1637318 - Some GC telemetry histograms are poorly configured

Status: RESOLVED FIXED

(Core :: JavaScript: GC, task, P3)

Description

[Jon Coppeard (:jonco)]

Looking at the GC telemetry in preparation for bug 1636419 I noticed that several histograms have their range configured in such a way that most of their samples end up in the same bucket. This means we are not getting very accurate data from them.

One example is GC_MARK_ROOTS_MS:

https://telemetry.mozilla.org/new-pipeline/dist.html#!cumulative=0&end_date=2020-05-10&include_spill=0&keys=__none__!__none__!__none__&max_channel_version=nightly%252F78&measure=GC_MARK_ROOTS_MS&min_channel_version=nightly%252F75&processType=*&product=Firefox&sanitize=1&sort_by_value=0&sort_keys=submissions&start_date=2020-05-04&table=0&trim=1&use_submission_date=0

(I guess it's good that this is usually so quick!)

There may be various reasons for this. Maybe we used to include more work under this phase, or maybe we just got faster. But we should fix this. That will probably involve creating parallel histograms and expiring the existing ones in a later release.

This affects the following histograms:

• GC_MARK_ROOTS_MS
• GC_MARK_GRAY_MS
• GC_MARK_RATE
• GC_BUDGET_MS
• GC_PRETENURE_COUNT

Comment 2

[Jon Coppeard (:jonco)]

Attachment: Bug 1637318 - Add GC_MARK_ROOTS_US telemetry and mark GC_MARK_ROOTS_MS for expiry r?sfink

Most samples are between 0 and 1 ms so replace with measurement in microseconds.

Comment 3

[Jon Coppeard (:jonco)]

Attachment: Bug 1637318 - Add GC_MARK_GRAY_MS_2 telemetry and mark GC_MARK_GRAY_MS for expiry r?sfink

Depends on D75520

Comment 4

[Jon Coppeard (:jonco)]

Attachment: Bug 1637318 - Add GC_MARK_RATE_2 telemetry and mark GC_MARK_RATE for expiry r?sfink

Depends on D75522

Comment 5

[Jon Coppeard (:jonco)]

Attachment: Bug 1637318 - Add GC_BUDGET_MS_2 telemetry and mark GC_BUDGET_MS for expiry r?sfink

Depends on D75523

Comment 6

[Jon Coppeard (:jonco)]

Attachment: Bug 1637318 - Add GC_PRETENURE_COUNT_2 telemetry and mark GC_PRETENURE_COUNT for expiry r?sfink

Depends on D75524

Comment 7

[Jon Coppeard (:jonco)]

Attachment: data_collection_request.txt

Requesting data review.

Comment 8

[Chris H-C :chutten]

Comment on attachment 9149333 [details]
data_collection_request.txt

DATA COLLECTION REVIEW RESPONSE:

    Is there or will there be documentation that describes the schema for the ultimate data set available publicly, complete and accurate?

Yes. This collection is Telemetry and Glean so is documented in its definitions file [Histograms.json](https://hg.mozilla.org/mozilla-central/file/tip/toolkit/components/telemetry/Histograms.json) and the [Probe Dictionary](https://telemetry.mozilla.org/probe-dictionary/) and [metrics.yaml](https://hg.mozilla.org/mozilla-central/file/tip/toolkit/components/telemetry/geckoview/streaming/metrics.yaml) and [engine-gecko's metrics documentation](https://github.com/mozilla-mobile/android-components/blob/master/components/browser/engine-gecko-nightly/docs/metrics.md).

    Is there a control mechanism that allows the user to turn the data collection on and off?

Yes. This collection is can be controlled through Firefox Desktop's Preferences or Firefox Preview's Preferences.

    If the request is for permanent data collection, is there someone who will monitor the data over time?

Yes, :jonco is responsible.

    Using the category system of data types on the Mozilla wiki, what collection type of data do the requested measurements fall under?

Category 1, Technical.

    Is the data collection request for default-on or default-off?

Default on for all channels.

    Does the instrumentation include the addition of any new identifiers?

No.

    Is the data collection covered by the existing Firefox privacy notice?

Yes.

    Does there need to be a check-in in the future to determine whether to renew the data?

No. This collection is permanent.

---
Result: datareview+

Comment 9

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/639c7c4c355c
Add GC_MARK_ROOTS_US telemetry and mark GC_MARK_ROOTS_MS for expiry r=sfink
https://hg.mozilla.org/integration/autoland/rev/c0389e13a612
Add GC_MARK_GRAY_MS_2 telemetry and mark GC_MARK_GRAY_MS for expiry r=sfink
https://hg.mozilla.org/integration/autoland/rev/4f905a241359
Add GC_MARK_RATE_2 telemetry and mark GC_MARK_RATE for expiry r=sfink
https://hg.mozilla.org/integration/autoland/rev/9888d95d59ec
Add GC_BUDGET_MS_2 telemetry and mark GC_BUDGET_MS for expiry r=sfink
https://hg.mozilla.org/integration/autoland/rev/06a2edc40fb1
Add GC_PRETENURE_COUNT_2 telemetry and mark GC_PRETENURE_COUNT for expiry r=sfink

Comment 10

[Natalia Csoregi [:nataliaCs]]

https://hg.mozilla.org/mozilla-central/rev/639c7c4c355c
https://hg.mozilla.org/mozilla-central/rev/c0389e13a612
https://hg.mozilla.org/mozilla-central/rev/4f905a241359
https://hg.mozilla.org/mozilla-central/rev/9888d95d59ec
https://hg.mozilla.org/mozilla-central/rev/06a2edc40fb1