Bug: 31.05 - 30.31% welcome loadtime / welcome fcp (Linux) regression on Wed August 31 2022
Status: RESOLVED
Priority: P1
Resolution: WONTFIX
Created: 2022-09-06 10:10:05+00:00
Resolved: 2022-10-26 13:35:44+00:00

Perfherder has detected a browsertime performance regression from push [a4c660accc0d7d4c55d01f454b9b2437eac07f57](https://hg.mozilla.org/integration/autoland/pushloghtml?changeset=a4c660accc0d7d4c55d01f454b9b2437eac07f57). As author of one of the patches included in that push, we need your help to address this regression.

### Regressions:

| **Ratio** | **Test** | **Platform** | **Options** | **Absolute values (old vs new)**| 
|--|--|--|--|--| 
| [31%](https://treeherder.mozilla.org/perfherder/graphs?timerange=1209600&series=autoland,3937071,1,13) | [welcome](https://firefox-source-docs.mozilla.org/testing/perfdocs/raptor.html#welcome-c) loadtime | linux1804-64-shippable-qr | fission warm webrender | [40.19](https://firefox-ci-tc.services.mozilla.com/api/queue/v1/task/TWFCgRojSeKUhDGvoRyadg/runs/0/artifacts/public/test_info/browsertime-results.tgz) -> [52.67](https://firefox-ci-tc.services.mozilla.com/api/queue/v1/task/JuBWmDZRQ8y2-Wibf-AoyA/runs/0/artifacts/public/test_info/browsertime-results.tgz) |
| [30%](https://treeherder.mozilla.org/perfherder/graphs?timerange=1209600&series=autoland,3937069,1,13) | [welcome](https://firefox-source-docs.mozilla.org/testing/perfdocs/raptor.html#welcome-c) fcp | linux1804-64-shippable-qr | fission warm webrender | [51.00](https://firefox-ci-tc.services.mozilla.com/api/queue/v1/task/TWFCgRojSeKUhDGvoRyadg/runs/0/artifacts/public/test_info/browsertime-results.tgz) -> [66.46](https://firefox-ci-tc.services.mozilla.com/api/queue/v1/task/JuBWmDZRQ8y2-Wibf-AoyA/runs/0/artifacts/public/test_info/browsertime-results.tgz) |
### Improvements:

| **Ratio** | **Test** | **Platform** | **Options** | **Absolute values (old vs new)**| 
|--|--|--|--|--| 
| [14%](https://treeherder.mozilla.org/perfherder/graphs?timerange=1209600&series=autoland,3914629,1,13)  | [welcome](https://firefox-source-docs.mozilla.org/testing/perfdocs/raptor.html#welcome-c) PerceptualSpeedIndex | windows10-64-shippable-qr | fission warm webrender | 1,299.17 -> 1,117.35 |
| [12%](https://treeherder.mozilla.org/perfherder/graphs?timerange=1209600&series=autoland,3914615,1,13)  | [welcome](https://firefox-source-docs.mozilla.org/testing/perfdocs/raptor.html#welcome-c) ContentfulSpeedIndex | windows10-64-shippable-qr | cold fission webrender | 1,263.92 -> 1,117.76 |
| [9%](https://treeherder.mozilla.org/perfherder/graphs?timerange=1209600&series=autoland,3914610,1,13)  | [welcome](https://firefox-source-docs.mozilla.org/testing/perfdocs/raptor.html#welcome-c) SpeedIndex | windows10-64-shippable-qr | cold fission webrender | 1,229.25 -> 1,123.41 |


Details of the alert can be found in the [alert summary](https://treeherder.mozilla.org/perfherder/alerts?id=35287), including links to graphs and comparisons for each of the affected tests. Please follow our [guide to handling regression bugs](https://wiki.mozilla.org/TestEngineering/Performance/Handling_regression_bugs) and **let us know your plans within 3 business days, or the offending patch(es) may be backed out** in accordance with our [regression policy](https://www.mozilla.org/en-US/about/governance/policies/regressions/).

If you need the profiling jobs you can trigger them yourself from treeherder job view or ask a sheriff to do that for you.

For more information on performance sheriffing please see our [FAQ](https://wiki.mozilla.org/TestEngineering/Performance/FAQ).