Ability to visualize profiling info from v8 profiler

[slonka]

Hi,

V8 profiler has methods called StartProfiling, StopProfiling (https://v8docs.nodesource.com/node-10.6/d2/d34/classv8_1_1_cpu_profiler.html#ab78880137fc43d636cca23c81567b52d). There are modules that allow accessing these methods: https://github.com/hyj1991/v8-profiler-next/blob/master/src/cpu_profile.cc. I created a converter that can convert that format into something that is acceptable by 0x (generates a tree structure similar to the one generated here: https://github.com/davidmarkclements/0x/blob/master/lib/render.js#L19).

Would you be interested in including that functionality? (you can preview the code here: slonka@a9c848c and I'll create a PR if you want)

BTW I'm just wondering why did you only use --prof as a means of collecting stack information? How does it differ from CpuProfiler::StartProfiling?

[mcollina]

Would you be interested in including that functionality? (you can preview the code here: slonka/0x@a9c848c and I'll create a PR if you want)

I think so! Can you add a screenshot here of how that would look like?

BTW I'm just wondering why did you only use --prof as a means of collecting stack information? How does it differ from CpuProfiler::StartProfiling?

I think because we need no native addon to start that. @davidmarkclements definitely knows more!

[slonka]

I think so! Can you add a screenshot here of how that would look like?

Yeah sure. Here is a flamegraph of a simple server responding with a string hello under 10RPS.

To run it you simply invoke:
0x --visualize-v8-profile v8-profiler-output.json

I think because we need no native addon to start that. @davidmarkclements definitely knows more!

I was more interested in the profiling data that is provided. Does --prof call CpuProfiler::StartProfiling underneath?

[mcollina]

@slonka send the PR over. In your PR can you please add an example on how to generate that output?

I was more interested in the profiling data that is provided. Does --prof call CpuProfiler::StartProfiling underneath?

I never investigated in depth. The actual output looks very similar anyway.

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