perf sched: Add 'perf sched trace', improve documentation

Alias 'perf sched trace' to 'perf trace', for workflow completeness.

Add a bit of documentation for perf sched.

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

tools/perf/Documentation/perf-sched.txt

@@ -3,16 +3,32 @@ perf-sched(1)
 
 NAME
 ----
-perf-sched - Read perf.data (created by perf record) and display sched output
+perf-sched - Tool to trace/measure scheduler properties (latencies)
 
 SYNOPSIS
 --------
 [verse]
-'perf sched' [-i <file> | --input=file] symbol_name
+'perf sched' {record|latency|replay|trace}
 
 DESCRIPTION
 -----------
-This command reads the input file and displays the latencies recorded.
+There's four variants of perf sched:
+
+  'perf sched record <command>' to record the scheduling events
+  of an arbitrary workload.
+
+  'perf sched latency' to report the per task scheduling latencies
+  and other scheduling properties of the workload.
+
+  'perf sched trace' to see a detailed trace of the workload that
+  was recorded.
+
+  'perf sched replay' to simulate the workload that was recorded
+  via perf sched record. (this is done by starting up mockup threads
+  that mimic the workload based on the events in the trace. These
+  threads can then replay the timings (CPU runtime and sleep patterns)
+  of the workload as it occured when it was recorded - and can repeat
+  it a number of times, measuring its performance.)
 
 OPTIONS
 -------

tools/perf/builtin-sched.c

@@ -1597,7 +1597,7 @@ static int read_events(void)
 }
 
 static const char * const sched_usage[] = {
-	"perf sched [<options>] {record|latency|replay}",
+	"perf sched [<options>] {record|latency|replay|trace}",
 	NULL
 };
 
@@ -1719,6 +1719,11 @@ int cmd_sched(int argc, const char **argv, const char *prefix __used)
 				usage_with_options(replay_usage, replay_options);
 		}
 		__cmd_replay();
+	} else if (!strcmp(argv[0], "trace")) {
+		/*
+		 * Aliased to 'perf trace' for now:
+		 */
+		return cmd_trace(argc, argv, prefix);
 	} else {
 		usage_with_options(sched_usage, sched_options);
 	}