22 schrieb linux-os (Dick Johnson):
> > sorry but I'm not sure to understand you...Do you mean that the first write
> > into reg_a pointer will be completed before the second write because they're
> > separated by a (;) ?
> 
> Yes. The compiler must make sure that every effect of all previous
> code and all side-effects are complete at a "sequence-point". There
> are several sequence-points and the most obvious is a ";".

What the compiler may or may not generate is a little beside the point.
You have no guarantee that the CPU will execute these instructions in
the order given. If you need ordered writes use the appropriate barriers,
eg. wmb();
If this is PCI you also need to worry about the bridge caching. You
need to do dummy reads.

	Regards
		Oliver
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