dm stats: support precise timestamps

Make it possible to use precise timestamps with nanosecond granularity
in dm statistics.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
diff --git a/drivers/md/dm-stats.h b/drivers/md/dm-stats.h
index e7c4984..f1c0956 100644
--- a/drivers/md/dm-stats.h
+++ b/drivers/md/dm-stats.h
@@ -18,6 +18,7 @@
 
 struct dm_stats_aux {
 	bool merged;
+	unsigned long long duration_ns;
 };
 
 void dm_stats_init(struct dm_stats *st);
@@ -30,7 +31,8 @@
 
 void dm_stats_account_io(struct dm_stats *stats, unsigned long bi_rw,
 			 sector_t bi_sector, unsigned bi_sectors, bool end,
-			 unsigned long duration, struct dm_stats_aux *aux);
+			 unsigned long duration_jiffies,
+			 struct dm_stats_aux *aux);
 
 static inline bool dm_stats_used(struct dm_stats *st)
 {