[PATCH 3 of 6 "] perf: document perfparents

[Pierre-Yves David]

# HG changeset patch
# User Pierre-Yves David <pierre-yves.david at octobus.net>
# Date 1553517838 -3600
#      Mon Mar 25 13:43:58 2019 +0100
# Node ID 0f03ddf89818a3561dcd9b7a186ba7bcd2d10ed3
# Parent  9ba4809996b5ce769376a86cf88ef8f2b844b806
# EXP-Topic perf-run
# Available At https://bitbucket.org/octobus/mercurial-devel/
#              hg pull https://bitbucket.org/octobus/mercurial-devel/ -r 0f03ddf89818
perf: document perfparents

diff --git a/contrib/perf.py b/contrib/perf.py
--- a/contrib/perf.py
+++ b/contrib/perf.py
@@ -1164,6 +1164,13 @@ def perfstartup(ui, repo, **opts):
 
 @command(b'perfparents', formatteropts)
 def perfparents(ui, repo, **opts):
+    """benchmark the time necessary to fetch one changesets 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
diff --git a/tests/test-contrib-perf.t b/tests/test-contrib-perf.t
--- a/tests/test-contrib-perf.t
+++ b/tests/test-contrib-perf.t
@@ -129,7 +129,7 @@ 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 changesets parents.
    perfpathcopies
                  benchmark the copy tracing logic
    perfphases    benchmark phasesets computation