perf: document perfparents

contrib/perf.py

@@ -1164,6 +1164,13 b' def perfstartup(ui, repo, **opts):'
 
 @command(b'perfparents', formatteropts)
 def perfparents(ui, repo, **opts):
+    """benchmark the time necessary to fetch one changeset's parents.
+
+    The fetch is done using the `node identifier`, traversing all object layer
+    from the repository object. The N first revision will be used for this
+    benchmark. N is controlled by the ``perf.parentscount`` config option
+    (default: 1000).
+    """
     opts = _byteskwargs(opts)
     timer, fm = gettimer(ui, opts)
     # control the number of commits perfparents iterates over

tests/test-contrib-perf.t

@@ -129,7 +129,7 b' perfstatus'
                  (no help text available)
    perfnodemap   benchmark the time necessary to look up revision from a cold
                  nodemap
-   perfparents   (no help text available)
+   perfparents   benchmark the time necessary to fetch one changeset's parents.
    perfpathcopies
                  benchmark the copy tracing logic
    perfphases    benchmark phasesets computation