Re: [PATCH v2 2/2] block/mq-deadline: Fix the tag reservation code

[Bart Van Assche <bvanassche@acm.org>]

On 5/16/24 02:14, YangYang wrote:
>> @@ -513,9 +527,9 @@ static void dd_depth_updated(struct blk_mq_hw_ctx 
>> *hctx)
>>       struct deadline_data *dd = q->elevator->elevator_data;
>>       struct blk_mq_tags *tags = hctx->sched_tags;
>> -    dd->async_depth = max(1UL, 3 * q->nr_requests / 4);
>> +    dd->async_depth = q->nr_requests;
>> -    sbitmap_queue_min_shallow_depth(&tags->bitmap_tags, 
>> dd->async_depth);
>> +    sbitmap_queue_min_shallow_depth(&tags->bitmap_tags, 1);
> 
> If sbq->min_shallow_depth is set to 1, sbq->wake_batch will also be set
> to 1. I guess this may result in batch wakeup not working as expected.

The value of the sbq->min_shallow_depth parameter may affect performance
but does not affect correctness. See also the comment above the
sbitmap_queue_min_shallow_depth() declaration. Is this sufficient to
address your concern?

Thanks,

Bart.