1211287 - Profiler should show (and exclude) time spent idle.

Status: RESOLVED DUPLICATE of bug 1152839

(DevTools :: Performance Tools (Profiler/Timeline), defect)

Description

[Jukka Jylänki]

Attachment: performance_profiler.png

When profiling a page that runs with good performance and a large portion of the time is spent idle, the profiler is currently not able to distinguish that time, and it makes the application look as if there was a mysterious performance hog inside the platform code.

To examine, visit https://dl.dropboxusercontent.com/u/40949268/emcc/06_SkeletalAnimation/06_SkeletalAnimation.html

and run a profile. The page runs at good 60fps on the tested system, however the profile is showing that 74.43% of total time is spent in "Gecko", which makes it look as if there is a huge performance problem in Firefox itself.

It would be good if the profiler
 1) had a special node "Idle" which accumulated the time that the browser process was sleeping to wait for an event.
 2) had a checkbox to show/hide the idle time, and recompute the percentages either with this idle time included or excluded. Sometimes one is profiling a workload that is only able to saturate, say, 30% of the CPU, and it would be nice to ignore the 70% of idle time, and rescale that remaining actual 30% workload time to correspond to 100% of the time. Btw, geckoprofiler.xpi is able to do this for any node, i.e. one can select a node in the call tree, and examine the subtree, which scales the time spent in that node as 100% and the subnodes are presented relative to that parent. That is a very powerful visualization tool.

Comment 1

[Nick Fitzgerald [:fitzgen] [⏰PST; UTC-8]]

Yup, definitely want this. Turns out that its a little harder than we expected to get this information reliably, so we need to find some time to do it Properly(tm).