CPUs embed a performance monitoring unit (PMU) which we can use to collect data on cache usage (hit/miss) branch predictions, instructions, cycles, etc. those counters can be accessed in Java thanks to the overseer library.

1. Measuring directly from CPU :
Hardware performance
counters
Jean-Philippe BEMPEL
Performance Architect
@jpbempel
http://jpbempel.blogspot.com

2. ●Measuring time
○ System.CurrentTimeMillis()
○ System.nanoTime()
●Timestamps in logs
●Profiling
Measuring

3. ● System.currentTimeMillis()
1ms -> 10-15ms depending on the OS
● System.nanoTime()
500ns -> 1us
Précision

4. ● CPUs embeds PMU (Processing Monitoring Unit)
● Hardware counters on CPU behavior:
○ Cycles
○ Instructions
○ Caches
○ Memory accesses
● predefined or customizable
Compteurs de performance

5. Hiérarchie mémoire

6. échelle de latence

7. ●available on most linux distros
●Allow to access perf counters but allow other things
(profiling, OS counters, …)
●list perf counters: perf list
●Profiler with default counters
perf stat java…
●Customize a perf counter
perf stat -e LLC-load-misses java ...
Perf

8. DEMO
Perf

9. ●java library (JNI - linux only)
●Allow to use all available counters
●Based on libpfm4
○Encodes counters based on CPU
●Profile precisely part of the code of applications
Overseer

10. DEMO
Overseer

11. DEMO
Memory layout: LinkedList

12. DEMO
Memory layout: ArrayList

13. Pipeline

14. ● Overseer library:
○ http://www.peternier.com/projects/overseer/overseer.php
● libpfm4:
○ http://perfmon2.sourceforge.net/
Liens

15. Thanks for your attention.
Questions?