Jan Hubicka wrote:
Grigory Zagorodnev wrote:
Mark Mitchell wrote:
Excellent question; I should have asked for that as well. If 4.2 has
gained on 4.1 in other respects, the 4.7% drop might represent a smaller
regression relative to 4.1.
There is the 4.2 (r120817) vs. 4.1.2 release FP performance comparison
numbers. SPECfp_base2006 of gcc 4.2 has 19% performance gain over 4.1.2.
Thank you for the measurements.
In that case, I think we have absolutely nothing to worry about for
4.2.0. Whether we deliver 19% SPECfp, 23% SPECfp, or 15% SPECfp
improvements isn't so important; all of those numbers are a vast
improvement over 4.1.x. Given that, I think we should just leave
Danny's conservative changes in, and not worry.
It should be understood that the large improvement on Cores is special
case caused by adding a generic model and CPU specific tuning (We
originally measured 28% speedup on P4 and SPECfp2000 just for that
change). Situation can be less optimistic on other (sub)targets.
Still we made important progress on SPECfp in the 4.x series, so 4%
slowdown would not bring us to performance of GCC's from mid 90's as 4%
slowdown on SPECint would perhaps do...
I remember nocona tunning gave 30% improvement SPECFp2000 for Intel
nocona in 64 bit mode in comparison with the default x86_64 gcc tuning
(for k8). So such big improvement is definetly mostly from new
-mtune=generic.
