1519752 - Record profiler overhead data

Status: RESOLVED FIXED

(Core :: Gecko Profiler, enhancement, P3)

Description

[Gerald Squelart (he/him) (not at Mozilla since 2022-09-15)]

It should be very easy and inexpensive to record some information about the time spent in the profiler.

At first, it could be kept hidden in Gecko profiles for our own use, to help us figure out sources of profiler performance issues, and to find regressions when we are modifying the profiler core code.
While hidden, we can easily change what we want to record based on experience using it.

Once stable, some of this data could be presented in the front-end, to indicate how much
the profiler may have influenced the software being profiled.

The prototype I'm working on currently records the following data:

 "profilerOverhead_UNSTABLE": {
  "schema": {"time": 0, "locking": 1, "cleaning": 2, "counters": 3, "threads": 4},
  "data": [
   [138.67270000000002, 0.0013, 0.00019999999999999998, 0.0024, 0.1003],
   [140.49980000000002, 0.0025, 0.0003, 0.00039999999999999996, 0.0522],
   "...",
   [6383.7972, 0.0019, 0.00009999999999999999, 0.00019999999999999998, 0.0291],
   [6385.7934, 0.0015, 0.00019999999999999998, 0.00019999999999999998, 0.034100000000000005]
  ],
  "statistics": {
   "profiledInterval": 6247.1206999999995,
   "overheadDurations": 169.3540000000005,
   "overheadPercentage": 0.027109128850351893,
   "samplingCount": 3133,
   "minInterval": 1.8271000000000015,
   "maxInterval": 2.095399999999927,
   "meanInterval": 1.9946106960408683,
   "minOverhead": 0.0023,
   "maxOverhead": 0.4188,
   "meanOverhead": 0.05405489945738924,
   "minLockings": 0.0006,
   "maxLockings": 0.056100000000000004,
   "meanLockings": 0.0025483242898180713,
   "minCleaning": 0,
   "maxCleaning": 0.058699999999999995,
   "meanCleaning": 0.0003978295563357614,
   "minCounter": 0.00009999999999999999,
   "maxCounter": 0.0593,
   "meanCounter": 0.0005486434727098368,
   "minThread": 0.0013,
   "maxThread": 0.414,
   "meanThread": 0.05056010213852527
  }
 }

(Intentionally not explaining each property, because I'm hoping they're self-explanatory -- please ask for better names if needed.)

Suggestions welcome.

Comment 1

[Gerald Squelart (he/him) (not at Mozilla since 2022-09-15)]

Attachment: Bug 1519752 - Profiler overhead measurements - r?mstange

Record some profiling overhead data, stored in Gecko profiles under
"profilerOverhead_UNSTABLE". Unstable for now as it will first be used
internally to help with profiler performance, and find regressions in upcoming
work; The choice of data may change as we explore what we need.

Eventually this data could be presented in the front-end, to indicate how much
the profiler may have influenced the profiled software.

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/8765e788de8b
Profiler overhead measurements - r=mstange

Comment 3

[Cosmin Sabou [:CosminS]]

https://hg.mozilla.org/mozilla-central/rev/8765e788de8b