This is the mail archive of the
gcc-patches@gcc.gnu.org
mailing list for the GCC project.
Re: [PATCH] Change PRED_LOOP_EXIT from 85 to 92
On Sun, Dec 24, 2017 at 09:12:56AM +0000, Richard Sandiford wrote:
> Segher Boessenkool <segher@kernel.crashing.org> writes:
> > On Fri, Dec 22, 2017 at 04:53:47PM -0600, David Esparza wrote:
> >> With a value of 85 GCC has a CPU performance degradation of 11%,
> >> reverting PRED_LOOP_EXIT to 92 this degradation disappear.
> >> Those values where measured by running c-ray ray-tracer that is a
> >> floating point benchmark that runs out of L1 cache.
> >
> > Why is this single benchmark more important than everything else?
> >
> > https://patchwork.ozlabs.org/patch/637073/
>
> "Everything" else? :-) It sounds from Andrew's reply like it wasn't
> a win on other benchmarks too.
Yeah... But at least Martin tested spec2006, instead of one single
tiny non-representative program.
> Neither covering message has really explained why the previous value was
> too low/high, but maybe that's just the way it goes with these tuning
> parameters...
It would be nice if they explained how they tested things.
Segher