--- a/contrib/perf.py	Sat Jun 09 22:38:29 2018 +0900
+++ b/contrib/perf.py	Wed Jul 11 10:46:15 2018 +0200
@@ -774,6 +774,10 @@
 
 @command('perfmanifest', [], 'REV')
 def perfmanifest(ui, repo, rev, **opts):
+    """benchmark the time to read a manifest from disk and return a usable
+    dict-like object
+
+    Manifest caches are cleared before retrieval."""
     timer, fm = gettimer(ui, opts)
     ctx = scmutil.revsingle(repo, rev, rev)
     t = ctx.manifestnode()