Messages in this thread | | | Date | Wed, 24 Aug 2011 08:54:40 -0500 (CDT) | From | Christoph Lameter <> | Subject | Re: [PATCH 13/15] x86: add cmpxchg_flag() variant |
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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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