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author | Davide Zini <davidezini2@gmail.com> | 2023-01-03 17:55:02 +0300 |
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committer | Jens Axboe <axboe@kernel.dk> | 2023-01-30 01:18:33 +0300 |
commit | 2d31c684a053b46f75b230899d00c0f56708243d (patch) | |
tree | 2394e3ad408f6b0ad169039e1ee29b4c20c85f7d /block/bfq-wf2q.c | |
parent | 4fdb3b9f2a280eeea3407321705275fc9a77e3a6 (diff) | |
download | linux-2d31c684a053b46f75b230899d00c0f56708243d.tar.xz |
block, bfq: inject I/O to underutilized actuators
The main service scheme of BFQ for sync I/O is serving one sync
bfq_queue at a time, for a while. In particular, BFQ enforces this
scheme when it deems the latter necessary to boost throughput or
to preserve service guarantees. Unfortunately, when BFQ enforces
this policy, only one actuator at a time gets served for a while,
because each bfq_queue contains I/O only for one actuator. The
other actuators may remain underutilized.
Actually, BFQ may serve (inject) extra I/O, taken from other
bfq_queues, in parallel with that of the in-service queue. This
injection mechanism may provide the ground for dealing also with
the above actuator-underutilization problem. Yet BFQ does not take
the actuator load into account when choosing which queue to pick
extra I/O from. In addition, BFQ may happen to inject extra I/O
only when the in-service queue is temporarily empty.
In view of these facts, this commit extends the
injection mechanism in such a way that the latter:
(1) takes into account also the actuator load;
(2) checks such a load on each dispatch, and injects I/O for an
underutilized actuator, if there is one and there is I/O for it.
To perform the check in (2), this commit introduces a load
threshold, currently set to 4. A linear scan of each actuator is
performed, until an actuator is found for which the following two
conditions hold: the load of the actuator is below the threshold,
and there is at least one non-in-service queue that contains I/O
for that actuator. If such a pair (actuator, queue) is found, then
the head request of that queue is returned for dispatch, instead
of the head request of the in-service queue.
We have set the threshold, empirically, to the minimum possible
value for which an actuator is fully utilized, or close to be
fully utilized. By doing so, injected I/O 'steals' as few
drive-queue slots as possibile to the in-service queue. This
reduces as much as possible the probability that the service of
I/O from the in-service bfq_queue gets delayed because of slot
exhaustion, i.e., because all the slots of the drive queue are
filled with I/O injected from other queues (NCQ provides for 32
slots).
This new mechanism also counters actuator underutilization in the
case of asymmetric configurations of bfq_queues. Namely if there
are few bfq_queues containing I/O for some actuators and many
bfq_queues containing I/O for other actuators. Or if the
bfq_queues containing I/O for some actuators have lower weights
than the other bfq_queues.
Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Davide Zini <davidezini2@gmail.com>
Link: https://lore.kernel.org/r/20230103145503.71712-8-paolo.valente@linaro.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Diffstat (limited to 'block/bfq-wf2q.c')
-rw-r--r-- | block/bfq-wf2q.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/block/bfq-wf2q.c b/block/bfq-wf2q.c index ea4c3d757fdd..7941b6f07391 100644 --- a/block/bfq-wf2q.c +++ b/block/bfq-wf2q.c @@ -493,7 +493,7 @@ static void bfq_active_insert(struct bfq_service_tree *st, bfq_update_active_tree(node); if (bfqq) - list_add(&bfqq->bfqq_list, &bfqq->bfqd->active_list); + list_add(&bfqq->bfqq_list, &bfqq->bfqd->active_list[bfqq->actuator_idx]); bfq_inc_active_entities(entity); } |