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block, bfq: make sure queue budgets are not below service received

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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>
This commit is contained in:
Paolo Valente 2019-01-29 12:06:27 +01:00 committed by Jens Axboe
parent 218cb897be
commit f3218ad8c6
1 changed files with 4 additions and 2 deletions
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6
block/bfq-iosched.c
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@ -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",