Bug: 122.22 - 2.73% cnn-ampstories FirstVisualChange / ebay ContentfulSpeedIndex + 22 more (Windows) regression on Fri April 16 2021
Status: RESOLVED
Priority: P2
Resolution: FIXED
Created: 2021-04-20 12:41:21+00:00
Resolved: 2022-03-02 16:43:21+00:00

Perfherder has detected a browsertime performance regression from push [84499c442e82d5b0d09018e7ca0d943647659e6d](https://hg.mozilla.org/integration/autoland/pushloghtml?changeset=84499c442e82d5b0d09018e7ca0d943647659e6d). As author of one of the patches included in that push, we need your help to address this regression.

### Regressions:

| **Ratio** | **Suite** | **Test** | **Platform** | **Options** | **Absolute values (old vs new)**| 
|--|--|--|--|--|--| 
| 122% | cnn-ampstories | FirstVisualChange | windows10-64-shippable-qr | cold live webrender | 45.00 -> 100.00 |
| 85% | cnn-ampstories | FirstVisualChange | windows10-64-shippable-qr | cold live webrender | 45.00 -> 83.33 |
| 27% | cnn-ampstories | fnbpaint | windows10-64-shippable-qr | cold live webrender | 292.71 -> 372.25 |
| 26% | cnn-ampstories | ContentfulSpeedIndex | windows10-64-shippable-qr | cold live webrender | 120.04 -> 150.83 |
| 21% | google-slides | FirstVisualChange | windows10-64-shippable-qr | cold webrender | 787.42 -> 954.50 |
| 19% | cnn-ampstories | loadtime | windows10-64-shippable-qr | cold live webrender | 492.02 -> 583.58 |
| 17% | office | FirstVisualChange | windows10-64-shippable-qr | cold webrender | 1,068.88 -> 1,252.42 |
| 15% | office | FirstVisualChange | windows10-64-shippable-qr | cold webrender | 1,079.83 -> 1,241.08 |
| 14% | cnn-ampstories | fcp | windows10-64-shippable-qr | cold live webrender | 464.83 -> 530.42 |
| 12% | office | SpeedIndex | windows10-64-shippable-qr | cold webrender | 1,156.17 -> 1,300.08 |
|...|...|...|...|...|...|
| 6% | yahoo-mail | ContentfulSpeedIndex | windows10-64-shippable-qr | warm webrender | 319.38 -> 340.08 |
| 6% | instagram | LastVisualChange | windows10-64-shippable-qr | cold webrender | 1,329.75 -> 1,413.75 |
| 5% | google-slides | ContentfulSpeedIndex | windows10-64-shippable-qr | cold webrender | 1,523.42 -> 1,592.00 |
| 4% | office | ContentfulSpeedIndex | windows10-64-shippable-qr | cold webrender | 1,523.04 -> 1,581.33 |
| 3% | ebay | ContentfulSpeedIndex | windows10-64-shippable-qr | cold webrender | 902.67 -> 927.33 |
### Improvements:

| **Ratio** | **Suite** | **Test** | **Platform** | **Options** | **Absolute values (old vs new)**| 
|--|--|--|--|--|--| 
| 34% | twitch | FirstVisualChange | windows10-64-shippable-qr | cold webrender | 198.33 -> 130.50 |
| 28% | youtube | dcf | windows10-64-shippable | warm | 1,194.08 -> 862.00 |
| 28% | youtube | dcf | windows10-64-shippable-qr | warm webrender | 1,207.12 -> 874.38 |
| 16% | netflix | LastVisualChange | windows10-64-shippable | cold | 1,580.00 -> 1,320.00 |
| 16% | instagram | loadtime | windows10-64-shippable-qr | cold webrender | 1,550.62 -> 1,308.12 |
|...|...|...|...|...|...|
| 7% | youtube | LastVisualChange | windows10-64-shippable | cold | 2,786.67 -> 2,583.33 |


Details of the alert can be found in the [alert summary](https://treeherder.mozilla.org/perfherder/alerts?id=29739), 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) will be backed out** in accordance with our [regression policy](https://www.mozilla.org/en-US/about/governance/policies/regressions/).

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