block, bfq: increase time window for waker detection

Tests on slower machines showed current window to be way too
small. This commit increases it.
Tested-by: Jan Kara <jack@suse.cz>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/bfq-iosched.c

@@ -1931,7 +1931,7 @@ static void bfq_add_request(struct request *rq)
 		if (bfqd->last_completed_rq_bfqq &&
 		    !bfq_bfqq_has_short_ttime(bfqq) &&
 		    ktime_get_ns() - bfqd->last_completion <
-		    200 * NSEC_PER_USEC) {
+		    4 * NSEC_PER_MSEC) {
 			if (bfqd->last_completed_rq_bfqq != bfqq &&
 			    bfqd->last_completed_rq_bfqq !=
 			    bfqq->waker_bfqq) {