Re: I made a flame graph renderer for git's trace2 output

> On Fri, May 10, 2019 at 05:09:58PM +0200, Ævar Arnfjörð Bjarmason wrote:
>
>> As noted in TODOs in the script there's various stuff I'd like to do
>> better, and this also shows how we need a lot more trace regions to get
>> granular data.
>
> Hmm. My gut reaction was: doesn't "perf record -g make test" already
> give us that granular data? I know "perf" isn't available everywhere,
> but the idea of the FlameGraph repo is that it takes input from a lot of
> sources (though I don't know if it supports any Windows-specific formats
> yet, which is presumably a point of interesting to trace-2 authors).
>
> But having generated such a flamegraph, it's not all that helpful. It
> mainly tells us that we spend a lot of time on fork/exec. Which is no
> surprise, since the test suite is geared not towards heavy workloads,
> but lots of tiny functionality tests.
>
> TBH, I'm not sure that flame-graphing the test suite is going to be all
> that useful in the long run. It's going to be heavily weighted by the
> types of things the test suite does. Flamegraphs are good for
> understanding where your time is going for a particular workload, but
> the workload of the test suite is not that interesting.
>
> And once you do have a particular workload of interest that you can
> replay, then I think the granular "perf" results really can be helpful.
>
> I think the trace2 flamegraph would be most useful if you were
> collecting across a broad spectrum of workloads done by a user. You
> _can_ do that with perf or similar tools, but it can be a bit awkward.
> I do wonder how painful it would be to alias "git" to "perf record git"
> for a day or something.