926610 - Improve async profiler startup feature list: "stackwalk"

Status: RESOLVED WORKSFORME

(Core :: Gecko Profiler, defect)

Description

[Jed Davis [:jld] ⟨⏰|UTC-7⟩ ⟦he/him⟧]

So let's have a separate bug for turning on stack walking.  Bug 916106 is a source of concern.

+++ This bug was initially created as a clone of Bug #919078 +++

Starting the profiler asynchronously will be more useful if more features are enabled; in particular, "js" and "stackwalk" (or "leaf" on platforms where stack walking isn't available) are ones that I predict most users of the profiler will expect, and which the existing profiler-start-on-startup mechanism enables.

Comment 1

[Jed Davis [:jld] ⟨⏰|UTC-7⟩ ⟦he/him⟧]

Bug 916106 has landed.  Is there anything else that needs to happen to turn on stack walking by default on ARM B2G?

Comment 2

[Benoit Girard (:BenWa)]

What's the difference in CPU usage by having this on by default when idle?

Comment 3

[Jed Davis [:jld] ⟨⏰|UTC-7⟩ ⟦he/him⟧]

On keon, with the CPU set to maximum speed (1008 MHz) instead of being dynamically scaled:

Not profiling: 0.4%
Profiling with js+leaf: 6.7%
Profiling with js+stackwalk: 7.0%

That's the main thread of the main b2g process, sitting at the home screen, with the usual screen blanking on inactivity disabled.

Comment 4

[Jed Davis [:jld] ⟨⏰|UTC-7⟩ ⟦he/him⟧]

Forgot to mention: measured by adding the "utime" and "stime" fields (14 and 15) from /proc/N/stat, and measured over 300 seconds.

Comment 5

[Benoit Girard (:BenWa)]

That's impressive. Alright lets turn it on!

Comment 6

[Jed Davis [:jld] ⟨⏰|UTC-7⟩ ⟦he/him⟧]

Attachment: bug926610-stackwalk-on-async-hg0.diff

Comment 7

[Jed Davis [:jld] ⟨⏰|UTC-7⟩ ⟦he/him⟧]

Comment on attachment 820502 [details] [diff] [review]
bug926610-stackwalk-on-async-hg0.diff

We're going to roll this into bug 925111, since that patch completely overwrites the code that would be changed here.

Comment 8

[Markus Stange [:mstange]]

The profiler features for async profiler starts seem to be read from a "profiler.options" file and are no longer hardcoded.
But I think this method of starting the profiler from a signal handler was only ever used on B2G anyway and can probably removed.