Talk from Pharodays 2017. Video: https://www.youtube.com/watch?v=lRQ447XI6Hc

1. Pharo VM
performance
Clement Bera

2. Myself
• Clément Béra
• 2011-2013: Engineer on the Pharo VM
• 2013-2017: PhD student
• Optimisations of the Pharo VM JIT compiler

3. 0
2
4
6
8
10
12
14
16
Interpreter
2005
Stack
2009
Cog V1
2010
Cog V2
2011
Spur
2014
Sista
future
Binary tree benchmark

4. 0
2
4
6
8
10
12
14
16
Interpreter
2005
Stack
2009
Cog V1
2010
Cog V2
2011
Spur
2014
Sista
future
Binary tree benchmark
Pharo 5
2016

5. Plan
• Pharo 5 (stable)
• First time we out benched most competitors
• Pharo 6 (released next week ???)
• Pharo 7

6. Code execution GC

7. GC
• Pharo 5
• New memory manager Spur
• Pharo 6
• New compactor
• Pharo 7
• Incremental GC ???

8. Pharo 5: Spur
• Efficient scavenges
• In most applications, most GC time is now in
scavenges
Code execution GC

9. Pharo 6: New compactor
Loading a 200 Mb Moose Model in 250 Mb image
February April
Total time 2 min
1 min
2 sec
Time in
Full GC
1 min 2 sec
Full GC
avg pause
15 sec 0.5 sec
Time in
scavenge
15 sec 15 sec

10. Pharo 6: New compactor
Loading a 200 Mb Moose Model in 250 Mb image
February April
Total time 2 min
1 min
2 sec
Time in
Full GC
1 min 2 sec
Full GC
avg pause
15 sec 0.5 sec
Time in
scavenge
15 sec 15 sec
<- GC tuning gets
it down to 5 sec

11. Pharo 7: Incremental GC ??
• Full GC pauses: ~500 ms at ~500Mb
• Java default GC at 200ms soft real time
• Solution
• Incremental marking
• Incremental compaction

12. Code execution
• Pharo 5:
• Spur got 1.8x
• Pharo 6:
• Polishing and micro-optimisations
• Pharo 7:
• Sista gets 1.5x-5x

13. Pharo 5: Spur 1.8x
• Class table speeds-up look-up caches
• New immediate objects
• 22 bits hash

14. Pharo 6
• Register allocation improvements
• Two path compilation
• Frameless code for setter-like methods

15. Sista: Pharo 7 ?
• Program introspection
• Speculate on types based on previous runs
• Optimize frequently used code
• Deoptimize and reoptimize code incorrectly
speculated

16. Goals
• Program readability
• Performance

17. Program readability
1 to: array size do: [ :i | (array at: i) yourself ].
array do: [ :elem | elem yourself ].
array do: #yourself.

18. Program readability
1 to: array size do: [ :i | (array at: i) yourself ].
array do: [ :elem | elem yourself ].
array do: #yourself.
0 2 5 20
87M/
sec
28M/
sec
13M/
sec
3.7M
/sec
15M/
sec
21M/
sec
10M/
sec
3.9M
/sec
94M/
sec
40M/
sec
22M/
sec
6.5M
/sec

19. Performance
0 1 2 3 4 5 6
A*
ThreadRing
SpectralNorm
JSJSON
BinaryTree
DeltaBlue
Richards
TCAP
Kmeans
Sista
Pharo

20. Getting stable
• Support most development workflow
• Support image recompilation
• Integration has started

21. In-image design
Smalltalk image
Virtual machine
Cogit
CompiledCode to native code
Machine-specific optimisations
Scorch
CompiledCode to CompiledCode
Smalltalk-specific optimisations
CompiledCode
(persisted across start-ups)
native functions
(discarded on shut-down)
Baseline JIT
Optimising JIT

22. Missing
• IDE support
• Debugger
• Methods to show
• Stability, testing

23. Are you interested ?
• Incremental GC ?
• VM performance ?
• VM features ?
• Come and talk to us !

24. We are looking for…
• Use-cases showing what to improve
• Large real-world benchmarks
• Contributors
• Investment

25. Conclusion
• Pharo 5: Fastest VM
• Pharo 6: Polishing
• Pharo 7: Going further