* Borislav Petkov <b...@alien8.de> wrote:
> On Sat, Jun 29, 2013 at 04:56:30PM -0700, Wedson Almeida Filho wrote:
> > On Fri, Jun 28, 2013 at 7:09 AM, Borislav Petkov <b...@alien8.de> wrote:
> >
> > > Btw, do we have any perf data showing any improvements from this patch?
> >
> > I wrote a simple test the measures the time it takes to acquire and
> > release an uncontended mutex (i.e., we always take the fast path)
> > 100k times. I ran it a few times, the original code averages
> > 2.743436ms, and the new code averages 2.101098ms, so it's about 23%
> > improvement.
>
> Microbenchmark results tend to be misleading in such situations. Rather,
> it would be much closer to reality if you traced a real workload like a
> simple kernel build, for example, with and without your patch.
Not sure - the main thing we want to know is whether it gets faster. The
_amount_ will depend on things like precise usage patterns, caching, etc.
- but rarely does a real workload turn a win like this into a loss.
> I.e., something like
>
> perf stat --repeat 5 ./build-kernel.sh
>
> and take a look at what the perfcouters are saying in both cases.
Hm, the noise of such a workload will very likely drown out improvements
that are in the cycle scale.
Thanks,
Ingo
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