perf/trace/scripting: wakeup-latency script cleanup

Some minor fixes for the wakeup-latency script:

 - Fix nuisance 'use of uninitialized value' warnings

 - Avoid divide-by-zero error

Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
LKML-Reference: <1273466820-9330-5-git-send-email-tzanussi@gmail.com>
Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/scripts/perl/wakeup-latency.pl

@@ -22,8 +22,8 @@ my %last_wakeup;
 
 my $max_wakeup_latency;
 my $min_wakeup_latency;
-my $total_wakeup_latency;
-my $total_wakeups;
+my $total_wakeup_latency = 0;
+my $total_wakeups = 0;
 
 sub sched::sched_switch
 {
@@ -67,8 +67,12 @@ sub trace_end
 {
     printf("wakeup_latency stats:\n\n");
     print "total_wakeups: $total_wakeups\n";
-    printf("avg_wakeup_latency (ns): %u\n",
-	   avg($total_wakeup_latency, $total_wakeups));
+    if ($total_wakeups) {
+	printf("avg_wakeup_latency (ns): %u\n",
+	       avg($total_wakeup_latency, $total_wakeups));
+    } else {
+	printf("avg_wakeup_latency (ns): N/A\n");
+    }
     printf("min_wakeup_latency (ns): %u\n", $min_wakeup_latency);
     printf("max_wakeup_latency (ns): %u\n", $max_wakeup_latency);