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Message-Id: <ca0d1a5f-3427-4833-aa50-f74c0bde52e1@fnnas.com>
Date: Fri, 21 Nov 2025 20:17:42 +0800
From: "Yu Kuai" <yukuai@...as.com>
To: "Hannes Reinecke" <hare@...e.de>, <axboe@...nel.dk>,
<nilay@...ux.ibm.com>, <bvanassche@....org>,
<linux-block@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
"Yu Kuai" <yukuai@...as.com>
Subject: Re: [PATCH v6 4/8] blk-mq: add a new queue sysfs attribute async_depth
Hi,
在 2025/11/21 15:14, Hannes Reinecke 写道:
> On 11/21/25 06:28, Yu Kuai wrote:
>> Add a new field async_depth to request_queue and related APIs, this is
>> currently not used, following patches will convert elevators to use
>> this instead of internal async_depth.
>>
>> Signed-off-by: Yu Kuai <yukuai@...as.com>
>> Reviewed-by: Nilay Shroff <nilay@...ux.ibm.com>
>> ---
>> block/blk-core.c | 1 +
>> block/blk-mq.c | 6 ++++++
>> block/blk-sysfs.c | 42 ++++++++++++++++++++++++++++++++++++++++++
>> block/elevator.c | 1 +
>> include/linux/blkdev.h | 1 +
>> 5 files changed, 51 insertions(+)
>>
>> diff --git a/block/blk-core.c b/block/blk-core.c
>> index 14ae73eebe0d..cc5c9ced8e6f 100644
>> --- a/block/blk-core.c
>> +++ b/block/blk-core.c
>> @@ -463,6 +463,7 @@ struct request_queue *blk_alloc_queue(struct
>> queue_limits *lim, int node_id)
>> fs_reclaim_release(GFP_KERNEL);
>> q->nr_requests = BLKDEV_DEFAULT_RQ;
>> + q->async_depth = BLKDEV_DEFAULT_RQ;
>> return q;
>> diff --git a/block/blk-mq.c b/block/blk-mq.c
>> index 6c505ebfab65..ae6ce68f4786 100644
>> --- a/block/blk-mq.c
>> +++ b/block/blk-mq.c
>> @@ -4628,6 +4628,7 @@ int blk_mq_init_allocated_queue(struct
>> blk_mq_tag_set *set,
>> spin_lock_init(&q->requeue_lock);
>> q->nr_requests = set->queue_depth;
>> + q->async_depth = set->queue_depth;
>> blk_mq_init_cpu_queues(q, set->nr_hw_queues);
>> blk_mq_map_swqueue(q);
>> @@ -4994,6 +4995,11 @@ struct elevator_tags
>> *blk_mq_update_nr_requests(struct request_queue *q,
>> q->elevator->et = et;
>> }
>> + /*
>> + * Preserve relative value, both nr and async_depth are at most
>> 16 bit
>> + * value, no need to worry about overflow.
>> + */
>> + q->async_depth = max(q->async_depth * nr / q->nr_requests, 1);
>> q->nr_requests = nr;
>> if (q->elevator && q->elevator->type->ops.depth_updated)
>> q->elevator->type->ops.depth_updated(q);
>> diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
>> index 8684c57498cc..5c2d29ac6570 100644
>> --- a/block/blk-sysfs.c
>> +++ b/block/blk-sysfs.c
>> @@ -127,6 +127,46 @@ queue_requests_store(struct gendisk *disk, const
>> char *page, size_t count)
>> return ret;
>> }
>> +static ssize_t queue_async_depth_show(struct gendisk *disk, char
>> *page)
>> +{
>> + guard(mutex)(&disk->queue->elevator_lock);
>> +
>> + return queue_var_show(disk->queue->async_depth, page);
>> +}
>> +
>> +static ssize_t
>> +queue_async_depth_store(struct gendisk *disk, const char *page,
>> size_t count)
>> +{
>> + struct request_queue *q = disk->queue;
>> + unsigned int memflags;
>> + unsigned long nr;
>> + int ret;
>> +
>> + if (!queue_is_mq(q))
>> + return -EINVAL;
>> +
>> + ret = queue_var_store(&nr, page, count);
>> + if (ret < 0)
>> + return ret;
>> +
>> + if (nr == 0)
>> + return -EINVAL;
>> +
>> + memflags = blk_mq_freeze_queue(q);
>> + scoped_guard(mutex, &q->elevator_lock) {
>> + if (q->elevator) {
>> + q->async_depth = min(q->nr_requests, nr);
>> + if (q->elevator->type->ops.depth_updated)
>> + q->elevator->type->ops.depth_updated(q);
>> + } else {
>> + ret = -EINVAL;
>> + }
>> + }
>> + blk_mq_unfreeze_queue(q, memflags);
>> +
>> + return ret;
>> +}
>> +
>> static ssize_t queue_ra_show(struct gendisk *disk, char *page)
>> {
>> ssize_t ret;
>> @@ -532,6 +572,7 @@ static struct queue_sysfs_entry _prefix##_entry =
>> { \
>> }
>> QUEUE_RW_ENTRY(queue_requests, "nr_requests");
>> +QUEUE_RW_ENTRY(queue_async_depth, "async_depth");
>> QUEUE_RW_ENTRY(queue_ra, "read_ahead_kb");
>> QUEUE_LIM_RW_ENTRY(queue_max_sectors, "max_sectors_kb");
>> QUEUE_LIM_RO_ENTRY(queue_max_hw_sectors, "max_hw_sectors_kb");
>> @@ -754,6 +795,7 @@ static struct attribute *blk_mq_queue_attrs[] = {
>> */
>> &elv_iosched_entry.attr,
>> &queue_requests_entry.attr,
>> + &queue_async_depth_entry.attr,
>> #ifdef CONFIG_BLK_WBT
>> &queue_wb_lat_entry.attr,
>> #endif
>> diff --git a/block/elevator.c b/block/elevator.c
>> index 5b37ef44f52d..5ff21075a84a 100644
>> --- a/block/elevator.c
>> +++ b/block/elevator.c
>> @@ -589,6 +589,7 @@ static int elevator_switch(struct request_queue
>> *q, struct elv_change_ctx *ctx)
>> blk_queue_flag_clear(QUEUE_FLAG_SQ_SCHED, q);
>> q->elevator = NULL;
>> q->nr_requests = q->tag_set->queue_depth;
>> + q->async_depth = q->tag_set->queue_depth;
>> }
>> blk_add_trace_msg(q, "elv switch: %s", ctx->name);
>> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
>> index cdc68c41fa96..edddf17f8304 100644
>> --- a/include/linux/blkdev.h
>> +++ b/include/linux/blkdev.h
>> @@ -552,6 +552,7 @@ struct request_queue {
>> * queue settings
>> */
>> unsigned int nr_requests; /* Max # of requests */
>> + unsigned int async_depth; /* Max # of async requests */
>> #ifdef CONFIG_BLK_INLINE_ENCRYPTION
>> struct blk_crypto_profile *crypto_profile;
>
> Hmm. Makes me wonder: async_depth is only used within the elevators, so
> maybe we should restrict visibility of that attribute when an elevator
> is selected?
> It feels kinda awkward having an attribute which does nothing if no
> elevator is loaded ...
To be honest, I can't think of how to implement this suitably, we'll have
to remove/create this entry while switching elevator, this doesn't seem
worth it to invent a new wheel.
>
> Cheers,
>
> Hannes
--
Thanks,
Kuai
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