doc/dev: add note about intro of perf counters

Add a note to the "perf counter" section of doc/dev/perf_counters.rst
that explains that this feature was introduced in the Reef release of
Ceph. This note will prevent us from accidentally backporting
perf-counter-related PRs to Quincy.

Signed-off-by: Zac Dover <zac.dover@proton.me>
(cherry picked from commit 55e41bc679aeee9119dc815b456bb76880f61ea2)

diff --git a/doc/dev/perf_counters.rst b/doc/dev/perf_counters.rst
index 1bcc6120e4af92f4a02616b52955418e50d95231..3080330bd12402f685c4aef67ecb4b17922da43c 100644 (file)
--- a/doc/dev/perf_counters.rst
+++ b/doc/dev/perf_counters.rst
@@ -4,6 +4,8 @@
  Perf counters
 ===============
 
+.. note:: Perf counters were introduced in the Reef release of Ceph.
+
 The perf counters provide generic internal infrastructure for gauges and counters.  The counted values can be both integer and float. There is also an "average" type (normally float) that combines a sum and num counter which can be divided to provide an average.
 
 The intention is that this data will be collected and aggregated by a tool like ``collectd`` or ``statsd`` and fed into a tool like ``graphite`` for graphing and analysis.  Also, note the :doc:`../mgr/prometheus` and the :doc:`../mgr/telemetry`.