On Wed, 18 Jun 2008, Jeremy Fitzhardinge wrote:
>
> It's not cmpxchg, just xchg.
> In other words, is:
>
> lock btr $_PAGE_BIT_RW, (%rbx)
Well, we can actually do it as
lock andl $~_PAGE_RW,(%rbx)
although we haven't bothered (I've wanted several times to make
clear_bit() do that, but have never gotten around to it - mainly because
old gcc versions didn't work with __builtin_constant_p() in inline
functions - so you have to do the macro from hell)
And yes, the "lock andl" should be noticeably faster than the xchgl.
Linus
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