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SubjectRe: [patch] SMP alternatives
Alan Cox wrote:
> On Mer, 2005-11-23 at 13:36 -0800, Linus Torvalds wrote:
>
>>>have to add PAT support which we need to do anyway we would get a world
>>>where on uniprocessor lock prefix only works on addresse targets we want
>>>it to - ie pci_alloc_consistent() pages.
>>
>>No. That would be wrong.
>>
>>The thing is, "lock" is useless EVEN ON SMP in user space 99% of the time.
>
>
> Now I see what you are aiming at, yes that makes vast amounts of sense
> and since AMD have the "no lock effect" bit for general case maybe they
> can
>

What it really comes down to (virtualization or not!) is whether or not
the OS can guarantee that nothing else is messing with memory at the
same time.

This is potentially different from process to process (because of page
table differences) and from kernel to user space (because of the User
bit in the page tables.)

-hpa


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