Re: [PATCH V4 3/8] block, bfq: move io_cq-persistent bfqq data into a dedicated struct

From: Damien Le Moal
Date: Thu Oct 20 2022 - 18:55:25 EST

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In reply to: Paolo Valente: "[PATCH V4 3/8] block, bfq: move io_cq-persistent bfqq data into a dedicated struct"
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On 10/21/22 00:26, Paolo Valente wrote:
> With a multi-actuator drive, a process may get associated with multiple
> bfq_queues: one queue for each of the N actuators. So, the bfq_io_cq
> data structure must be able to accommodate its per-queue persistent
> information for N queues. Currently it stores this information for
> just one queue, in several scalar fields.
>
> This is a preparatory commit for moving to accommodating persistent
> information for N queues. In particular, this commit packs all the
> above scalar fields into a single data structure. Then there is now
> only one fieldi, in bfq_io_cq, that stores all the above information. This
> scalar field will then be turned into an array by a following commit.
>
> Suggested-by: Damien Le Moal <damien.lemoal@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Gianmarco Lusvardi <glusvardi@xxxxxxxxxx>
> Signed-off-by: Giulio Barabino <giuliobarabino99@xxxxxxxxx>
> Signed-off-by: Emiliano Maccaferri <inbox@xxxxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Paolo Valente <paolo.valente@xxxxxxxxxx>
> ---
> block/bfq-iosched.c | 118 +++++++++++++++++++++++---------------------
> block/bfq-iosched.h | 52 +++++++++++--------
> 2 files changed, 94 insertions(+), 76 deletions(-)
>
> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
> index 57de6a6a7f06..d2bd94ea2e95 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->bfqq_data->stable_merge_bfqq == bfqq) {

Nit: instead of dereferencing bic->bfqq_data 3 times in this function,
what about adding a "bfqq_data = bic->bfqq_data" local variable ? That
would make the code more readable.

> /*
> * 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->bfqq_data->stable_merge_bfqq);
>
> - bic->stable_merge_bfqq = NULL;
> + bic->bfqq_data->stable_merge_bfqq = NULL;
> }
> }
>
> @@ -1177,35 +1177,36 @@ 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);
>
> - if (bic->saved_has_short_ttime)
> + if (bic->bfqq_data->saved_has_short_ttime)

Same comment here, but given the number of times you dereference that
pointer in this function, I would consider that comment more than a nit here.

The same comment applies to many of the functions you modify after this hunk.

> bfq_mark_bfqq_has_short_ttime(bfqq);
> else
> bfq_clear_bfqq_has_short_ttime(bfqq);
>
> - if (bic->saved_IO_bound)
> + if (bic->bfqq_data->saved_IO_bound)
> 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->bfqq_data->saved_last_serv_time_ns;
> + bfqq->inject_limit = bic->bfqq_data->saved_inject_limit;
> + bfqq->decrease_time_jif = bic->bfqq_data->saved_decrease_time_jif;
>
> - 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->bfqq_data->saved_weight;
> + bfqq->ttime = bic->bfqq_data->saved_ttime;
> + bfqq->io_start_time = bic->bfqq_data->saved_io_start_time;
> + bfqq->tot_idle_time = bic->bfqq_data->saved_tot_idle_time;
> /*
> * 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->bfqq_data->saved_wr_coeff;
> }
> - 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->bfqq_data->saved_service_from_wr;
> + bfqq->wr_start_at_switch_to_srt =
> + bic->bfqq_data->saved_wr_start_at_switch_to_srt;
> + bfqq->last_wr_start_finish = bic->bfqq_data->saved_last_wr_start_finish;
> + bfqq->wr_cur_max_time = bic->bfqq_data->saved_wr_cur_max_time;
>
> if (bfqq->wr_coeff > 1 && (bfq_bfqq_in_large_burst(bfqq) ||
> time_is_before_jiffies(bfqq->last_wr_start_finish +
> @@ -1878,7 +1879,7 @@ 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)->bfqq_data->stably_merged) &&
> (*interactive || soft_rt)));
>
> /*
> @@ -2923,21 +2924,21 @@ 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->bfqq_data->stable_merge_bfqq &&
> !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->bfqq_data->stable_merge_bfqq;
> 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->bfqq_data->stable_merge_bfqq = NULL;
>
> if (!idling_boosts_thr_without_issues(bfqd, bfqq) &&
> proc_ref > 0) {
> @@ -2946,10 +2947,10 @@ 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->bfqq_data->stably_merged = true;
> if (new_bfqq->bic)
> - new_bfqq->bic->stably_merged =
> - true;
> + new_bfqq->bic->bfqq_data->stably_merged =
> + true;
> }
> return new_bfqq;
> } else
> @@ -3057,18 +3058,21 @@ 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->bfqq_data->saved_last_serv_time_ns = bfqq->last_serv_time_ns;
> + bic->bfqq_data->saved_inject_limit = bfqq->inject_limit;
> + bic->bfqq_data->saved_decrease_time_jif = bfqq->decrease_time_jif;
> +
> + bic->bfqq_data->saved_weight = bfqq->entity.orig_weight;
> + bic->bfqq_data->saved_ttime = bfqq->ttime;
> + bic->bfqq_data->saved_has_short_ttime =
> + bfq_bfqq_has_short_ttime(bfqq);
> + bic->bfqq_data->saved_IO_bound = bfq_bfqq_IO_bound(bfqq);
> + bic->bfqq_data->saved_io_start_time = bfqq->io_start_time;
> + bic->bfqq_data->saved_tot_idle_time = bfqq->tot_idle_time;
> + bic->bfqq_data->saved_in_large_burst = bfq_bfqq_in_large_burst(bfqq);
> + bic->bfqq_data->was_in_burst_list =
> + !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 +3085,21 @@ 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->bfqq_data->saved_wr_coeff = bfqq->bfqd->bfq_wr_coeff;
> + bic->bfqq_data->saved_wr_start_at_switch_to_srt =
> + bfq_smallest_from_now();
> + bic->bfqq_data->saved_wr_cur_max_time =
> + bfq_wr_duration(bfqq->bfqd);
> + bic->bfqq_data->saved_last_wr_start_finish = jiffies;
> } else {
> - bic->saved_wr_coeff = bfqq->wr_coeff;
> - bic->saved_wr_start_at_switch_to_srt =
> + bic->bfqq_data->saved_wr_coeff = bfqq->wr_coeff;
> + bic->bfqq_data->saved_wr_start_at_switch_to_srt =
> 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->bfqq_data->saved_service_from_wr =
> + bfqq->service_from_wr;
> + bic->bfqq_data->saved_last_wr_start_finish =
> + bfqq->last_wr_start_finish;
> + bic->bfqq_data->saved_wr_cur_max_time = bfqq->wr_cur_max_time;
> }
> }
>
> @@ -5421,8 +5429,8 @@ static void bfq_exit_icq(struct io_cq *icq)
> spin_lock_irqsave(&bfqd->lock, flags);
>
> for (act_idx = 0; act_idx < bfqd->num_actuators; act_idx++) {
> - if (bic->stable_merge_bfqq)
> - bfq_put_stable_ref(bic->stable_merge_bfqq);
> + if (bic->bfqq_data->stable_merge_bfqq)
> + bfq_put_stable_ref(bic->bfqq_data->stable_merge_bfqq);
>
> bfq_exit_icq_bfqq(bic, true, act_idx);
> bfq_exit_icq_bfqq(bic, false, act_idx);
> @@ -5617,8 +5625,8 @@ 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->bfqq_data->stably_merged = true;
> + bic->bfqq_data->stably_merged = true;
>
> /*
> * Reusing merge functions. This implies that
> @@ -5748,7 +5756,7 @@ 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->bfqq_data->stable_merge_bfqq = last_bfqq_created;
> }
> }
>
> @@ -6682,12 +6690,12 @@ 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->bfqq_data->was_in_burst_list && bfqd->large_burst) ||
> + bic->bfqq_data->saved_in_large_burst)
> bfq_mark_bfqq_in_large_burst(bfqq);
> else {
> bfq_clear_bfqq_in_large_burst(bfqq);
> - if (bic->was_in_burst_list)
> + if (bic->bfqq_data->was_in_burst_list)
> /*
> * If bfqq was in the current
> * burst list before being
> @@ -6802,12 +6810,12 @@ 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->bfqq_data->stably_merged) {
> 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->bfqq_data->saved_in_large_burst = true;
>
> bfqq = bfq_split_bfqq(bic, bfqq);
> split = true;
> diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
> index d98e31be447f..6bc7bed97956 100644
> --- a/block/bfq-iosched.h
> +++ b/block/bfq-iosched.h
> @@ -415,27 +415,9 @@ struct bfq_queue {
> };
>
> /**
> - * struct bfq_io_cq - per (request_queue, io_context) structure.
> - */
> -struct bfq_io_cq {
> - /* associated io_cq structure */
> - struct io_cq icq; /* must be the first member */
> - /*
> - * 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
> - uint64_t blkcg_serial_nr; /* the current blkcg serial */
> -#endif
> +* struct bfq_data - bfqq data unique and persistent for associated bfq_io_cq
> +*/
> +struct bfq_iocq_bfqq_data {
> /*
> * Snapshot of the has_short_time flag before merging; taken
> * to remember its value while the queue is merged, so as to
> @@ -490,6 +472,34 @@ struct bfq_io_cq {
> struct bfq_queue *stable_merge_bfqq;
>
> bool stably_merged; /* non splittable if true */
> +};
> +
> +/**
> + * struct bfq_io_cq - per (request_queue, io_context) structure.
> + */
> +struct bfq_io_cq {
> + /* associated io_cq structure */
> + struct io_cq icq; /* must be the first member */
> + /*
> + * 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
> + uint64_t blkcg_serial_nr; /* the current blkcg serial */
> +#endif
> +
> + /* persistent data for associated synchronous process queue */
> + struct bfq_iocq_bfqq_data *bfqq_data;
> +
> unsigned int requests; /* Number of requests this process has in flight */
> };
>

--
Damien Le Moal
Western Digital Research

Next message: Kees Cook: "Re: [PATCH v2 27/39] x86/cet/shstk: Handle signals for shadow stack"
Previous message: Russell King (Oracle): "Re: [RFC PATCH 0/2] Switch ARM to generic find_bit() API"
In reply to: Paolo Valente: "[PATCH V4 3/8] block, bfq: move io_cq-persistent bfqq data into a dedicated struct"
Next in thread: Paolo Valente: "[PATCH V4 6/8] block, bfq: retrieve independent access ranges from request queue"
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