Re: [PATCH 13/15] x86: add cmpxchg_flag() variant

[Christoph Lameter]

On Tue, 23 Aug 2011, H. Peter Anvin wrote:

> On 08/23/2011 03:15 PM, Jeremy Fitzhardinge wrote:
> >
> > However, having prototyped it, I dunno, it doesn't really seem like much
> > of a win for all the extra code it adds.  I just can't get too excited
> > about an extra test instruction adjacent to a monster like a locked
> > cmpxchg.  The jump variant avoids the test, but gcc still generates some
> > pretty bogus stuff:
> >
>
> A compare is hardly a big cost, as you're quite correctly pointing out.

Could become relatively costly if the cmpxchg is not locked or the compare
involves comparing multiple words.

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