diff -r 3757a968d63a -r 48394923fbdc contrib/perf.py
--- a/contrib/perf.py	Sun Jan 27 22:32:09 2019 -0500
+++ b/contrib/perf.py	Fri Jan 25 14:52:31 2019 -0500
@@ -535,6 +535,7 @@
 
 @command(b'perfheads', formatteropts)
 def perfheads(ui, repo, **opts):
+    """benchmark the computation of a changelog heads"""
     opts = _byteskwargs(opts)
     timer, fm = gettimer(ui, opts)
     cl = repo.changelog