cfq-iosched: Charge at least 1 jiffie instead of 1 ns

Commit 9a7f38c4 (cfq-iosched: Convert from jiffies to nanoseconds)
could result in charging just 1 ns to a cgroup submitting IO instead of 1
jiffie we always charged before. It is arguable what is the right amount
to change but for now lets retain the old behavior of always charging at
least one jiffie.

Fixes: 9a7f38c4Signed-off-by: NJan Kara <jack@suse.cz>
Signed-off-by: NJens Axboe <axboe@fb.com>

block/cfq-iosched.c

@@ -1463,7 +1463,8 @@ static inline u64 cfq_cfqq_slice_usage(struct cfq_queue *cfqq,
 		 * a single request on seeky media and cause lots of seek time
 		 * and group will never know it.
 		 */
-		slice_used = max_t(u64, (now - cfqq->dispatch_start), 1);
+		slice_used = max_t(u64, (now - cfqq->dispatch_start),
+					jiffies_to_nsecs(1));
 	} else {
 		slice_used = now - cfqq->slice_start;
 		if (slice_used > cfqq->allocated_slice) {