Status: Untriaged
Owner: ----
New issue 4406 by [email protected]: profiler has huge impact on
performance for some code (mac)
https://code.google.com/p/v8/issues/detail?id=4406
Version: chrome 44.0.2403.157
OS: OSX 10.10.5
Architecture: x64
What steps will reproduce the problem?
1. Load attached html file in chrome. It outputs several timings of two
function (avg and foo) which take roughly the same amount of time (~1ms on
my machine).
2. Observe times (A)
3. Open devtools, start a profile, reload to rerun
4. Observe times (B)
5. Close devtools
6. Reload page
7. Observe times (C)
What is the expected output?
I expect the times to be the same across A,B,C. This is the case on my
linux workstation - avg and foo each take around 1ms in every case.
What do you see instead?
On my macbook pro foo always takes around 1ms. At time A avg also takes
1ms. But at time B (with the profiler running), avg takes 14ms.
And THEN at time C (after a reload! with no profiler!) avg STILL takes
14ms. To me this is the most terrifying part and the reason it took many
hours yesterday to understand that this wasn't a real issue in my code (I
was switching back and forth between profiling and instrumented
before/after timings).
Note you can also run test.js directly in d8 (I built from head on 8/31/15)
and observe the same slowdown with / without --prof.
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