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

[Andi Kleen]

On Wednesday 01 March 2006 20:43, Bryan O'Sullivan wrote:

> > Implementing the fences in the way your're suggesting would be very costly
> > because it could make them potentially stall for thousands of cycles.
> 
> But it *doesn't*.  On existing CPUs and systems, today, the phantom
> worse-case semantics you are conjuring up simply do not exist.  If
> someone builds such an asinine system, the right approach is to handle
> it once it exists.

Normally we write code to the defined architecture.

Relying on undocumented side effects of instructions as you're trying
to do here is not very reliable and would likely cause breakage later.

Especially not for encoding it in the general Linux interface.

-Andi
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