perf tools: Clarify the output of perf sched map.

In output of perf sched map, any shortname of thread will be explained
at the first time when it appear.

Example:
              *A0       228836.978985 secs A0 => perf:23032
          *.   A0       228836.979016 secs B0 => swapper:0
           .  *C0       228836.979099 secs C0 => migration/3:22
  *A0      .   C0       228836.979115 secs
   A0      .  *.        228836.979115 secs

But B0, which is explained as swapper:0 did not appear in the
left part of output. Instead, we use '.' as the shortname of
swapper:0. So the comment of "B0 => swapper:0" is not easy to
understand.

This patch clarify the output of perf sched map with not allocating
one letter-number shortname for swapper:0 and print ". => swapper:0"
as the explanation for swapper:0.

Example:
              *A0       228836.978985 secs A0 => perf:23032
          * .  A0       228836.979016 secs .  => swapper:0
            . *B0       228836.979099 secs B0 => migration/3:22
  *A0       .  B0       228836.979115 secs
   A0       . * .       228836.979115 secs
   A0     *C0   .       228836.979225 secs C0 => ksoftirqd/2:18
   A0     *D0   .       228836.979236 secs D0 => rcu_sched:7

Signed-off-by: Dongsheng <yangds.fnst@cn.fujitsu.com>
Acked-by: Ingo Molnar <mingo@kernel.org>
Link: http://lkml.kernel.org/r/1399354741-19522-1-git-send-email-yangds.fnst@cn.fujitsu.com
[ small style fixes to make checkpatch happy ]
Signed-off-by: Jiri Olsa <jolsa@kernel.org>

tools/perf/builtin-sched.c

@@ -1300,17 +1300,25 @@ static int map_switch_event(struct perf_sched *sched, struct perf_evsel *evsel,
 
 	new_shortname = 0;
 	if (!sched_in->shortname[0]) {
-		sched_in->shortname[0] = sched->next_shortname1;
-		sched_in->shortname[1] = sched->next_shortname2;
-
-		if (sched->next_shortname1 < 'Z') {
-			sched->next_shortname1++;
+		if (!strcmp(thread__comm_str(sched_in), "swapper")) {
+			/*
+			 * Don't allocate a letter-number for swapper:0
+			 * as a shortname. Instead, we use '.' for it.
+			 */
+			sched_in->shortname[0] = '.';
+			sched_in->shortname[1] = ' ';
 		} else {
-			sched->next_shortname1='A';
-			if (sched->next_shortname2 < '9') {
-				sched->next_shortname2++;
+			sched_in->shortname[0] = sched->next_shortname1;
+			sched_in->shortname[1] = sched->next_shortname2;
+
+			if (sched->next_shortname1 < 'Z') {
+				sched->next_shortname1++;
 			} else {
-				sched->next_shortname2='0';
+				sched->next_shortname1 = 'A';
+				if (sched->next_shortname2 < '9')
+					sched->next_shortname2++;
+				else
+					sched->next_shortname2 = '0';
 			}
 		}
 		new_shortname = 1;
@@ -1322,12 +1330,9 @@ static int map_switch_event(struct perf_sched *sched, struct perf_evsel *evsel,
 		else
 			printf("*");
 
-		if (sched->curr_thread[cpu]) {
-			if (sched->curr_thread[cpu]->tid)
-				printf("%2s ", sched->curr_thread[cpu]->shortname);
-			else
-				printf(".  ");
-		} else
+		if (sched->curr_thread[cpu])
+			printf("%2s ", sched->curr_thread[cpu]->shortname);
+		else
 			printf("   ");
 	}