block, bfq: make sure queue budgets are not below service received
With some unlucky sequences of events, the function bfq_updated_next_req
updates the current budget of a bfq_queue to a lower value than the
service received by the queue using such a budget. Unfortunately, if
this happens, then the return value of the function bfq_bfqq_budget_left
becomes inconsistent. This commit solves this problem by lower-bounding
the budget computed in bfq_updated_next_req to the service currently
charged to the queue.
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 9ea2c4f..b0e8006 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -907,8 +907,10 @@ static void bfq_updated_next_req(struct bfq_data *bfqd,
*/
return;
- new_budget = max_t(unsigned long, bfqq->max_budget,
- bfq_serv_to_charge(next_rq, bfqq));
+ new_budget = max_t(unsigned long,
+ max_t(unsigned long, bfqq->max_budget,
+ bfq_serv_to_charge(next_rq, bfqq)),
+ entity->service);
if (entity->budget != new_budget) {
entity->budget = new_budget;
bfq_log_bfqq(bfqd, bfqq, "updated next rq: new budget %lu",