I can't even see what performance number has changed, because harbourmaster only shows the tail of the log.

From https://phabricator.haskell.org/harbormaster/build/4553:

10 bytes allocated value is too high:
11 Expected haddock.Cabal(normal) bytes allocated: 6710234312 +/-5%
12 Lower bound haddock.Cabal(normal) bytes allocated: 6374722596 
13 Upper bound haddock.Cabal(normal) bytes allocated: 7045746028 
14 Actual haddock.Cabal(normal) bytes allocated: 7417348832 
15 Deviation haddock.Cabal(normal) bytes allocated: 10.5 %
16 *** unexpected stat test failure for haddock.Cabal(normal)
17 bytes allocated value is too high:
18 Expected haddock.compiler(normal) bytes allocated: 36740649320 +/-10%
19 Lower bound haddock.compiler(normal) bytes allocated: 33066584388 
20 Upper bound haddock.compiler(normal) bytes allocated: 40414714252 
21 Actual haddock.compiler(normal) bytes allocated: 40681382656 
22 Deviation haddock.compiler(normal) bytes allocated: 10.7 %
23 *** unexpected stat test failure for haddock.compiler(normal)