Re: [PATCH V3 1/8] block, bfq: split sync bfq_queues on a per-actuator basis

[Damien Le Moal]

On 10/12/22 00:45, Paolo VALENTE wrote:
> 
> 
>> Il giorno 5 ott 2022, alle ore 01:04, Damien Le Moal <damien.lemoal@xxxxxxxxxxxxxxxxxx> ha scritto:
>>
>> On 10/4/22 18:40, Paolo Valente wrote:
>>> Multi-actuator drives appear as a single device to the I/O subsystem [1].
>>
>> Not necessarilly. Multi-lun scsi model will show up as multiple drives
>> with one actuator each.
>>
> 
> Right.  In that case, IIUC each LUN appears as a separate device (in
> /dev/), and allows one of the actuators to be controlled separately.
> So each such device has only one range in the air data structure, and
> the extension in these patches is simply inactive.

Yes. My comment was all about not being so general with how multi-actuator
drives are seen from the host. Your sentence should be rephrased to
something like: "Single LUN multi-actuator SCSI drives and all
multi-actuator SATA drives appear as a single device to the I/O subsystem."

No confusion possible this way :)

> 
> That said, I'll try to address all your suggestions for this and the
> other patches, and send a new version of this series.
> 
> Thank you,
> Paolo
> 
>>> 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@xxxxxxxxx>
>>> Signed-off-by: Paolo Valente <paolo.valente@xxxxxxxxxx>
>>> ---
>>> block/bfq-cgroup.c  |  95 +++++++++++++++++--------------
>>> block/bfq-iosched.c | 135 +++++++++++++++++++++++++++-----------------
>>> block/bfq-iosched.h |  38 +++++++++----
>>> 3 files changed, 164 insertions(+), 104 deletions(-)
>>>
>>> diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
>>> index 30b15a9a47c4..a745dd9d658e 100644
>>> --- a/block/bfq-cgroup.c
>>> +++ b/block/bfq-cgroup.c
>>> @@ -705,6 +705,48 @@ 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);
>>> +	} 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);
>>> +		}
>>> +	}
>>> +}
>>> +
>>> +
>>> /**
>>>  * __bfq_bic_change_cgroup - move @bic to @bfqg.
>>>  * @bfqd: the queue descriptor.
>>> @@ -719,53 +761,24 @@ 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 < BFQ_NUM_ACTUATORS; act_idx++) {
>>
>> Why loop over all BFQ_NUM_ACTUATORS actuators even though this patch
>> itself is not enough to support multiple actuators ?
>> You then have patch 5 changing this macro to BFQ_MAX_ACTUATORS and then
>> patch 6 finally introducing a nr_ia_range bfq field to indicate the
>> effective number of actuators.
>>
>> Why not:
>> 1) introduce BFQ_MAX_ACTUATORS in this patch and define the bfqq field
>> using it
>> 2) introduce a nr_actuators field defaultint to 1 for now and use that as
>> the upper bound for actuator earch loop
>>
>> That would be 100% consistent with the current code (no change in
>> practice) and avoid all the code churn you have in the following patches.
>>
>>> +		struct bfq_queue *async_bfqq = bic_to_bfqq(bic, 0, act_idx);
>>> +		struct bfq_queue *sync_bfqq = bic_to_bfqq(bic, 1, act_idx);
>>>
>>> -	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) {
>>> +				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 c740b41fe0a4..c2485b599d87 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)
>>> {
>>> -	return bic->bfqq[is_sync];
>>> +	return bic->bfqq[is_sync][actuator_idx];
>>> }
>>>
>>> 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;
>>>
>>> 	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;
>>> 	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 < BFQ_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 */
>>> +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.
>>> +	 */
>>> +	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;
>>> 		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 &&
>>> @@ -5367,49 +5391,47 @@ 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)
>>> {
>>> -	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;
>>>
>>> -	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 bfqq is accessed.
>>> -		 */
>>> -		if (bfqd) {
>>> -			unsigned long flags;
>>> +	/*
>>> +	 * 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);
>>>
>>> -			spin_lock_irqsave(&bfqd->lock, flags);
>>> -			bfq_put_stable_ref(bic->stable_merge_bfqq);
>>> -			spin_unlock_irqrestore(&bfqd->lock, flags);
>>> -		} else {
>>> +	for (act_idx = 0; act_idx < BFQ_NUM_ACTUATORS; act_idx++) {
>>> +		if (bic->stable_merge_bfqq)
>>> 			bfq_put_stable_ref(bic->stable_merge_bfqq);
>>> -		}
>>> +
>>> +		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);
>>> }
>>>
>>> /*
>>> @@ -5486,23 +5508,25 @@ 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);
>>> @@ -5741,6 +5765,7 @@ static struct bfq_queue *bfq_get_queue(struct bfq_data *bfqd,
>>> 	struct bfq_group *bfqg;
>>>
>>> 	bfqg = bfq_bio_bfqg(bfqd, bio);
>>> +
>>> 	if (!is_sync) {
>>> 		async_bfqq = bfq_async_queue_prio(bfqd, bfqg, ioprio_class,
>>> 						  ioprio);
>>> @@ -5755,7 +5780,7 @@ 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 {
>>> @@ -6070,7 +6095,8 @@ 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);
>>>
>>> @@ -6624,7 +6650,7 @@ 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);
>>>
>>> @@ -6638,7 +6664,8 @@ 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;
>>> @@ -6650,7 +6677,7 @@ 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)
>>> @@ -7092,8 +7119,10 @@ 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;
>>> diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
>>> index ad8e513d7e87..8b5225a9e080 100644
>>> --- a/block/bfq-iosched.h
>>> +++ b/block/bfq-iosched.h
>>> @@ -33,6 +33,8 @@
>>>  */
>>> #define BFQ_SOFTRT_WEIGHT_FACTOR	100
>>>
>>> +#define BFQ_NUM_ACTUATORS 2
>>> +
>>> struct bfq_entity;
>>>
>>> /**
>>> @@ -225,12 +227,14 @@ 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 */
>>> @@ -399,6 +403,9 @@ 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;
>>> };
>>>
>>> /**
>>> @@ -407,8 +414,17 @@ 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_NUM_ACTUATORS];
>>> 	/* per (request_queue, blkcg) ioprio */
>>> 	int ioprio;
>>> #ifdef CONFIG_BFQ_GROUP_IOSCHED
>>> @@ -968,8 +984,10 @@ 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
> 
> 

-- 
Damien Le Moal
Western Digital Research