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

[Linus Torvalds]

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?

		Linus
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