Re: [PATCH] Define wc_wmb, a write barrier for PCI write combining

[Roland Dreier]

    Jes> Could you explain why the current mmiowb() API won't suffice
    Jes> for this?  It seems that this is basically trying to achieve
    Jes> the same thing.

I don't believe mmiowb() is at all the same thing.  mmiowb() is all
about ordering writes between _different_ CPUs without incurring the
cost of flushing posted writes by issuing a read on the bus.  wc_wmb()
would just act like a true wmb(), even when using write-combining
regions on x86 -- in other words, there would be no cross-CPU synchronization.

 - R.
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