Re: Why is wmb() a no-op on x86_64?

[Jes Sorensen]

>>>>> "Bryan" == Bryan O'Sullivan <bos@xxxxxxxxxxxxx> writes:

Bryan> On Wed, 2006-01-18 at 17:29 +0100, Andi Kleen wrote:
>> Why do you need the barrier?

Bryan> On x86_64, we fiddle with the MTRRs to enable write combining,
Bryan> which makes a huge difference to performance.  It's not clear
Bryan> to me what we should even do on other architectures, since the
Bryan> only generic entry point that even exposes write combining is
Bryan> pci_mmap_page_range, which is for PCI mmap through userspace,
Bryan> and half the arches I've looked at ignore its write_combine
Bryan> parameter.

A job for mmiowb() perhaps?

Cheers,
Jes
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