Messages in this thread | | | Date | Mon, 24 Jul 2017 10:44:55 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v6 0/2] x86: Implement fast refcount overflow protection |
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On Mon, Jul 24, 2017 at 04:38:06PM +1000, Michael Ellerman wrote:
> What I'm not entirely clear on is what the best trade off is in terms of > overhead vs checks. The summary of behaviour between the fast and full > versions you promised Ingo will help there I think.
That's something that's probably completely different for PPC than it is for x86. Both because your primitive is LL/SC and thus the saturation semantics we need a cmpxchg loop for are more natural in your case anyway, and the fact that your LL/SC is horrendously slow in any case.
Also, I still haven't seen an actual benchmark where our cmpxchg loop actually regresses anything, just a lot of yelling about potential regressions :/
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