[Vm-dev] CogVM performance

[Levente Uzonyi]

Hi All,

I saw that some of my benchmarks produce different results when running on 
PharoVM instead of CogVM, and I was wondering why. I ran #tinyBenchmarks 
from the same image on both VMs and the results were surprising:

"CogVM 3343" '904593639 bytecodes/sec; 46368169 sends/sec'
"Pharo vm50" '941176470 bytecodes/sec; 120698445 sends/sec'

Slightly more bytecodes, and a lot more sends. I tried playing with 
compiler flags, but with no luck, so I came to the conclusion that the 
difference comes from somewhere else. I checked where the PharoVM was 
forked from CogVM (somewhere around 2014-06-10), so I downloaded a version 
of CogVM from around that time: CogVM 3048.

And the results are '932604735 bytecodes/sec; 118660385 sends/sec'.

Somewhere between 3048 and 3343 the performance has dropped significantly 
(sends/sec). Note that this is not something that's only visible in micro 
benchmarks.

Does anyone know why?


Levente