lockstat: Add usage info to Documentation/lockstat.txt

Add usage info to Documentation/lockstat.txt
Signed-off-by: Frank Rowand <frank.rowand@am.sony.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <4B05BE7D.30500@am.sony.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

Documentation/lockstat.txt

@@ -62,8 +62,20 @@ applicable).
 It also tracks 4 contention points per class. A contention point is a call site
 that had to wait on lock acquisition.
 
+ - CONFIGURATION
+
+Lock statistics are enabled via CONFIG_LOCK_STATS.
+
  - USAGE
 
+Enable collection of statistics:
+
+# echo 1 >/proc/sys/kernel/lock_stat
+
+Disable collection of statistics:
+
+# echo 0 >/proc/sys/kernel/lock_stat
+
 Look at the current lock statistics:
 
 ( line numbers not part of actual output, done for clarity in the explanation