On 12/24/2017 05:03 AM, Segher Boessenkool wrote: > On Sun, Dec 24, 2017 at 09:12:56AM +0000, Richard Sandiford wrote: >> Segher Boessenkool <seg...@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. Agreed. I can't see any way for this patch to go forward without some explanation of why it helps this particular c-ray implementation and some data showing it's not hurtful on a wider suite of benchmarks.
Jeff
