[Python-Dev] False alarm: big performance hit in the past few days (original) (raw)

Skip Montanaro skip@pobox.com
Wed, 3 Apr 2002 23:26:01 -0600

I found the problem. You'll be glad to know it wasn't with the Python code. It turned out to be compiler flags. When I was benchmarking on March 31, I was specifically setting OPT to something like

-O3 -DSMALL_REQUEST_THRESHOLD=256

Today, I left SMALL_REQUEST_THRESHOLD alone. Since the default optimization level is -O3, I wasn't specifying OPT at all. The default is "-g -O3".

With specific setting of OPT to just -O3, I get these performance numbers:

cvs up -D 2002-03-31 12:00

This machine benchmarks at 5652.91 pystones/second
Pystone(1.1) time for 100000 passes = 17.81
This machine benchmarks at 5614.82 pystones/second
Pystone(1.1) time for 100000 passes = 17.88
This machine benchmarks at 5592.84 pystones/second
278.18user 0.39system 5:11.91elapsed 89%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (400major+3942minor)pagefaults 0swaps

cvs up -A

Pystone(1.1) time for 100000 passes = 17.8
This machine benchmarks at 5617.98 pystones/second
Pystone(1.1) time for 100000 passes = 18.04
This machine benchmarks at 5543.24 pystones/second
Pystone(1.1) time for 100000 passes = 17.85
This machine benchmarks at 5602.24 pystones/second
278.95user 0.26system 4:51.27elapsed 95%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (404major+3941minor)pagefaults 0swaps

so it appears nothing has changed performance-wise since the 31st.

Apparently, addition of debugging symbols exacts a pretty significant toll on performance now. I don't recall that being the case in the past. Perhaps this feature is something new with gcc3. Makes me think perhaps -g should be deleted from the default OPT setting. I'm pretty sure one of the reasons Stallman used to give for always including -g in compiles in the old days (when the only GNU programs were, practically speaking, gcc, gdb and emacs) was that you got debugging capability without taking a performance hit.

Skip