2022-08-09 Triage Log

A pretty quiet week for performance. Unfortunately, by far the biggest change was a regression introduced by increasing the minimum libc version for linux-gnu targets. The exact reason for why this happened in this case is unclear, and it's not easy to investigate. Luckily, the average regression introduced by this change was 0.4% which is fairly small, and many of the larger regressions were limited to doc builds.

Triage done by @rylev. Revision range: 792bc5a0..cc4dd6fc

Summary:

	mean	max	count
Regressions ❌ (primary)	0.5%	1.4%	146
Regressions ❌ (secondary)	0.8%	1.6%	78
Improvements ✅ (primary)	N/A	N/A	0
Improvements ✅ (secondary)	-2.0%	-4.0%	9
All ❌✅ (primary)	0.5%	1.4%	146

1 Regressions, 2 Improvements, 2 Mixed; 1 of them in rollups 42 artifact comparisons made in total

Regressions

Increase the minimum linux-gnu versions #95026 (Comparison Link)

	mean	max	count
Regressions ❌ (primary)	0.4%	1.6%	137
Regressions ❌ (secondary)	0.7%	1.6%	65
Improvements ✅ (primary)	N/A	N/A	0
Improvements ✅ (secondary)	-0.6%	-0.6%	2
All ❌✅ (primary)	0.4%	1.6%	137

• This is difficult to debug as there was no change to code in the project, just in how things are built.
• Most of the larger regressions are in doc builds where we have slightly higher tolerance for performance issues.
• This means the regressions are something we can probably live with.

Improvements

remove commit_unconditionally #99509 (Comparison Link)

	mean	max	count
Regressions ❌ (primary)	N/A	N/A	0
Regressions ❌ (secondary)	N/A	N/A	0
Improvements ✅ (primary)	-0.5%	-1.0%	8
Improvements ✅ (secondary)	-0.8%	-0.8%	1
All ❌✅ (primary)	-0.5%	-1.0%	8

Rollup of 6 pull requests #100304 (Comparison Link)

	mean	max	count
Regressions ❌ (primary)	N/A	N/A	0
Regressions ❌ (secondary)	1.5%	1.5%	1
Improvements ✅ (primary)	N/A	N/A	0
Improvements ✅ (secondary)	-1.9%	-4.0%	13
All ❌✅ (primary)	N/A	N/A	0

Mixed

Warn about dead tuple struct fields #95977 (Comparison Link)

	mean	max	count
Regressions ❌ (primary)	N/A	N/A	0
Regressions ❌ (secondary)	1.2%	1.5%	3
Improvements ✅ (primary)	N/A	N/A	0
Improvements ✅ (secondary)	-1.4%	-1.6%	6
All ❌✅ (primary)	N/A	N/A	0

• The regressions are only in secondary tests and are more or less a wash (tipping slightly towards more improvements)

Add option to mir::MutVisitor to not invalidate CFG. #100089 (Comparison Link)

	mean	max	count
Regressions ❌ (primary)	0.3%	0.4%	3
Regressions ❌ (secondary)	1.3%	1.5%	6
Improvements ✅ (primary)	N/A	N/A	0
Improvements ✅ (secondary)	-1.5%	-1.5%	1
All ❌✅ (primary)	0.3%	0.4%	3

• This is a small enough regression that I don't think we need to investigate it deeply.
• It seems there‘s more calls in type unification, but I don’t see how this change would impact that.
• Left a comment on the PR