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SubjectRe: [PATCH]: Fix SMP-reordering race in mark_buffer_dirty

On Wed, 2 Apr 2008, Andrew Morton wrote:
> But then the test-and-set of an already-set flag would newly cause the
> cacheline to be dirtied, requiring additional bus usage to write it back?
> The CPU's test-and-set-bit operation could of course optimise that away in
> this case. But does it?

No, afaik no current x86 uarch will optimize away the write on a locked
instuction if it turns out to be unnecessary.

Can somebody find a timing reason to have the ugly code?


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