Re: [PATCH 2/2] ix86: atomic64 assembly improvements

[H. Peter Anvin]

On 01/19/2012 06:50 AM, Jan Beulich wrote:
> > It doesn't have anything to do with caches on or off.
>
> How does it not? If any part of the bus topology is only 32 bits wide,
> a 64-bit read or write simply can't be executed atomically without
> asserting LOCK#.

Furthermore, if you're going down that rathole then we can't even trust 
MOV (nor, for that matter, can you trust LOCK in a lot of 
circumstances.)  In short, you need to be extremely careful about what 
you do to uncached memory *at all* (and you need to know exactly what is 
behind this bus) but pessimizing these kinds of construct for that 
reason is wrong in the extreme.

	-hpa

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