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

[Benjamin LaHaise]

On Tue, Feb 28, 2006 at 11:20:24AM -0800, Bryan O'Sullivan wrote:
> So if we just use wmb(), we incur a 16-cycle penalty on every packet we
> send.  This has a deleterious and measurable effect on performance.

sfence doesn't guarantee that the write will be flushed, especially if 
the chipset gets involved.  The only way to do that is the same way any 
pci write can be flushed, which is to read from a register on the device 
in question.

		-ben
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