It appears that there is a performance regression for #GrowthExperiments Special:Homepage feature coinciding with the rollout of wmf.28 ([Grafana](https://grafana.wikimedia.org/d/vGq7hbnMz/special-homepage-and-suggested-edits?orgId=1)).
Last 7 days (compared to 7 days prior in orange):
30 day view:
Note that there are several samples recording ~2 seconds to load Special:Homepage on desktop, compared to ~700ms which we usually expect.
The spike coincides with the [scap log entry](https://sal.toolforge.org/production?p=8&q=&d=2022-09-06) for `Started scap: testwikis wikis to 1.39.0-wmf.28 refs T314189`; there is also `multi-DC stage 4: all traffic to appservers-ro, rolling out via puppet 03:24-03:54` ([log entry](https://sal.toolforge.org/log/UJHVEIMB8Fs0LHO5hI1f)) at roughly the same time.
At first glance, I don't see any changes in GrowthExperiments or MediaWiki core that would account for the performance regression.