https://treeherder.mozilla.org/perf.html#/compare?originalProject=try&originalRevision=f866c1e6660a2cab858f93685cb5cfc39d32cb81&newProject=try&newRevision=6852198cf76abc21a113ab0f58178e556fccc950&framework=1 compares performance with `PresShell::ComputeBackstopColor()` overridden to return either always white or always transparent. The comparison indicates that webrender performance is significantly better with transparent backstop than with white backstop and this difference explains the regression reported in this bug. Non-webrender performance does not show the same difference. 38b37dfa1f333de0785a1282f487549992698477 has been backed out, for other reasons, and so the performance regression will appear to be corrected. Transparent backstop, however, is an accident waiting to be fixed. (Talos does not draw tabs in the background, possibly based on GTK version.) It is likely to be corrected again.
Bug 1572691 Comment 5 Edit History
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https://treeherder.mozilla.org/perf.html#/compare?originalProject=try&originalRevision=f866c1e6660a2cab858f93685cb5cfc39d32cb81&newProject=try&newRevision=6852198cf76abc21a113ab0f58178e556fccc950&framework=1 compares performance with `PresShell::ComputeBackstopColor()` overridden to return either always white or always transparent. The comparison indicates that webrender performance is significantly better with transparent backstop than with white backstop and this difference explains the regression reported in this bug. Non-webrender performance does not show the same difference. 38b37dfa1f333de0785a1282f487549992698477 has been backed out, for other reasons, and so the performance regression will appear to be corrected. Transparent backstop, however, is an accident waiting to be fixed. (Talos does not draw tabs in the titlebar, possibly based on GTK version.) It is likely to be corrected again.