CpuProfile ->.cpuprofile.

[Jane Chen]

I'm trying to serialize the CpuProfile object to a JSON serialization compatible to Chrome's .cpuprofile file.  The part I'm not clear about is the samples array in the .cpuprofile file:

"head":

{}

,

"startTime": 1611259.054962,

"endTime": 1611262.312964,

"samples": [

2,

3,

3,

3,

So it looks like an integer array, but what are they?  Line numbers?  How do I get it from CpuProfileNode returned from CpuProfile::GetSample()?

Thanks a lot!

[Ben Noordhuis]

"samples" corresponds to the record_samples argument to
v8::StartProfiling::CpuProfiler(). When false, you get the aggregated
hit count. When true, you get data that can be plotted on a timeline.
Put another way, record_samples=false only tells you "how much",
record_samples=true also tells you "when".

The array itself is basically a mapping of CpuProfileNodes from
CpuProfile::GetSample() to integers and sorted by timestamp in
ascending order.

[Jane Chen]

So you mean the integers in the samples array are indexes of CpuProfileNodes?  But does CpuProfileNode have an index?  Still struggling to see how to get the integers in the samples array.

[Ben Noordhuis]

On Wed, Dec 9, 2015 at 8:55 PM, Jane Chen <jxch...@gmail.com> wrote:
> So you mean the integers in the samples array are indexes of
> CpuProfileNodes? But does CpuProfileNode have an index? Still struggling
> to see how to get the integers in the samples array.

You can map them to numeric indexes like this:

int monotonic_counter = 0;
std::map<const v8::CpuProfileNode*, int> nodes;
std::vector<int> samples;
for (int i = 0; i < profile->GetSamplesCount(); i += 1) {
int& sample = nodes[profile->GetSample(i)];
if (sample == 0) sample = ++monotonic_counter;
samples.push_back(sample);
}
// now write out |samples|

If you use an appropriately sized hash table instead of a map you can
bring algorithm complexity down from O(n*lg n) to amortized O(n).
Hope that helps.

[Jane Chen]

Thanks a lot!  It sure helps.

I found CpuProfileNode.GetNodeId().  Maybe that's the pre-computed id which is the same as what you show here?

[Jim Acquavella]

I wish V8 would do this for us.  I'm about to implement this as well, though v8 is crashing soon after I start profiling (addressed in another thread).  

I would recommend you download the Chromium source and look at how it converts from V8's cpu profile data into the file.  See chromium\src\third_party\WebKit\Source\core\inspector\v8\V8ProfilerAgentImpl.cpp for inspiration.

-Jim

[Ben Noordhuis]

On Thu, Dec 10, 2015 at 1:08 AM, Jane Chen <jxch...@gmail.com> wrote:
> Thanks a lot! It sure helps.
>
> I found CpuProfileNode.GetNodeId(). Maybe that's the pre-computed id which
> is the same as what you show here?

Yes, you're right. Now that I look at our code base, we actually use
GetNodeId(). The std::map approach we used in node.js v0.10 / V8 3.14
compatibility code, where that method does not exist.

[Jane Chen]

Great.  Thanks again.

I guess I really should just download the Chromium source code.  But deoptReason is a string, while GetDeoptInfos() returns a vector.  Maybe I'm looking at mismatching v8 versions here?

[Jim Acquavella]

I believe your goal is to write a version of the cpuprofile file that is compatible with the latest Chrome.  In that case, you should just match the current Chromium implementation:

https://chromium.googlesource.com/chromium/src.git/+/master/third_party/WebKit/Source/core/inspector/v8/V8ProfilerAgentImpl.cpp

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[Jim Acquavella]

Now located here:

https://chromium.googlesource.com/chromium/src.git/+/master/third_party/WebKit/Source/platform/v8_inspector/V8HeapProfilerAgentImpl.cpp

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