[ltt-dev] [URCU PATCH] caa: do not generate code for rmb/wmb on x86_64, rmb on i686

[Paolo Bonzini]

On 09/05/2011 05:12 PM, Mathieu Desnoyers wrote:
>> In userspace we can assume no accesses to write-combining memory occur,
>> >  and also that there are no non-temporal load/stores (people would presumably
>> >  write those with assembly or intrinsics and put appropriate lfence/sfence
>> >  manually).  So rmb and wmb are no-ops on x86.
>
> What about memory barriers for DMA with devices ? For these, we might
> want to define cmm_wmb/rmb and cmm_smp_wmb/rmb differently (keep the
> fences for DMA accesses).

Yes, splitting wmb/rmb and smp_wmb/rmb makes sense.

Paolo