linux-kernel - Re: [PATCH V6 6/8] block, bfq: retrieve independent access ranges from request queue

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Message-ID: <5d062001-2fff-35e5-d951-a61b510727d9@opensource.wdc.com>
Date:   Mon, 21 Nov 2022 10:01:08 +0900
From:   Damien Le Moal <damien.lemoal@...nsource.wdc.com>
To:     Paolo Valente <paolo.valente@...aro.org>,
        Jens Axboe <axboe@...nel.dk>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        arie.vanderhoeven@...gate.com, rory.c.chen@...gate.com,
        Federico Gavioli <f.gavioli97@...il.com>
Subject: Re: [PATCH V6 6/8] block, bfq: retrieve independent access ranges
 from request queue

On 11/4/22 01:26, Paolo Valente wrote:
> From: Federico Gavioli <f.gavioli97@...il.com>
> 
> This patch implements the code to gather the content of the
> independent_access_ranges structure from the request_queue and copy
> it into the queue's bfq_data. This copy is done at queue initialization.
> 
> We copy the access ranges into the bfq_data to avoid taking the queue
> lock each time we access the ranges.
> 
> This implementation, however, puts a limit to the maximum independent
> ranges supported by the scheduler. Such a limit is equal to the constant
> BFQ_MAX_ACTUATORS. This limit was placed to avoid the allocation of
> dynamic memory.
> 
> Co-developed-by: Rory Chen <rory.c.chen@...gate.com>
> Signed-off-by: Rory Chen <rory.c.chen@...gate.com>
> Signed-off-by: Federico Gavioli <f.gavioli97@...il.com>
> Signed-off-by: Paolo Valente <paolo.valente@...aro.org>
> ---
>  block/bfq-iosched.c | 54 ++++++++++++++++++++++++++++++++++++++-------
>  block/bfq-iosched.h |  5 +++++
>  2 files changed, 51 insertions(+), 8 deletions(-)
> 
> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
> index c94b80e3f685..106c8820cc5c 100644
> --- a/block/bfq-iosched.c
> +++ b/block/bfq-iosched.c
> @@ -1831,10 +1831,26 @@ static bool bfq_bfqq_higher_class_or_weight(struct bfq_queue *bfqq,
>  /* 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.
> -	 */
> +	struct blk_independent_access_range *iar;
> +	unsigned int i;
> +	sector_t end;
> +
> +	/* no search needed if one or zero ranges present */
> +	if (bfqd->num_actuators < 2)
> +		return 0;
> +
> +	/* bio_end_sector(bio) gives the sector after the last one */
> +	end = bio_end_sector(bio) - 1;
> +
> +	for (i = 0; i < bfqd->num_actuators; i++) {
> +		iar = &(bfqd->ia_ranges[i]);
> +		if (end >= iar->sector && end < iar->sector + iar->nr_sectors)
> +			return i;
> +	}
> +
> +	WARN_ONCE(true,
> +		  "bfq_actuator_index: bio sector out of ranges: end=%llu\n",
> +		  end);
>  	return 0;
>  }
>  
> @@ -2479,7 +2495,6 @@ static void bfq_remove_request(struct request_queue *q,
>  
>  	if (rq->cmd_flags & REQ_META)
>  		bfqq->meta_pending--;
> -

whiteline change

>  }
>  
>  static bool bfq_bio_merge(struct request_queue *q, struct bio *bio,
> @@ -7144,6 +7159,8 @@ static int bfq_init_queue(struct request_queue *q, struct elevator_type *e)
>  {
>  	struct bfq_data *bfqd;
>  	struct elevator_queue *eq;
> +	unsigned int i;
> +	struct blk_independent_access_ranges *ia_ranges = q->disk->ia_ranges;
>  
>  	eq = elevator_alloc(q, e);
>  	if (!eq)
> @@ -7187,10 +7204,31 @@ 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.
> +	 * If the disk supports multiple actuators, we copy the independent
> +	 * access ranges from the request queue structure.
>  	 */
> -	bfqd->num_actuators = 1;
> +	spin_lock_irq(&q->queue_lock);
> +	if (ia_ranges) {
> +		/*
> +		 * Check if the disk ia_ranges size exceeds the current bfq
> +		 * actuator limit.
> +		 */
> +		if (ia_ranges->nr_ia_ranges > BFQ_MAX_ACTUATORS) {
> +			pr_crit("nr_ia_ranges higher than act limit: iars=%d, max=%d.\n",
> +				ia_ranges->nr_ia_ranges, BFQ_MAX_ACTUATORS);
> +			pr_crit("Falling back to single actuator mode.\n");
> +			bfqd->num_actuators = 0;
> +		} else {
> +			bfqd->num_actuators = ia_ranges->nr_ia_ranges;
> +
> +			for (i = 0; i < bfqd->num_actuators; i++)
> +				bfqd->ia_ranges[i] = ia_ranges->ia_range[i];
> +		}
> +	} else {
> +		bfqd->num_actuators = 0;

That is very weird. The default should be 1 actuator.
ia_ranges->nr_ia_ranges is 0 when the disk does not provide any range
information, meaning it is a regular disk with a single actuator.

> +	}
> +
> +	spin_unlock_irq(&q->queue_lock);
>  
>  	INIT_LIST_HEAD(&bfqd->dispatch);
>  
> diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
> index f1c2e77cbf9a..90130a893c8f 100644
> --- a/block/bfq-iosched.h
> +++ b/block/bfq-iosched.h
> @@ -811,6 +811,11 @@ struct bfq_data {
>  	 */
>  	unsigned int num_actuators;
>  
> +	/*
> +	 * Disk independent access ranges for each actuator
> +	 * in this device.
> +	 */
> +	struct blk_independent_access_range ia_ranges[BFQ_MAX_ACTUATORS];

I fail to see how keeping this information is useful, especially given
that this struct contains a kobj. Why not just copy the sector &
nr_sectors fields into struct bfq_queue ? That would also work for the
single actuator case as then sector will be 0 and nr_sectors will be the
disk total capacity.

I think this patch should be first in the series. That will avoid having
the empty bfq_actuator_index() function.

>  };
>  
>  enum bfqq_state_flags {

-- 
Damien Le Moal
Western Digital Research