[LLVMdev] [PATCH] FoldingSetNodeID: use MurmurHash2 instead of SuperFastHash

[Gregory Petrosyan]

On Sat, Feb 06, 2010 at 04:51:15PM -0800, Chandler Carruth wrote:
> While I've not reviewed the patch in too much detail, it looks
> promising. Can you run some end-to-end benchmarks to make sure that
> cache pressure in the full program or other variables not accounted
> for in a micro-benchmark don't dominate performance? Specifically the
> nightly tester includes a number of real programs and machinery to
> measure total compile time.

Ok, now with some kinda-hard numbers!

          murmurhash2                |           superfasthash
                                     |
- 6.6404 seconds (6.6697 wall clock) | 6.6204 seconds (6.8557 wall clock) 
+ 2.6722 seconds (2.7064 wall clock) | 2.7962 seconds (2.7502 wall clock)
+ 8.6725 seconds (8.6662 wall clock) | 8.7526 seconds (8.7162 wall clock)
+ 2.7362 seconds (2.7729 wall clock) | 2.8242 seconds (2.8146 wall clock)
+ 1.4281 seconds (1.4068 wall clock) | 1.4761 seconds (1.4198 wall clock)
+ 4.3163 seconds (4.3392 wall clock) | 4.3683 seconds (4.3969 wall clock)
                                     |
+ 6.6804 seconds (6.6916 wall clock) | 6.7804 seconds (6.6950 wall clock) 
+ 2.7682 seconds (2.7342 wall clock) | 2.7802 seconds (2.7321 wall clock)
- 8.7365 seconds (8.9505 wall clock) | 8.6965 seconds (8.7124 wall clock)
+ 2.7962 seconds (2.7812 wall clock) | 2.8282 seconds (2.8049 wall clock)
+ 1.3881 seconds (1.4103 wall clock) | 1.4001 seconds (1.4103 wall clock)
- 4.3843 seconds (4.3509 wall clock) | 4.3723 seconds (4.3714 wall clock)
                                     |
+ 6.5724 seconds (6.7971 wall clock) | 6.6684 seconds (6.6465 wall clock) 
+ 2.6401 seconds (2.7378 wall clock) | 2.6682 seconds (2.7965 wall clock)
+ 8.7005 seconds (8.7068 wall clock) | 8.7766 seconds (8.8452 wall clock)
+ 2.7282 seconds (2.7680 wall clock) | 2.7762 seconds (2.7904 wall clock)
- 1.4561 seconds (1.4230 wall clock) | 1.4201 seconds (1.4184 wall clock)
- 4.4523 seconds (4.3754 wall clock) | 4.4003 seconds (4.3706 wall clock)

This table was obtaind by running 3 times 'make TEST=nightly report.html -j2
&& l Output/ | grep info | xargs cat | grep 'Total Execution Time' >> timings
&& make clean' or something like that, on MultiSource/Applications/ClamAV.

It looks like FoldingSetNodeID is not the most performance-critical part of
LLVM, but changing the hash algorithm help a bit.

        Gregory