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| author | Paolo Valente <paolo.valente@linaro.org> | 2019-01-29 12:06:26 +0100 |
|---|---|---|
| committer | Jens Axboe <axboe@kernel.dk> | 2019-01-31 12:50:23 -0700 |
| commit | 218cb897be6940b8d18eec9bcb32eaa28f1ae8ee (patch) | |
| tree | b1061e11a7ea7dfb673e336ee0b54c5baf97b924 /block/bfq-iosched.c | |
| parent | 20cd32450bcbec37c6d881b84bdddd8ba047ab01 (diff) | |
| download | linux-218cb897be6940b8d18eec9bcb32eaa28f1ae8ee.tar.gz linux-218cb897be6940b8d18eec9bcb32eaa28f1ae8ee.tar.bz2 linux-218cb897be6940b8d18eec9bcb32eaa28f1ae8ee.zip | |
block, bfq: avoid selecting a queue w/o budget
To boost throughput on devices with internal queueing and in scenarios
where device idling is not strictly needed, bfq immediately starts
serving a new bfq_queue if the in-service bfq_queue remains without
pending I/O, even if new I/O may arrive soon for the latter queue. Then,
if such I/O actually arrives soon, bfq preempts the new in-service
bfq_queue so as to give the previous queue a chance to go on being
served (in case the previous queue should actually be the one to be
served, according to its timestamps).
However, the in-service bfq_queue, say Q, may also be without further
budget when it remains also pending I/O. Since bfq changes budgets
dynamically to fit the needs of bfq_queues, this happens more often than
one may expect. If this happens, then there is no point in trying to go
on serving Q when new I/O arrives for it soon: Q would be expired
immediately after being selected for service. This would only cause
useless overhead. This commit avoids such a useless selection.
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/bfq-iosched.c')
| -rw-r--r-- | block/bfq-iosched.c | 10 |
1 files changed, 9 insertions, 1 deletions
diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c index c7a4a15c7c19..9ea2c4f42501 100644 --- a/block/bfq-iosched.c +++ b/block/bfq-iosched.c @@ -1380,7 +1380,15 @@ static bool bfq_bfqq_update_budg_for_activation(struct bfq_data *bfqd, { struct bfq_entity *entity = &bfqq->entity; - if (bfq_bfqq_non_blocking_wait_rq(bfqq) && arrived_in_time) { + /* + * 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. + */ + if (bfq_bfqq_non_blocking_wait_rq(bfqq) && arrived_in_time && + bfq_bfqq_budget_left(bfqq) > 0) { /* * We do not clear the flag non_blocking_wait_rq here, as * the latter is used in bfq_activate_bfqq to signal |