Re: [PATCH v9 06/19] qspinlock: prolong the stay in the pending bit path

[Peter Zijlstra]

On Thu, Apr 17, 2014 at 09:46:04PM -0400, Waiman Long wrote:
> BTW, I didn't test out your atomic_test_and_set() change. Did it provide a
> noticeable performance benefit when compared with cmpxchg()?

I've not tested that I think. I had a hard time showing that cmpxchg
loops were slower, but once I did, I simply replaced all cmpxchg loops
with unconditional ops where possible.

The machine that was big enough to show it lived in a lab half way
around the world and using it was a right pain in the ass, so I didn't
use it more than I absolutely had to.
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