PM / sleep: Measure the time of filesystems syncing

Measure the filesystems sync time during system sleep more precisely.

Among other things, this allows the pr_cont() to be dropped from
ksys_sync_helper() and makes automatic system suspend and hibernation
profiling somewhat more straightforward.
Signed-off-by: Harry Pan <harry.pan@intel.com>
[ rjw: Changelog ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

kernel/power/main.c

@@ -54,9 +54,14 @@ EXPORT_SYMBOL_GPL(unlock_system_sleep);
 
 void ksys_sync_helper(void)
 {
-	pr_info("Syncing filesystems ... ");
+	ktime_t start;
+	long elapsed_msecs;
+
+	start = ktime_get();
 	ksys_sync();
-	pr_cont("done.\n");
+	elapsed_msecs = ktime_to_ms(ktime_sub(ktime_get(), start));
+	pr_info("Filesystems sync: %ld.%03ld seconds\n",
+		elapsed_msecs / MSEC_PER_SEC, elapsed_msecs % MSEC_PER_SEC);
 }
 EXPORT_SYMBOL_GPL(ksys_sync_helper);