> Il giorno 6 dic 2022, alle ore 09:29, Damien Le Moal <damien.lemoal@xxxxxxxxxxxxxxxxxx> ha scritto:
>
> On 12/6/22 17:06, Paolo Valente wrote:
>>
>>
>>> Il giorno 21 nov 2022, alle ore 02:01, Damien Le Moal <damien.lemoal@xxxxxxxxxxxxxxxxxx> 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?
>
> No ranges reported means no extra actuators, so a single actuator an
> single LBA range for the entire device.
I'm still confused, sorry. Where will I read sector ranges from, if
no sector range information is available (ia_ranges is NULL)?
> In that case, bfq should process
> all IOs using bfqd->ia_ranges[0]. The get range function will always
> return that range. That makes the code clean and avoids different path for
> nr_ranges == 1 and nr_ranges > 1. No ?
Apart from the above point, for which maybe there is some other
source of information for getting ranges, I see the following issue.
What you propose is to save sector information and trigger the
range-checking for loop also for the above single-actuator case. Yet
txecuting (one iteration of) that loop will will always result in
getting a 0 as index. So, what's the point is saving data and
executing code on each IO, for getting a static result that we already
know we will get?
Thanks,
Paolo
>
>>
>> Once again, all other suggestions applied. I'm about to submit a V7.
>>
>> Thanks,
>> Paolo
>>
>
> --
> Damien Le Moal
> Western Digital Research
