On 12/6/22 17:41, Paolo Valente wrote:
>
>
>> 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)?
start = 0 and nr_sectors = bdev_nr_sectors(bdev).
No ia_ranges to read.
>
>> 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?
Surely, you can add an "if (bfqd->num_actuators ==1)" optimization in
strategic places to optimize for regular devices with a single actuator,
which bfqd->num_actuators == 1 *exactly* describes. Having
"bfqd->num_actuators = 0" makes no sense to me.
But if you feel strongly about this, feel free to ignore this.
>
> Thanks,
> Paolo
>
>>
>>>
>>> Once again, all other suggestions applied. I'm about to submit a V7.
>>>
>>> Thanks,
>>> Paolo
>>>
>>
>> --
>> Damien Le Moal
>> Western Digital Research
>
--
Damien Le Moal
Western Digital Research
