40% performance regression SPEC2006/leslie3d on gcc-4_2-branch

Vladimir Makarov vmakarov@redhat.com
Thu Feb 22 18:26:00 GMT 2007


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.




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