Re: [PATCH V9 6/8] block, bfq: retrieve independent access ranges from request queue

[Damien Le Moal]

On 12/8/22 19:43, Paolo Valente wrote:
> From: Federico Gavioli <f.gavioli97@xxxxxxxxx>
> 
> 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@xxxxxxxxxxx>
> Signed-off-by: Rory Chen <rory.c.chen@xxxxxxxxxxx>
> Signed-off-by: Federico Gavioli <f.gavioli97@xxxxxxxxx>
> Signed-off-by: Paolo Valente <paolo.valente@xxxxxxxxxx>
> ---
>  block/bfq-iosched.c | 60 +++++++++++++++++++++++++++++++++++++++------
>  block/bfq-iosched.h |  8 +++++-
>  2 files changed, 59 insertions(+), 9 deletions(-)
> 
> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
> index dcecba3c6e23..957ce61faaf2 100644
> --- a/block/bfq-iosched.c
> +++ b/block/bfq-iosched.c
> @@ -1839,10 +1839,25 @@ static bool bfq_bfqq_higher_class_or_weight(struct bfq_queue *bfqq,
>   */
>  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 (to keep incomplete mechanisms off).
> -	 */
> +	unsigned int i;
> +	sector_t end;
> +
> +	/* no search needed if one or zero ranges present */
> +	if (bfqd->num_actuators == 1)
> +		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++) {
> +		if (end >= bfqd->sector[i] &&
> +		    end < bfqd->sector[i] + bfqd->nr_sectors[i])
> +			return i;
> +	}
> +
> +	WARN_ONCE(true,
> +		  "bfq_actuator_index: bio sector out of ranges: end=%llu\n",
> +		  end);
>  	return 0;
>  }
>  
> @@ -7160,6 +7175,8 @@ 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)
> @@ -7202,12 +7219,39 @@ static int bfq_init_queue(struct request_queue *q, struct elevator_type *e)
>  
>  	bfqd->queue = q;
>  
> +	bfqd->num_actuators = 1;
>  	/*
> -	 * Multi-actuator support not complete yet, unconditionally
> -	 * set to only one actuator for the moment (to keep incomplete
> -	 * mechanisms off).
> +	 * If the disk supports multiple actuators, copy 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");
> +		} else {
> +			bfqd->num_actuators = ia_ranges->nr_ia_ranges;
> +
> +			for (i = 0; i < bfqd->num_actuators; i++) {
> +				bfqd->sector[i] = ia_ranges->ia_range[i].sector;
> +				bfqd->nr_sectors[i] =
> +					ia_ranges->ia_range[i].nr_sectors;
> +			}
> +		}
> +	}
> +
> +	/* Otherwise use single-actuator dev info */
> +	if (bfqd->num_actuators == 1) {
> +		bfqd->sector[0] = 0;
> +		bfqd->nr_sectors[0] =
> +			bdev_nr_sectors(dev_to_bdev(disk_to_dev(q->disk)));

get_capacity(q->disk) would be simpler.

> +	}
> +	spin_unlock_irq(&q->queue_lock);
>  
>  	INIT_LIST_HEAD(&bfqd->dispatch);
>  
> diff --git a/block/bfq-iosched.h b/block/bfq-iosched.h
> index 1450990dba32..953980de6b4b 100644
> --- a/block/bfq-iosched.h
> +++ b/block/bfq-iosched.h
> @@ -810,7 +810,13 @@ struct bfq_data {
>  	 * case of single-actuator drives.
>  	 */
>  	unsigned int num_actuators;
> -
> +	/*
> +	 * Disk independent access ranges for each actuator
> +	 * in this device.
> +	 */
> +	sector_t sector[BFQ_MAX_ACTUATORS];
> +	sector_t nr_sectors[BFQ_MAX_ACTUATORS];
> +	struct blk_independent_access_range ia_ranges[BFQ_MAX_ACTUATORS];
>  };
>  
>  enum bfqq_state_flags {

With the nit above fixed,

Reviewed-by: Damien Le Moal <damien.lemoal@xxxxxxxxxxxxxxxxxx>

-- 
Damien Le Moal
Western Digital Research