AFAIK memory barriers are the architecture specific instructions which restricts the instruction execution in order as received, since otherwise CPU might change the order of execution of instructions for effective use of pipelines or instruction execution optimizations.

Although many times it is required that the instructions to be executed in particular order only in order to prevent the consistency of data and hence memory barriers are required.

Regards,
Piyush
 

2011/3/6 Михаил Кринкин <krinkin.m.u@gmail.com>
You can see linux/Documentation/memory_barriers.txt about barriers in common



i think, that specific definition of __memory_barrier depend on architecture. What file did you found this definition in?
2011/3/6 loody <miloody@gmail.com>

hi all:
I grep kernel source and found cpu_relax is defined as
__memory_barrier(), which seems not defined in kernel source.
At beginning I think it may be the gcc build-in functions, but I
cannot find in the gcc document.
Where and what is that used for?

--
Regards,
miloody

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