[PATCH V3 3/8] block, bfq: turn scalar fields into arrays in bfq_io_cq

From: Paolo Valente
Date: Tue Oct 04 2022 - 05:43:41 EST

When a bfq_queue Q is merged with another queue, several pieces of
information are saved about Q. These pieces are stored in the
bfq_io_cq data structure of the process associated with Q. In
particular, each such piece is represented by a scalar field in
bfq_io_cq.

Yet, with a multi-actuator drive, a process gets associated with
multiple bfq_queues: one queue for each of the N actuators. Each of
these queues may undergo a merge. So, the bfq_io_cq data structure
must be able to accommodate the above information for N queues.

This commit solves this problem by turning each scalar field into an
array of N elements (and by changing code so as to handle these
arrays).

This solution is written under the assumption that bfq_queues
associated with different actuators cannot be cross-merged. This
assumption holds naturally with basic queue merging: the latter is
triggered by spatial locality, and sectors for different actuators are
not close to each other. As for stable cross-merging, the assumption
here is that it is disabled.

Signed-off-by: Gabriele Felici <felicigb@xxxxxxxxx>
Signed-off-by: Paolo Valente <paolo.valente@xxxxxxxxxx>
---
block/bfq-iosched.c | 139 ++++++++++++++++++++++++--------------------
block/bfq-iosched.h | 52 ++++++++++-------
2 files changed, 105 insertions(+), 86 deletions(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 2a75009c1c06..dede0e948836 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -406,7 +406,7 @@ void bic_set_bfqq(struct bfq_io_cq *bic,
*/
bic->bfqq[is_sync][actuator_idx] = bfqq;

- if (bfqq && bic->stable_merge_bfqq == bfqq) {
+ if (bfqq && bic->stable_merge_bfqq[actuator_idx] == bfqq) {
/*
* Actually, these same instructions are executed also
* in bfq_setup_cooperator, in case of abort or actual
@@ -415,9 +415,9 @@ void bic_set_bfqq(struct bfq_io_cq *bic,
* did so, we would nest even more complexity in this
* function.
*/
- bfq_put_stable_ref(bic->stable_merge_bfqq);
+ bfq_put_stable_ref(bic->stable_merge_bfqq[actuator_idx]);

- bic->stable_merge_bfqq = NULL;
+ bic->stable_merge_bfqq[actuator_idx] = NULL;
}
}

@@ -1176,36 +1176,38 @@ bfq_bfqq_resume_state(struct bfq_queue *bfqq, struct bfq_data *bfqd,
{
unsigned int old_wr_coeff = 1;
bool busy = bfq_already_existing && bfq_bfqq_busy(bfqq);
+ unsigned int a_idx = bfqq->actuator_idx;

- if (bic->saved_has_short_ttime)
+ if (bic->saved_has_short_ttime[a_idx])
bfq_mark_bfqq_has_short_ttime(bfqq);
else
bfq_clear_bfqq_has_short_ttime(bfqq);

- if (bic->saved_IO_bound)
+ if (bic->saved_IO_bound[a_idx])
bfq_mark_bfqq_IO_bound(bfqq);
else
bfq_clear_bfqq_IO_bound(bfqq);

- bfqq->last_serv_time_ns = bic->saved_last_serv_time_ns;
- bfqq->inject_limit = bic->saved_inject_limit;
- bfqq->decrease_time_jif = bic->saved_decrease_time_jif;
+ bfqq->last_serv_time_ns = bic->saved_last_serv_time_ns[a_idx];
+ bfqq->inject_limit = bic->saved_inject_limit[a_idx];
+ bfqq->decrease_time_jif = bic->saved_decrease_time_jif[a_idx];

- bfqq->entity.new_weight = bic->saved_weight;
- bfqq->ttime = bic->saved_ttime;
- bfqq->io_start_time = bic->saved_io_start_time;
- bfqq->tot_idle_time = bic->saved_tot_idle_time;
+ bfqq->entity.new_weight = bic->saved_weight[a_idx];
+ bfqq->ttime = bic->saved_ttime[a_idx];
+ bfqq->io_start_time = bic->saved_io_start_time[a_idx];
+ bfqq->tot_idle_time = bic->saved_tot_idle_time[a_idx];
/*
* Restore weight coefficient only if low_latency is on
*/
if (bfqd->low_latency) {
old_wr_coeff = bfqq->wr_coeff;
- bfqq->wr_coeff = bic->saved_wr_coeff;
+ bfqq->wr_coeff = bic->saved_wr_coeff[a_idx];
}
- bfqq->service_from_wr = bic->saved_service_from_wr;
- bfqq->wr_start_at_switch_to_srt = bic->saved_wr_start_at_switch_to_srt;
- bfqq->last_wr_start_finish = bic->saved_last_wr_start_finish;
- bfqq->wr_cur_max_time = bic->saved_wr_cur_max_time;
+ bfqq->service_from_wr = bic->saved_service_from_wr[a_idx];
+ bfqq->wr_start_at_switch_to_srt =
+ bic->saved_wr_start_at_switch_to_srt[a_idx];
+ bfqq->last_wr_start_finish = bic->saved_last_wr_start_finish[a_idx];
+ bfqq->wr_cur_max_time = bic->saved_wr_cur_max_time[a_idx];

if (bfqq->wr_coeff > 1 && (bfq_bfqq_in_large_burst(bfqq) ||
time_is_before_jiffies(bfqq->last_wr_start_finish +
@@ -1824,6 +1826,16 @@ static bool bfq_bfqq_higher_class_or_weight(struct bfq_queue *bfqq,
return bfqq_weight > in_serv_weight;
}

+/* 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_better_to_idle(struct bfq_queue *bfqq);

static void bfq_bfqq_handle_idle_busy_switch(struct bfq_data *bfqd,
@@ -1878,7 +1890,9 @@ static void bfq_bfqq_handle_idle_busy_switch(struct bfq_data *bfqd,
wr_or_deserves_wr = bfqd->low_latency &&
(bfqq->wr_coeff > 1 ||
(bfq_bfqq_sync(bfqq) &&
- (bfqq->bic || RQ_BIC(rq)->stably_merged) &&
+ (bfqq->bic ||
+ RQ_BIC(rq)->stably_merged
+ [bfq_actuator_index(bfqd, rq->bio)]) &&
(*interactive || soft_rt)));

/*
@@ -2466,16 +2480,6 @@ 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)
{
@@ -2902,6 +2906,7 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
void *io_struct, bool request, struct bfq_io_cq *bic)
{
struct bfq_queue *in_service_bfqq, *new_bfqq;
+ unsigned int a_idx = bfqq->actuator_idx;

/* if a merge has already been setup, then proceed with that first */
if (bfqq->new_bfqq)
@@ -2923,21 +2928,21 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
* stable merging) also if bic is associated with a
* sync queue, but this bfqq is async
*/
- if (bfq_bfqq_sync(bfqq) && bic->stable_merge_bfqq &&
+ if (bfq_bfqq_sync(bfqq) && bic->stable_merge_bfqq[a_idx] &&
!bfq_bfqq_just_created(bfqq) &&
time_is_before_jiffies(bfqq->split_time +
msecs_to_jiffies(bfq_late_stable_merging)) &&
time_is_before_jiffies(bfqq->creation_time +
msecs_to_jiffies(bfq_late_stable_merging))) {
struct bfq_queue *stable_merge_bfqq =
- bic->stable_merge_bfqq;
+ bic->stable_merge_bfqq[a_idx];
int proc_ref = min(bfqq_process_refs(bfqq),
bfqq_process_refs(stable_merge_bfqq));

/* deschedule stable merge, because done or aborted here */
bfq_put_stable_ref(stable_merge_bfqq);

- bic->stable_merge_bfqq = NULL;
+ bic->stable_merge_bfqq[a_idx] = NULL;

if (!idling_boosts_thr_without_issues(bfqd, bfqq) &&
proc_ref > 0) {
@@ -2946,9 +2951,10 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
bfq_setup_merge(bfqq, stable_merge_bfqq);

if (new_bfqq) {
- bic->stably_merged = true;
+ bic->stably_merged[a_idx] = true;
if (new_bfqq->bic)
- new_bfqq->bic->stably_merged =
+ new_bfqq->bic->stably_merged
+ [new_bfqq->actuator_idx] =
true;
}
return new_bfqq;
@@ -3048,6 +3054,8 @@ bfq_setup_cooperator(struct bfq_data *bfqd, struct bfq_queue *bfqq,
static void bfq_bfqq_save_state(struct bfq_queue *bfqq)
{
struct bfq_io_cq *bic = bfqq->bic;
+ /* State must be saved for the right queue index. */
+ unsigned int a_idx = bfqq->actuator_idx;

/*
* If !bfqq->bic, the queue is already shared or its requests
@@ -3057,18 +3065,18 @@ static void bfq_bfqq_save_state(struct bfq_queue *bfqq)
if (!bic)
return;

- bic->saved_last_serv_time_ns = bfqq->last_serv_time_ns;
- bic->saved_inject_limit = bfqq->inject_limit;
- bic->saved_decrease_time_jif = bfqq->decrease_time_jif;
-
- bic->saved_weight = bfqq->entity.orig_weight;
- bic->saved_ttime = bfqq->ttime;
- bic->saved_has_short_ttime = bfq_bfqq_has_short_ttime(bfqq);
- bic->saved_IO_bound = bfq_bfqq_IO_bound(bfqq);
- bic->saved_io_start_time = bfqq->io_start_time;
- bic->saved_tot_idle_time = bfqq->tot_idle_time;
- bic->saved_in_large_burst = bfq_bfqq_in_large_burst(bfqq);
- bic->was_in_burst_list = !hlist_unhashed(&bfqq->burst_list_node);
+ bic->saved_last_serv_time_ns[a_idx] = bfqq->last_serv_time_ns;
+ bic->saved_inject_limit[a_idx] = bfqq->inject_limit;
+ bic->saved_decrease_time_jif[a_idx] = bfqq->decrease_time_jif;
+
+ bic->saved_weight[a_idx] = bfqq->entity.orig_weight;
+ bic->saved_ttime[a_idx] = bfqq->ttime;
+ bic->saved_has_short_ttime[a_idx] = bfq_bfqq_has_short_ttime(bfqq);
+ bic->saved_IO_bound[a_idx] = bfq_bfqq_IO_bound(bfqq);
+ bic->saved_io_start_time[a_idx] = bfqq->io_start_time;
+ bic->saved_tot_idle_time[a_idx] = bfqq->tot_idle_time;
+ bic->saved_in_large_burst[a_idx] = bfq_bfqq_in_large_burst(bfqq);
+ bic->was_in_burst_list[a_idx] = !hlist_unhashed(&bfqq->burst_list_node);
if (unlikely(bfq_bfqq_just_created(bfqq) &&
!bfq_bfqq_in_large_burst(bfqq) &&
bfqq->bfqd->low_latency)) {
@@ -3081,17 +3089,17 @@ static void bfq_bfqq_save_state(struct bfq_queue *bfqq)
* to bfqq, so that to avoid that bfqq unjustly fails
* to enjoy weight raising if split soon.
*/
- bic->saved_wr_coeff = bfqq->bfqd->bfq_wr_coeff;
- bic->saved_wr_start_at_switch_to_srt = bfq_smallest_from_now();
- bic->saved_wr_cur_max_time = bfq_wr_duration(bfqq->bfqd);
- bic->saved_last_wr_start_finish = jiffies;
+ bic->saved_wr_coeff[a_idx] = bfqq->bfqd->bfq_wr_coeff;
+ bic->saved_wr_start_at_switch_to_srt[a_idx] = bfq_smallest_from_now();
+ bic->saved_wr_cur_max_time[a_idx] = bfq_wr_duration(bfqq->bfqd);
+ bic->saved_last_wr_start_finish[a_idx] = jiffies;
} else {
- bic->saved_wr_coeff = bfqq->wr_coeff;
- bic->saved_wr_start_at_switch_to_srt =
+ bic->saved_wr_coeff[a_idx] = bfqq->wr_coeff;
+ bic->saved_wr_start_at_switch_to_srt[a_idx] =
bfqq->wr_start_at_switch_to_srt;
- bic->saved_service_from_wr = bfqq->service_from_wr;
- bic->saved_last_wr_start_finish = bfqq->last_wr_start_finish;
- bic->saved_wr_cur_max_time = bfqq->wr_cur_max_time;
+ bic->saved_service_from_wr[a_idx] = bfqq->service_from_wr;
+ bic->saved_last_wr_start_finish[a_idx] = bfqq->last_wr_start_finish;
+ bic->saved_wr_cur_max_time[a_idx] = bfqq->wr_cur_max_time;
}
}

@@ -5423,8 +5431,8 @@ static void bfq_exit_icq(struct io_cq *icq)
spin_lock_irqsave(&bfqd->lock, flags);

for (act_idx = 0; act_idx < BFQ_NUM_ACTUATORS; act_idx++) {
- if (bic->stable_merge_bfqq)
- bfq_put_stable_ref(bic->stable_merge_bfqq);
+ if (bic->stable_merge_bfqq[act_idx])
+ bfq_put_stable_ref(bic->stable_merge_bfqq[act_idx]);

bfq_exit_icq_bfqq(bic, true, act_idx);
bfq_exit_icq_bfqq(bic, false, act_idx);
@@ -5612,6 +5620,7 @@ bfq_do_early_stable_merge(struct bfq_data *bfqd, struct bfq_queue *bfqq,
struct bfq_io_cq *bic,
struct bfq_queue *last_bfqq_created)
{
+ unsigned int a_idx = last_bfqq_created->actuator_idx;
struct bfq_queue *new_bfqq =
bfq_setup_merge(bfqq, last_bfqq_created);

@@ -5619,8 +5628,8 @@ bfq_do_early_stable_merge(struct bfq_data *bfqd, struct bfq_queue *bfqq,
return bfqq;

if (new_bfqq->bic)
- new_bfqq->bic->stably_merged = true;
- bic->stably_merged = true;
+ new_bfqq->bic->stably_merged[a_idx] = true;
+ bic->stably_merged[a_idx] = true;

/*
* Reusing merge functions. This implies that
@@ -5750,7 +5759,8 @@ static struct bfq_queue *bfq_do_or_sched_stable_merge(struct bfq_data *bfqd,
/*
* Record the bfqq to merge to.
*/
- bic->stable_merge_bfqq = last_bfqq_created;
+ bic->stable_merge_bfqq[last_bfqq_created->actuator_idx]
+ = last_bfqq_created;
}
}

@@ -6684,12 +6694,12 @@ static struct bfq_queue *bfq_get_bfqq_handle_split(struct bfq_data *bfqd,

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)
+ if ((bic->was_in_burst_list[act_idx] && bfqd->large_burst) ||
+ bic->saved_in_large_burst[act_idx])
bfq_mark_bfqq_in_large_burst(bfqq);
else {
bfq_clear_bfqq_in_large_burst(bfqq);
- if (bic->was_in_burst_list)
+ if (bic->was_in_burst_list[act_idx])
/*
* If bfqq was in the current
* burst list before being
@@ -6778,6 +6788,7 @@ static struct bfq_queue *bfq_init_rq(struct request *rq)
struct bfq_queue *bfqq;
bool new_queue = false;
bool bfqq_already_existing = false, split = false;
+ unsigned int a_idx = bfq_actuator_index(bfqd, bio);

if (unlikely(!rq->elv.icq))
return NULL;
@@ -6804,12 +6815,12 @@ static struct bfq_queue *bfq_init_rq(struct request *rq)
if (likely(!new_queue)) {
/* If the queue was seeky for too long, break it apart. */
if (bfq_bfqq_coop(bfqq) && bfq_bfqq_split_coop(bfqq) &&
- !bic->stably_merged) {
+ !bic->stably_merged[a_idx]) {
struct bfq_queue *old_bfqq = bfqq;

/* Update bic before losing reference to bfqq */
if (bfq_bfqq_in_large_burst(bfqq))
- bic->saved_in_large_burst = true;
+ bic->saved_in_large_burst[a_idx] = true;

bfqq = bfq_split_bfqq(bic, bfqq);
split = true;
diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
index 8b5225a9e080..0ff6be18f72a 100644
--- a/block/bfq-iosched.h
+++ b/block/bfq-iosched.h
@@ -431,30 +431,37 @@ struct bfq_io_cq {
uint64_t blkcg_serial_nr; /* the current blkcg serial */
#endif
/*
- * Snapshot of the has_short_time flag before merging; taken
- * to remember its value while the queue is merged, so as to
- * be able to restore it in case of split.
+ * Several fields follow, which are used to support
+ * queue-merging operations. Each field is an array, because a
+ * process may be associated with multiple bfq_queues (see the
+ * field bfqq above). And each of these queues may undergo a
+ * merge.
*/
- bool saved_has_short_ttime;
+ /*
+ * Snapshot of the has_short_time flags before merging; taken
+ * to remember their values while a queue is merged, so as to
+ * be able to restore them in case of split.
+ */
+ bool saved_has_short_ttime[BFQ_NUM_ACTUATORS];
/*
* Same purpose as the previous two fields for the I/O bound
* classification of a queue.
*/
- bool saved_IO_bound;
+ bool saved_IO_bound[BFQ_NUM_ACTUATORS];

- u64 saved_io_start_time;
- u64 saved_tot_idle_time;
+ u64 saved_io_start_time[BFQ_NUM_ACTUATORS];
+ u64 saved_tot_idle_time[BFQ_NUM_ACTUATORS];

/*
- * Same purpose as the previous fields for the value of the
+ * Same purpose as the previous fields for the values of the
* field keeping the queue's belonging to a large burst
*/
- bool saved_in_large_burst;
+ bool saved_in_large_burst[BFQ_NUM_ACTUATORS];
/*
* True if the queue belonged to a burst list before its merge
* with another cooperating queue.
*/
- bool was_in_burst_list;
+ bool was_in_burst_list[BFQ_NUM_ACTUATORS];

/*
* Save the weight when a merge occurs, to be able
@@ -463,27 +470,28 @@ struct bfq_io_cq {
* then the weight of the recycled queue could differ
* from the weight of the original queue.
*/
- unsigned int saved_weight;
+ unsigned int saved_weight[BFQ_NUM_ACTUATORS];

/*
* Similar to previous fields: save wr information.
*/
- unsigned long saved_wr_coeff;
- unsigned long saved_last_wr_start_finish;
- unsigned long saved_service_from_wr;
- unsigned long saved_wr_start_at_switch_to_srt;
- unsigned int saved_wr_cur_max_time;
- struct bfq_ttime saved_ttime;
+ unsigned long saved_wr_coeff[BFQ_NUM_ACTUATORS];
+ unsigned long saved_last_wr_start_finish[BFQ_NUM_ACTUATORS];
+ unsigned long saved_service_from_wr[BFQ_NUM_ACTUATORS];
+ unsigned long saved_wr_start_at_switch_to_srt[BFQ_NUM_ACTUATORS];
+ unsigned int saved_wr_cur_max_time[BFQ_NUM_ACTUATORS];
+ struct bfq_ttime saved_ttime[BFQ_NUM_ACTUATORS];

/* Save also injection state */
- u64 saved_last_serv_time_ns;
- unsigned int saved_inject_limit;
- unsigned long saved_decrease_time_jif;
+ u64 saved_last_serv_time_ns[BFQ_NUM_ACTUATORS];
+ unsigned int saved_inject_limit[BFQ_NUM_ACTUATORS];
+ unsigned long saved_decrease_time_jif[BFQ_NUM_ACTUATORS];

/* candidate queue for a stable merge (due to close creation time) */
- struct bfq_queue *stable_merge_bfqq;
+ struct bfq_queue *stable_merge_bfqq[BFQ_NUM_ACTUATORS];
+
+ bool stably_merged[BFQ_NUM_ACTUATORS]; /* non splittable if true */

- bool stably_merged; /* non splittable if true */
unsigned int requests; /* Number of requests this process has in flight */
};

--
2.20.1