Re: [RFC PATCH 0/5] futex: introduce an optimistic spinning futex

Ingo Molnar
2014-07-21T21:18:11Z

* Waiman Long <Waiman.Long@hp.com> wrote:

> Testing done on a 4-socket Westmere-EX boxes with 40 cores (HT off)
> showed the following performance data (average kops/s) with various
> load factor (number of pause instructions) used in the critical
> section using an userspace mutex microbenchmark.
>
> Threads Load Waiting Futex Spinning Futex %Change
> ------- ---- ------------- -------------- -------
> 256 1 6894 8883 +29%
> 256 10 3656 4912 +34%
> 256 50 1332 4358 +227%
> 256 100 792 2753 +248%
> 10 1 6382 4838 -24%
> 10 10 3614 4748 +31%
> 10 50 1319 3900 +196%
> 10 100 782 2459 +214%
> 2 1 7905 7194 -9.0%
> 2 10 4556 4717 +3.5%
> 2 50 2191 4167 +90%
> 2 100 1767 2407 +36%

So the numbers look interesting - but it would be _really_ important
to provide noise/sttdev figures in a sixth column as well (denoted in
percentage units, not in benchmark units), so that we know how
significant a particular speedup (or slowdown) is.

Thanks,

Ingo