Re: [PATCH] Document Linux's memory barriers

[H. Peter Anvin]

Followup to:  <28393.1141823992@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>
By author:    David Howells <dhowells@xxxxxxxxxx>
In newsgroup: linux.dev.kernel
> 
> However, on i386, for example, you've actually got at least two different I/O
> access domains, and I don't know how they impinge upon each other (IN/OUT vs
> MOV).
> 

You do, but those aren't the ones.

What you have is instead MOVNT versus everything else.  IN/OUT are
total sledgehammers, as they imply not only nonposted operation, but
the instruction implies wait for completion; this is required since
IN/OUT support emulation via SMI.

	-hpa
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