781945 - Improve GC telemetry

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Bill McCloskey [inactive unless it's an emergency] (:billm)]

Attachment: patch

This fixes the problem where GC_MS records the total time between the start and the end of the GC. I considered using a different histogram for this, but since the old one is totally useless, I think we should just replace it.

It also adds a max pause field, which is a little more useful than the GC_SLICE_MS histogram, which records the time of every slice, and so tends to be somewhat optimistic.

I also had it record the time for root marking and gray marking. I don't have a good idea of how long these phases are taking in the wild, so it would be good to get some data on this.

Comment 1

[Andrew McCreight (out of office until 8/21) [:mccr8]]

Comment on attachment 651010 [details] [diff] [review]
patch

Review of attachment 651010 [details] [diff] [review]:
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Nice!

::: toolkit/components/telemetry/TelemetryHistograms.h
@@ +56,4 @@
>  HISTOGRAM(GC_MARK_MS, 1, 10000, 50, EXPONENTIAL, "Time spent running JS GC mark phase (ms)")
>  HISTOGRAM(GC_SWEEP_MS, 1, 10000, 50, EXPONENTIAL, "Time spent running JS GC sweep phase (ms)")
> +HISTOGRAM(GC_MARK_ROOTS_MS, 1, 200, 50, LINEAR, "Time spent running JS GC mark phase (ms)")
> +HISTOGRAM(GC_MARK_GRAY_MS, 1, 200, 50, LINEAR, "Time spent running JS GC mark phase (ms)")

nit: The descriptions of MARK_GRAY needs to be fixed.

Comment 2

[Bill McCloskey [inactive unless it's an emergency] (:billm)]

https://hg.mozilla.org/integration/mozilla-inbound/rev/65bc2e5b574f

Comment 3

[Ed Morley [:emorley]]

https://hg.mozilla.org/mozilla-central/rev/65bc2e5b574f