[PATCH 04/17] block, bfq: recover the "service hole" if enough budget is left

[Kemeng Shi]

If budget left is less than budget need by next request, the activated bfqq
will be expired if it preempts the in-service queue. Avoid to cause useless
overhead to check budget left is enough for next request.

Signed-off-by: Kemeng Shi <shikemeng@xxxxxxxxxxxxxxx>
---
 block/bfq-iosched.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 7b416f9471b3..edbf5c9aeb47 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -1588,13 +1588,15 @@ static bool bfq_bfqq_update_budg_for_activation(struct bfq_data *bfqd,
 
 	/*
 	 * In the next compound condition, we check also whether there
-	 * is some budget left, because otherwise there is no point in
-	 * trying to go on serving bfqq with this same budget: bfqq
-	 * would be expired immediately after being selected for
-	 * service. This would only cause useless overhead.
+	 * is some budget left for next request to serve, because
+	 * otherwise there is no point in trying to go on serving bfqq
+	 * with this same budget: bfqq would be expired immediately
+	 * after being selected for service. This would only cause
+	 * useless overhead.
 	 */
 	if (bfq_bfqq_non_blocking_wait_rq(bfqq) && arrived_in_time &&
-	    bfq_bfqq_budget_left(bfqq) > 0) {
+	    bfq_bfqq_budget_left(bfqq) >=
+	    bfq_serv_to_charge(bfqq->next_rq, bfqq)) {
 		/*
 		 * We do not clear the flag non_blocking_wait_rq here, as
 		 * the latter is used in bfq_activate_bfqq to signal
-- 
2.30.0