perf lock: Account for lock average wait time

While perf-lock currently reports both the total wait time and the
number of contentions, it doesn't explicitly show the average wait time.
Having this value immediately in the report can be quite useful when
looking into performance issues.

Furthermore, allowing report to sort by averages is another handy
feature to have - and thus do not only print the value, but add it to
the lock_stat structure.

Signed-off-by: Davidlohr Bueso <[e-mail]>
Cc: Aswin Chandramouleeswaran <[e-mail]>
Cc: Frederic Weisbecker <[e-mail]>
Cc: Hitoshi Mitake <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/Documentation/perf-lock.txt

···
 -k::
 --key=<value>::
         Sorting key. Possible values: acquired (default), contended,
-        wait_total, wait_max, wait_min.
+	avg_wait, wait_total, wait_max, wait_min.
 
 INFO OPTIONS
 ------------

tools/perf/builtin-lock.c

···
 
 	unsigned int		nr_readlock;
 	unsigned int		nr_trylock;
+
 	/* these times are in nano sec. */
+	u64                     avg_wait_time;
 	u64			wait_time_total;
 	u64			wait_time_min;
 	u64			wait_time_max;
···
 
 SINGLE_KEY(nr_acquired)
 SINGLE_KEY(nr_contended)
+SINGLE_KEY(avg_wait_time)
 SINGLE_KEY(wait_time_total)
 SINGLE_KEY(wait_time_max)
 
···
 struct lock_key keys[] = {
 	DEF_KEY_LOCK(acquired, nr_acquired),
 	DEF_KEY_LOCK(contended, nr_contended),
+	DEF_KEY_LOCK(avg_wait, avg_wait_time),
 	DEF_KEY_LOCK(wait_total, wait_time_total),
 	DEF_KEY_LOCK(wait_min, wait_time_min),
 	DEF_KEY_LOCK(wait_max, wait_time_max),
···
 
 	seq->state = SEQ_STATE_ACQUIRED;
 	ls->nr_acquired++;
+	ls->avg_wait_time = ls->nr_contended ? ls->wait_time_total/ls->nr_contended : 0;
 	seq->prev_event_time = sample->time;
 end:
 	return 0;
···
 
 	seq->state = SEQ_STATE_CONTENDED;
 	ls->nr_contended++;
+	ls->avg_wait_time = ls->wait_time_total/ls->nr_contended;
 	seq->prev_event_time = sample->time;
 end:
 	return 0;
···
 	pr_info("%10s ", "acquired");
 	pr_info("%10s ", "contended");
 
+	pr_info("%15s ", "avg wait (ns)");
 	pr_info("%15s ", "total wait (ns)");
 	pr_info("%15s ", "max wait (ns)");
 	pr_info("%15s ", "min wait (ns)");
···
 		pr_info("%10u ", st->nr_acquired);
 		pr_info("%10u ", st->nr_contended);
 
+		pr_info("%15" PRIu64 " ", st->avg_wait_time);
 		pr_info("%15" PRIu64 " ", st->wait_time_total);
 		pr_info("%15" PRIu64 " ", st->wait_time_max);
 		pr_info("%15" PRIu64 " ", st->wait_time_min == ULLONG_MAX ?
···
 	};
 	const struct option report_options[] = {
 	OPT_STRING('k', "key", &sort_key, "acquired",
-		    "key for sorting (acquired / contended / wait_total / wait_max / wait_min)"),
+		    "key for sorting (acquired / contended / avg_wait / wait_total / wait_max / wait_min)"),
 	/* TODO: type */
 	OPT_END()
 	};