tracing/fastboot: add better resolution to initcall debug/tracing

Change the time resolution for initcall_debug to microseconds, from
milliseconds.  This is handy to determine which initcalls you want to work
on for faster booting.

One one of my test machines, over 90% of the initcalls are less than a
millisecond and (without this patch) these are all reported as 0 msecs.
Working on the 900 us ones is more important than the 4 us ones.

With 'quiet' on the kernel command line, this adds no significant overhead
to kernel boot time.
Signed-off-by: NTim Bird <tim.bird@am.sony.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

include/linux/ftrace.h

@@ -217,7 +217,7 @@ struct boot_trace {
 	pid_t			caller;
 	char			func[KSYM_NAME_LEN];
 	int			result;
-	unsigned long long	duration;
+	unsigned long long	duration;		/* usecs */
 	ktime_t			calltime;
 	ktime_t			rettime;
 };

init/main.c

@@ -721,8 +721,8 @@ int do_one_initcall(initcall_t fn)
 	if (initcall_debug) {
 		it.rettime = ktime_get();
 		delta = ktime_sub(it.rettime, it.calltime);
-		it.duration = (unsigned long long) delta.tv64 >> 20;
-		printk("initcall %pF returned %d after %Ld msecs\n", fn,
+		it.duration = (unsigned long long) delta.tv64 >> 10;
+		printk("initcall %pF returned %d after %Ld usecs\n", fn,
 			it.result, it.duration);
 		trace_boot(&it, fn);
 	}