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

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Date:   Tue, 6 Dec 2022 09:06:17 +0100
From:   Paolo Valente <paolo.valente@...aro.org>
To:     Damien Le Moal <damien.lemoal@...nsource.wdc.com>
Cc:     Jens Axboe <axboe@...nel.dk>,
        linux-block <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



> Il giorno 21 nov 2022, alle ore 02:01, Damien Le Moal <damien.lemoal@...nsource.wdc.com> ha scritto:
> 

...

> 
>> }
>> 
>> 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.

Actually, IIUC this assignment to 0 seems to be done exactly when you
say that it should be done, i.e., when the disk does not provide any
range information (ia_ranges is NULL). Am I missing something else?

Once again, all other suggestions applied. I'm about to submit a V7.

Thanks,
Paolo