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Message-Id: <88084DDA-A705-4CFA-887E-021FC5DD89E9@linaro.org>
Date: Sat, 26 Nov 2022 17:28:44 +0100
From: Paolo Valente <paolo.valente@...aro.org>
To: Damien Le Moal <damien.lemoal@...nsource.wdc.com>
Cc: Jens Axboe <axboe@...nel.dk>,
linux-block <linux-block@...r.kernel.org>,
linux-kernel <linux-kernel@...r.kernel.org>,
Arie van der Hoeven <arie.vanderhoeven@...gate.com>,
Rory Chen <rory.c.chen@...gate.com>,
Gabriele Felici <felicigb@...il.com>,
Carmine Zaccagnino <carmine@...minezacc.com>
Subject: Re: [PATCH V6 1/8] block, bfq: split sync bfq_queues on a
per-actuator basis
> Il giorno 21 nov 2022, alle ore 01:18, Damien Le Moal <damien.lemoal@...nsource.wdc.com> ha scritto:
>
> On 11/4/22 01:26, Paolo Valente wrote:
>> Single-LUN multi-actuator SCSI drives, as well as all multi-actuator
>> SATA drives appear as a single device to the I/O subsystem [1]. Yet
>> they address commands to different actuators internally, as a function
>> of Logical Block Addressing (LBAs). A given sector is reachable by
>> only one of the actuators. For example, Seagate’s Serial Advanced
>> Technology Attachment (SATA) version contains two actuators and maps
>> the lower half of the SATA LBA space to the lower actuator and the
>> upper half to the upper actuator.
>>
>> Evidently, to fully utilize actuators, no actuator must be left idle
>> or underutilized while there is pending I/O for it. The block layer
>> must somehow control the load of each actuator individually. This
>> commit lays the ground for allowing BFQ to provide such a per-actuator
>> control.
>>
>> BFQ associates an I/O-request sync bfq_queue with each process doing
>> synchronous I/O, or with a group of processes, in case of queue
>> merging. Then BFQ serves one bfq_queue at a time. While in service, a
>> bfq_queue is emptied in request-position order. Yet the same process,
>> or group of processes, may generate I/O for different actuators. In
>> this case, different streams of I/O (each for a different actuator)
>> get all inserted into the same sync bfq_queue. So there is basically
>> no individual control on when each stream is served, i.e., on when the
>> I/O requests of the stream are picked from the bfq_queue and
>> dispatched to the drive.
>>
>> This commit enables BFQ to control the service of each actuator
>> individually for synchronous I/O, by simply splitting each sync
>> bfq_queue into N queues, one for each actuator. In other words, a sync
>> bfq_queue is now associated to a pair (process, actuator). As a
>> consequence of this split, the per-queue proportional-share policy
>> implemented by BFQ will guarantee that the sync I/O generated for each
>> actuator, by each process, receives its fair share of service.
>>
>> This is just a preparatory patch. If the I/O of the same process
>> happens to be sent to different queues, then each of these queues may
>> undergo queue merging. To handle this event, the bfq_io_cq data
>> structure must be properly extended. In addition, stable merging must
>> be disabled to avoid loss of control on individual actuators. Finally,
>> also async queues must be split. These issues are described in detail
>> and addressed in next commits. As for this commit, although multiple
>> per-process bfq_queues are provided, the I/O of each process or group
>> of processes is still sent to only one queue, regardless of the
>> actuator the I/O is for. The forwarding to distinct bfq_queues will be
>> enabled after addressing the above issues.
>>
>> [1] https://www.linaro.org/blog/budget-fair-queueing-bfq-linux-io-scheduler-optimizations-for-multi-actuator-sata-hard-drives/
>>
>> Signed-off-by: Gabriele Felici <felicigb@...il.com>
>> Signed-off-by: Carmine Zaccagnino <carmine@...minezacc.com>
>> Signed-off-by: Paolo Valente <paolo.valente@...aro.org>
>> ---
>> block/bfq-cgroup.c | 95 ++++++++++++++++------------
>> block/bfq-iosched.c | 151 +++++++++++++++++++++++++++++---------------
>> block/bfq-iosched.h | 51 ++++++++++++---
>> 3 files changed, 194 insertions(+), 103 deletions(-)
>>
>> diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
>> index 144bca006463..d243c429d9c0 100644
>> --- a/block/bfq-cgroup.c
>> +++ b/block/bfq-cgroup.c
>> @@ -700,6 +700,48 @@ void bfq_bfqq_move(struct bfq_data *bfqd, struct bfq_queue *bfqq,
>> bfq_put_queue(bfqq);
>> }
>>
>> +static void bfq_sync_bfqq_move(struct bfq_data *bfqd,
>> + struct bfq_queue *sync_bfqq,
>> + struct bfq_io_cq *bic,
>> + struct bfq_group *bfqg,
>> + unsigned int act_idx)
>> +{
>> + if (!sync_bfqq->new_bfqq && !bfq_bfqq_coop(sync_bfqq)) {
>> + /* We are the only user of this bfqq, just move it */
>> + if (sync_bfqq->entity.sched_data != &bfqg->sched_data)
>> + bfq_bfqq_move(bfqd, sync_bfqq, bfqg);
>
> Nit: add a return here to avoid the "else" and save one tab indent level
> for the code below. That will be more pleasant to the eyes :)
>
>> + } else {
>> + struct bfq_queue *bfqq;
>> +
>> + /*
>> + * The queue was merged to a different queue. Check
>> + * that the merge chain still belongs to the same
>> + * cgroup.
>> + */
>> + for (bfqq = sync_bfqq; bfqq; bfqq = bfqq->new_bfqq)
>> + if (bfqq->entity.sched_data !=
>> + &bfqg->sched_data)
>> + break;
>> + if (bfqq) {
>> + /*
>> + * Some queue changed cgroup so the merge is
>> + * not valid anymore. We cannot easily just
>> + * cancel the merge (by clearing new_bfqq) as
>> + * there may be other processes using this
>> + * queue and holding refs to all queues below
>> + * sync_bfqq->new_bfqq. Similarly if the merge
>> + * already happened, we need to detach from
>> + * bfqq now so that we cannot merge bio to a
>> + * request from the old cgroup.
>> + */
>> + bfq_put_cooperator(sync_bfqq);
>> + bfq_release_process_ref(bfqd, sync_bfqq);
>> + bic_set_bfqq(bic, NULL, 1, act_idx);
>> + }
>> + }
>> +}
>> +
>> +
>
> Double blank line.
>
>> /**
>> * __bfq_bic_change_cgroup - move @bic to @bfqg.
>> * @bfqd: the queue descriptor.
>> @@ -714,53 +756,24 @@ static void *__bfq_bic_change_cgroup(struct bfq_data *bfqd,
>> struct bfq_io_cq *bic,
>> struct bfq_group *bfqg)
>> {
>> - struct bfq_queue *async_bfqq = bic_to_bfqq(bic, 0);
>> - struct bfq_queue *sync_bfqq = bic_to_bfqq(bic, 1);
>> struct bfq_entity *entity;
>> + unsigned int act_idx;
>>
>> - if (async_bfqq) {
>> - entity = &async_bfqq->entity;
>> -
>> - if (entity->sched_data != &bfqg->sched_data) {
>> - bic_set_bfqq(bic, NULL, 0);
>> - bfq_release_process_ref(bfqd, async_bfqq);
>> - }
>> - }
>> + for (act_idx = 0; act_idx < bfqd->num_actuators; act_idx++) {
>> + struct bfq_queue *async_bfqq = bic_to_bfqq(bic, 0, act_idx);
>> + struct bfq_queue *sync_bfqq = bic_to_bfqq(bic, 1, act_idx);
>
> The second argument of bic_to_bfqq() is a bool. So it would make more
> sense to use false/true instead of 0/1. That said, creating 2 helpers
> bic_to_async_bfqq() and bic_to_sync_bfqq() without that second argument
> would make the code more readable and less error prone I think.
>
>>
>> - if (sync_bfqq) {
>> - if (!sync_bfqq->new_bfqq && !bfq_bfqq_coop(sync_bfqq)) {
>> - /* We are the only user of this bfqq, just move it */
>> - if (sync_bfqq->entity.sched_data != &bfqg->sched_data)
>> - bfq_bfqq_move(bfqd, sync_bfqq, bfqg);
>> - } else {
>> - struct bfq_queue *bfqq;
>> + if (async_bfqq) {
>> + entity = &async_bfqq->entity;
>>
>> - /*
>> - * The queue was merged to a different queue. Check
>> - * that the merge chain still belongs to the same
>> - * cgroup.
>> - */
>> - for (bfqq = sync_bfqq; bfqq; bfqq = bfqq->new_bfqq)
>> - if (bfqq->entity.sched_data !=
>> - &bfqg->sched_data)
>> - break;
>> - if (bfqq) {
>> - /*
>> - * Some queue changed cgroup so the merge is
>> - * not valid anymore. We cannot easily just
>> - * cancel the merge (by clearing new_bfqq) as
>> - * there may be other processes using this
>> - * queue and holding refs to all queues below
>> - * sync_bfqq->new_bfqq. Similarly if the merge
>> - * already happened, we need to detach from
>> - * bfqq now so that we cannot merge bio to a
>> - * request from the old cgroup.
>> - */
>> - bfq_put_cooperator(sync_bfqq);
>> - bfq_release_process_ref(bfqd, sync_bfqq);
>> - bic_set_bfqq(bic, NULL, 1);
>> + if (entity->sched_data != &bfqg->sched_data) {
>
> You are referencing the entity variable once here only. So is it really
> needed ?
>
>> + bic_set_bfqq(bic, NULL, 0, act_idx);
>> + bfq_release_process_ref(bfqd, async_bfqq);
>> }
>> }
>> +
>> + if (sync_bfqq)
>> + bfq_sync_bfqq_move(bfqd, sync_bfqq, bic, bfqg, act_idx);
>> }
>>
>> return bfqg;
>> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
>> index 7ea427817f7f..5c69394bbb65 100644
>> --- a/block/bfq-iosched.c
>> +++ b/block/bfq-iosched.c
>> @@ -377,14 +377,19 @@ static const unsigned long bfq_late_stable_merging = 600;
>> #define RQ_BIC(rq) ((struct bfq_io_cq *)((rq)->elv.priv[0]))
>> #define RQ_BFQQ(rq) ((rq)->elv.priv[1])
>>
>> -struct bfq_queue *bic_to_bfqq(struct bfq_io_cq *bic, bool is_sync)
>> +struct bfq_queue *bic_to_bfqq(struct bfq_io_cq *bic,
>> + bool is_sync,
>> + unsigned int actuator_idx)
>
> Why the line split for the last argument ?
>
>> {
>> - return bic->bfqq[is_sync];
>> + return bic->bfqq[is_sync][actuator_idx];
>
> See comment above. This is really broken I think. You should not use a
> bool as an array index. Write it as:
>
> if (is_sync)
> return bic->bfqq[1][actuator_idx];
> return bic->bfqq[0][actuator_idx];
>
> Or as suggested, create 2 helpers.
>
>> }
>>
>> static void bfq_put_stable_ref(struct bfq_queue *bfqq);
>>
>> -void bic_set_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq, bool is_sync)
>> +void bic_set_bfqq(struct bfq_io_cq *bic,
>> + struct bfq_queue *bfqq,
>> + bool is_sync,
>> + unsigned int actuator_idx)
>> {
>> /*
>> * If bfqq != NULL, then a non-stable queue merge between
>> @@ -399,7 +404,7 @@ void bic_set_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq, bool is_sync)
>> * we cancel the stable merge if
>> * bic->stable_merge_bfqq == bfqq.
>> */
>> - bic->bfqq[is_sync] = bfqq;
>> + bic->bfqq[is_sync][actuator_idx] = bfqq;
>
> Same comment as above. Using a bool as an index array feels very wrong to
> me. This seems very fragile/dependent on waht the compiler does with bool
> type.
>
>>
>> if (bfqq && bic->stable_merge_bfqq == bfqq) {
>> /*
>> @@ -672,9 +677,9 @@ static void bfq_limit_depth(blk_opf_t opf, struct blk_mq_alloc_data *data)
>> {
>> struct bfq_data *bfqd = data->q->elevator->elevator_data;
>> struct bfq_io_cq *bic = bfq_bic_lookup(data->q);
>> - struct bfq_queue *bfqq = bic ? bic_to_bfqq(bic, op_is_sync(opf)) : NULL;
>
> Given that you are repeating this same pattern many times, the test for
> bic != NULL should go into the bic_to_bfqq() helper.
>
>> int depth;
>> unsigned limit = data->q->nr_requests;
>> + unsigned int act_idx;
>>
>> /* Sync reads have full depth available */
>> if (op_is_sync(opf) && !op_is_write(opf)) {
>> @@ -684,14 +689,21 @@ static void bfq_limit_depth(blk_opf_t opf, struct blk_mq_alloc_data *data)
>> limit = (limit * depth) >> bfqd->full_depth_shift;
>> }
>>
>> - /*
>> - * Does queue (or any parent entity) exceed number of requests that
>> - * should be available to it? Heavily limit depth so that it cannot
>> - * consume more available requests and thus starve other entities.
>> - */
>> - if (bfqq && bfqq_request_over_limit(bfqq, limit))
>> - depth = 1;
>> + for (act_idx = 0; act_idx < bfqd->num_actuators; act_idx++) {
>> + struct bfq_queue *bfqq =
>> + bic ? bic_to_bfqq(bic, op_is_sync(opf), act_idx) : NULL;
>>
>> + /*
>> + * Does queue (or any parent entity) exceed number of
>> + * requests that should be available to it? Heavily
>> + * limit depth so that it cannot consume more
>> + * available requests and thus starve other entities.
>> + */
>> + if (bfqq && bfqq_request_over_limit(bfqq, limit)) {
>> + depth = 1;
>> + break;
>> + }
>> + }
>> bfq_log(bfqd, "[%s] wr_busy %d sync %d depth %u",
>> __func__, bfqd->wr_busy_queues, op_is_sync(opf), depth);
>> if (depth)
>> @@ -2142,7 +2154,7 @@ static void bfq_check_waker(struct bfq_data *bfqd, struct bfq_queue *bfqq,
>> * We reset waker detection logic also if too much time has passed
>> * since the first detection. If wakeups are rare, pointless idling
>> * doesn't hurt throughput that much. The condition below makes sure
>> - * we do not uselessly idle blocking waker in more than 1/64 cases.
>> + * we do not uselessly idle blocking waker in more than 1/64 cases.
>> */
>> if (bfqd->last_completed_rq_bfqq !=
>> bfqq->tentative_waker_bfqq ||
>> @@ -2454,6 +2466,16 @@ static void bfq_remove_request(struct request_queue *q,
>>
>> }
>>
>> +/* get the index of the actuator that will serve bio */
>
> Generally, function comments use the multi-line comment style...
>
> /*
> * Get the index of the actuator that will serve @bio.
> */
>
>> +static unsigned int bfq_actuator_index(struct bfq_data *bfqd, struct bio *bio)
>> +{
>> + /*
>> + * Multi-actuator support not complete yet, so always return 0
>> + * for the moment.
>> + */
>
> Nit: You did comment about this in the commit message. So I do not think
> having this comment here helps.
>
> Note that you could have a prep patch before this patch that gather the
> actuator information for the device, and only does that. So this function
> here could actually have meat instead of being empty. But that may make
> the entire series more complicated, so not a big deal.
>
Yep. The idea here is to exercise multi-actuator functionalities
only after setting up all the needed pieces. And to keep these
functionalities off until they can work correctly, we make
bfq_actuator_index returns 0. Otherwise I should invent a
different way to keep multi-actuary support off. Yet I don't see a
clean alternative.
Apart from this point, I'll apply al your suggestions and send a V7.
Thanks,
Paolo
>> + return 0;
>> +}
>> +
>> static bool bfq_bio_merge(struct request_queue *q, struct bio *bio,
>> unsigned int nr_segs)
>> {
>> @@ -2478,7 +2500,8 @@ static bool bfq_bio_merge(struct request_queue *q, struct bio *bio,
>> */
>> bfq_bic_update_cgroup(bic, bio);
>>
>> - bfqd->bio_bfqq = bic_to_bfqq(bic, op_is_sync(bio->bi_opf));
>> + bfqd->bio_bfqq = bic_to_bfqq(bic, op_is_sync(bio->bi_opf),
>> + bfq_actuator_index(bfqd, bio));
>> } else {
>> bfqd->bio_bfqq = NULL;
>> }
>> @@ -3174,7 +3197,7 @@ bfq_merge_bfqqs(struct bfq_data *bfqd, struct bfq_io_cq *bic,
>> /*
>> * Merge queues (that is, let bic redirect its requests to new_bfqq)
>> */
>> - bic_set_bfqq(bic, new_bfqq, 1);
>> + bic_set_bfqq(bic, new_bfqq, 1, bfqq->actuator_idx);
>> bfq_mark_bfqq_coop(new_bfqq);
>> /*
>> * new_bfqq now belongs to at least two bics (it is a shared queue):
>> @@ -4808,11 +4831,12 @@ static struct bfq_queue *bfq_select_queue(struct bfq_data *bfqd)
>> */
>> if (bfq_bfqq_wait_request(bfqq) ||
>> (bfqq->dispatched != 0 && bfq_better_to_idle(bfqq))) {
>> + unsigned int act_idx = bfqq->actuator_idx;
>> struct bfq_queue *async_bfqq =
>> - bfqq->bic && bfqq->bic->bfqq[0] &&
>> - bfq_bfqq_busy(bfqq->bic->bfqq[0]) &&
>> - bfqq->bic->bfqq[0]->next_rq ?
>> - bfqq->bic->bfqq[0] : NULL;
>> + bfqq->bic && bfqq->bic->bfqq[0][act_idx] &&
>> + bfq_bfqq_busy(bfqq->bic->bfqq[0][act_idx]) &&
>> + bfqq->bic->bfqq[0][act_idx]->next_rq ?
>> + bfqq->bic->bfqq[0][act_idx] : NULL;
>
> Missing a blank line before this hunk, after the declaration. And I
> personally think that this is totally unreadable. Using a plain if/else
> would improve that.
>
>> struct bfq_queue *blocked_bfqq =
>> !hlist_empty(&bfqq->woken_list) ?
>> container_of(bfqq->woken_list.first,
>> @@ -4904,7 +4928,7 @@ static struct bfq_queue *bfq_select_queue(struct bfq_data *bfqd)
>> icq_to_bic(async_bfqq->next_rq->elv.icq) == bfqq->bic &&
>> bfq_serv_to_charge(async_bfqq->next_rq, async_bfqq) <=
>> bfq_bfqq_budget_left(async_bfqq))
>> - bfqq = bfqq->bic->bfqq[0];
>> + bfqq = bfqq->bic->bfqq[0][act_idx];
>> else if (bfqq->waker_bfqq &&
>> bfq_bfqq_busy(bfqq->waker_bfqq) &&
>> bfqq->waker_bfqq->next_rq &&
>> @@ -5365,49 +5389,59 @@ static void bfq_exit_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq)
>> bfq_release_process_ref(bfqd, bfqq);
>> }
>>
>> -static void bfq_exit_icq_bfqq(struct bfq_io_cq *bic, bool is_sync)
>> +static void bfq_exit_icq_bfqq(struct bfq_io_cq *bic,
>> + bool is_sync,
>> + unsigned int actuator_idx)
>
> Why the line split here ?
>
>> {
>> - struct bfq_queue *bfqq = bic_to_bfqq(bic, is_sync);
>> + struct bfq_queue *bfqq = bic_to_bfqq(bic, is_sync, actuator_idx);
>> struct bfq_data *bfqd;
>>
>> if (bfqq)
>> bfqd = bfqq->bfqd; /* NULL if scheduler already exited */
>>
>> if (bfqq && bfqd) {
>> - unsigned long flags;
>> -
>> - spin_lock_irqsave(&bfqd->lock, flags);
>> bfqq->bic = NULL;
>> bfq_exit_bfqq(bfqd, bfqq);
>> - bic_set_bfqq(bic, NULL, is_sync);
>> - spin_unlock_irqrestore(&bfqd->lock, flags);
>> + bic_set_bfqq(bic, NULL, is_sync, actuator_idx);
>> }
>> }
>>
>> static void bfq_exit_icq(struct io_cq *icq)
>> {
>> struct bfq_io_cq *bic = icq_to_bic(icq);
>> + struct bfq_data *bfqd = bic_to_bfqd(bic);
>> + unsigned long flags;
>> + unsigned int act_idx;
>> + unsigned int num_actuators;
>>
>> - if (bic->stable_merge_bfqq) {
>> - struct bfq_data *bfqd = bic->stable_merge_bfqq->bfqd;
>> -
>> + /*
>> + * bfqd is NULL if scheduler already exited, and in that case
>> + * this is the last time these queues are accessed.
>> + */
>> + if (bfqd) {
>> + spin_lock_irqsave(&bfqd->lock, flags);
>> + num_actuators = bfqd->num_actuators;
>> + } else {
>> /*
>> - * bfqd is NULL if scheduler already exited, and in
>> - * that case this is the last time bfqq is accessed.
>> + * bfqd->num_actuators not available any longer, cycle
>> + * over all possible per-actuator bfqqs in next
>> + * loop. We rely on bic being zeroed on creation, and
>> + * therefore on its unused per-actuator fields being
>> + * NULL.
>> */
>> - if (bfqd) {
>> - unsigned long flags;
>> + num_actuators = BFQ_MAX_ACTUATORS;
>> + }
>
> Why not simply initialize num_actuators to BFQ_MAX_ACTUATORS when it is
> declared and drop that "else" above ?
>
>>
>> - spin_lock_irqsave(&bfqd->lock, flags);
>> - bfq_put_stable_ref(bic->stable_merge_bfqq);
>> - spin_unlock_irqrestore(&bfqd->lock, flags);
>> - } else {
>> - bfq_put_stable_ref(bic->stable_merge_bfqq);
>> - }
>> + if (bic->stable_merge_bfqq)
>> + bfq_put_stable_ref(bic->stable_merge_bfqq);
>> +
>> + for (act_idx = 0; act_idx < num_actuators; act_idx++) {
>> + bfq_exit_icq_bfqq(bic, true, act_idx);
>> + bfq_exit_icq_bfqq(bic, false, act_idx);
>> }
>>
>> - bfq_exit_icq_bfqq(bic, true);
>> - bfq_exit_icq_bfqq(bic, false);
>> + if (bfqd)
>> + spin_unlock_irqrestore(&bfqd->lock, flags);
>> }
>>
>> /*
>> @@ -5484,23 +5518,25 @@ static void bfq_check_ioprio_change(struct bfq_io_cq *bic, struct bio *bio)
>>
>> bic->ioprio = ioprio;
>>
>> - bfqq = bic_to_bfqq(bic, false);
>> + bfqq = bic_to_bfqq(bic, false, bfq_actuator_index(bfqd, bio));
>> if (bfqq) {
>> bfq_release_process_ref(bfqd, bfqq);
>> bfqq = bfq_get_queue(bfqd, bio, false, bic, true);
>> - bic_set_bfqq(bic, bfqq, false);
>> + bic_set_bfqq(bic, bfqq, false, bfq_actuator_index(bfqd, bio));
>> }
>>
>> - bfqq = bic_to_bfqq(bic, true);
>> + bfqq = bic_to_bfqq(bic, true, bfq_actuator_index(bfqd, bio));
>> if (bfqq)
>> bfq_set_next_ioprio_data(bfqq, bic);
>> }
>>
>> static void bfq_init_bfqq(struct bfq_data *bfqd, struct bfq_queue *bfqq,
>> - struct bfq_io_cq *bic, pid_t pid, int is_sync)
>> + struct bfq_io_cq *bic, pid_t pid, int is_sync,
>> + unsigned int act_idx)
>> {
>> u64 now_ns = ktime_get_ns();
>>
>> + bfqq->actuator_idx = act_idx;
>> RB_CLEAR_NODE(&bfqq->entity.rb_node);
>> INIT_LIST_HEAD(&bfqq->fifo);
>> INIT_HLIST_NODE(&bfqq->burst_list_node);
>> @@ -5739,6 +5775,7 @@ static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd,
>> struct bfq_group *bfqg;
>>
>> bfqg = bfq_bio_bfqg(bfqd, bio);
>> +
>
> whiteline change.
>
>> if (!is_sync) {
>> async_bfqq = bfq_async_queue_prio(bfqd, bfqg, ioprio_class,
>> ioprio);
>> @@ -5753,7 +5790,7 @@ static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd,
>>
>> if (bfqq) {
>> bfq_init_bfqq(bfqd, bfqq, bic, current->pid,
>> - is_sync);
>> + is_sync, bfq_actuator_index(bfqd, bio));
>> bfq_init_entity(&bfqq->entity, bfqg);
>> bfq_log_bfqq(bfqd, bfqq, "allocated");
>> } else {
>> @@ -6068,7 +6105,8 @@ static bool __bfq_insert_request(struct bfq_data *bfqd, struct request *rq)
>> * then complete the merge and redirect it to
>> * new_bfqq.
>> */
>> - if (bic_to_bfqq(RQ_BIC(rq), 1) == bfqq)
>> + if (bic_to_bfqq(RQ_BIC(rq), 1,
>> + bfq_actuator_index(bfqd, rq->bio)) == bfqq)
>> bfq_merge_bfqqs(bfqd, RQ_BIC(rq),
>> bfqq, new_bfqq);
>>
>> @@ -6622,7 +6660,7 @@ bfq_split_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq)
>> return bfqq;
>> }
>>
>> - bic_set_bfqq(bic, NULL, 1);
>> + bic_set_bfqq(bic, NULL, 1, bfqq->actuator_idx);
>>
>> bfq_put_cooperator(bfqq);
>>
>> @@ -6636,7 +6674,8 @@ static struct bfq_queue *bfq_get_bfqq_handle_split(struct bfq_data *bfqd,
>> bool split, bool is_sync,
>> bool *new_queue)
>> {
>> - struct bfq_queue *bfqq = bic_to_bfqq(bic, is_sync);
>> + unsigned int act_idx = bfq_actuator_index(bfqd, bio);
>> + struct bfq_queue *bfqq = bic_to_bfqq(bic, is_sync, act_idx);
>>
>> if (likely(bfqq && bfqq != &bfqd->oom_bfqq))
>> return bfqq;
>> @@ -6648,7 +6687,7 @@ static struct bfq_queue *bfq_get_bfqq_handle_split(struct bfq_data *bfqd,
>> bfq_put_queue(bfqq);
>> bfqq = bfq_get_queue(bfqd, bio, is_sync, bic, split);
>>
>> - bic_set_bfqq(bic, bfqq, is_sync);
>> + bic_set_bfqq(bic, bfqq, is_sync, act_idx);
>> if (split && is_sync) {
>> if ((bic->was_in_burst_list && bfqd->large_burst) ||
>> bic->saved_in_large_burst)
>> @@ -7090,8 +7129,10 @@ static int bfq_init_queue(struct request_queue *q, struct elevator_type *e)
>> * Our fallback bfqq if bfq_find_alloc_queue() runs into OOM issues.
>> * Grab a permanent reference to it, so that the normal code flow
>> * will not attempt to free it.
>> + * Set zero as actuator index: we will pretend that
>> + * all I/O requests are for the same actuator.
>> */
>> - bfq_init_bfqq(bfqd, &bfqd->oom_bfqq, NULL, 1, 0);
>> + bfq_init_bfqq(bfqd, &bfqd->oom_bfqq, NULL, 1, 0, 0);
>> bfqd->oom_bfqq.ref++;
>> bfqd->oom_bfqq.new_ioprio = BFQ_DEFAULT_QUEUE_IOPRIO;
>> bfqd->oom_bfqq.new_ioprio_class = IOPRIO_CLASS_BE;
>> @@ -7110,6 +7151,12 @@ static int bfq_init_queue(struct request_queue *q, struct elevator_type *e)
>>
>> bfqd->queue = q;
>>
>> + /*
>> + * Multi-actuator support not complete yet, default to single
>> + * actuator for the moment.
>> + */
>> + bfqd->num_actuators = 1;
>
> This should be the default anyway, so is that comment really necessary ?
>
>> +
>> INIT_LIST_HEAD(&bfqd->dispatch);
>>
>> hrtimer_init(&bfqd->idle_slice_timer, CLOCK_MONOTONIC,
>> diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
>> index 71f721670ab6..bfcbd8ea9000 100644
>> --- a/block/bfq-iosched.h
>> +++ b/block/bfq-iosched.h
>> @@ -33,6 +33,14 @@
>> */
>> #define BFQ_SOFTRT_WEIGHT_FACTOR 100
>>
>> +/*
>> + * Maximum number of actuators supported. This constant is used simply
>> + * to define the size of the static array that will contain
>> + * per-actuator data. The current value is hopefully a good upper
>> + * bound to the possible number of actuators of any actual drive.
>> + */
>> +#define BFQ_MAX_ACTUATORS 32
>
> That seems really excessive... What about 4 or 8 ?
>
>> +
>> struct bfq_entity;
>>
>> /**
>> @@ -225,12 +233,14 @@ struct bfq_ttime {
>> * struct bfq_queue - leaf schedulable entity.
>> *
>> * A bfq_queue is a leaf request queue; it can be associated with an
>> - * io_context or more, if it is async or shared between cooperating
>> - * processes. @cgroup holds a reference to the cgroup, to be sure that it
>> - * does not disappear while a bfqq still references it (mostly to avoid
>> - * races between request issuing and task migration followed by cgroup
>> - * destruction).
>> - * All the fields are protected by the queue lock of the containing bfqd.
>> + * io_context or more, if it is async or shared between cooperating
>> + * processes. Besides, it contains I/O requests for only one actuator
>> + * (an io_context is associated with a different bfq_queue for each
>> + * actuator it generates I/O for). @cgroup holds a reference to the
>> + * cgroup, to be sure that it does not disappear while a bfqq still
>> + * references it (mostly to avoid races between request issuing and
>> + * task migration followed by cgroup destruction). All the fields are
>> + * protected by the queue lock of the containing bfqd.
>> */
>> struct bfq_queue {
>> /* reference counter */
>> @@ -395,6 +405,9 @@ struct bfq_queue {
>> * the woken queues when this queue exits.
>> */
>> struct hlist_head woken_list;
>> +
>> + /* index of the actuator this queue is associated with */
>> + unsigned int actuator_idx;
>> };
>>
>> /**
>> @@ -403,8 +416,17 @@ struct bfq_queue {
>> struct bfq_io_cq {
>> /* associated io_cq structure */
>> struct io_cq icq; /* must be the first member */
>> - /* array of two process queues, the sync and the async */
>> - struct bfq_queue *bfqq[2];
>> + /*
>> + * Matrix of associated process queues: first row for async
>> + * queues, second row sync queues. Each row contains one
>> + * column for each actuator. An I/O request generated by the
>> + * process is inserted into the queue pointed by bfqq[i][j] if
>> + * the request is to be served by the j-th actuator of the
>> + * drive, where i==0 or i==1, depending on whether the request
>> + * is async or sync. So there is a distinct queue for each
>> + * actuator.
>> + */
>> + struct bfq_queue *bfqq[2][BFQ_MAX_ACTUATORS];
>> /* per (request_queue, blkcg) ioprio */
>> int ioprio;
>> #ifdef CONFIG_BFQ_GROUP_IOSCHED
>> @@ -768,6 +790,13 @@ struct bfq_data {
>> */
>> unsigned int word_depths[2][2];
>> unsigned int full_depth_shift;
>> +
>> + /*
>> + * Number of independent actuators. This is equal to 1 in
>> + * case of single-actuator drives.
>> + */
>> + unsigned int num_actuators;
>> +
>> };
>>
>> enum bfqq_state_flags {
>> @@ -964,8 +993,10 @@ struct bfq_group {
>>
>> extern const int bfq_timeout;
>>
>> -struct bfq_queue *bic_to_bfqq(struct bfq_io_cq *bic, bool is_sync);
>> -void bic_set_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq, bool is_sync);
>> +struct bfq_queue *bic_to_bfqq(struct bfq_io_cq *bic, bool is_sync,
>> + unsigned int actuator_idx);
>> +void bic_set_bfqq(struct bfq_io_cq *bic, struct bfq_queue *bfqq, bool is_sync,
>> + unsigned int actuator_idx);
>> struct bfq_data *bic_to_bfqd(struct bfq_io_cq *bic);
>> void bfq_pos_tree_add_move(struct bfq_data *bfqd, struct bfq_queue *bfqq);
>> void bfq_weights_tree_add(struct bfq_data *bfqd, struct bfq_queue *bfqq,
>
> --
> Damien Le Moal
> Western Digital Research
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