Yes what you are saying is also right, since in order to prevent the ordering all the pending memory operations should have completed hence as you mentioned processor stops and make sure all the memory operations are completed.
On Tue, Mar 8, 2011 at 11:59 AM, Mulyadi Santosa <[email protected]>wrote: > On Sun, Mar 6, 2011 at 21:02, loody <[email protected]> wrote: > > 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? > > Hi.. > > are you sure it's memory barrier? I check the source in lxr.linux.no > (2.6.37.3) and cpu_relax is expanded as 'rep' and 'nop' asm > instruction > > but speaking about __memory_barrier(), I find it in > > http://lxr.linux.no/#linux+v2.6.37.3/include/linux/compiler-intel.h#L19...meaning...(at > least for me), it's a macro specificly defined in Intel C compiler > (not gcc which we usually uses). > > IMHO, it does the same as barrier everywhere....processor stop a while > and it make sure any memory operation (especially write) has been > done.... > > -- > regards, > > Mulyadi Santosa > Freelance Linux trainer and consultant > > blog: the-hydra.blogspot.com > training: mulyaditraining.blogspot.com > > _______________________________________________ > Kernelnewbies mailing list > [email protected] > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies >
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