Re: [PATCH 3/7] blk-mq: add a new queue sysfs attribute async_depth

[Yu Kuai]

Hi,

在 2025/10/2 23:10, Nilay Shroff 写道:
> On 9/30/25 12:41 PM, Yu Kuai wrote:
> > From: Yu Kuai <yukuai3@xxxxxxxxxx>
> >
> > 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 <yukuai3@xxxxxxxxxx>
> > ---
> >   block/blk-core.c       |  1 +
> >   block/blk-mq.c         |  4 ++++
> >   block/blk-sysfs.c      | 47 ++++++++++++++++++++++++++++++++++++++++++
> >   block/elevator.c       |  1 +
> >   include/linux/blkdev.h |  1 +
> >   5 files changed, 54 insertions(+)
> >
> > diff --git a/block/blk-core.c b/block/blk-core.c
> > index dd39ff651095..76df70cfc103 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 09f579414161..260e54fa48f0 100644
> > --- a/block/blk-mq.c
> > +++ b/block/blk-mq.c
> > @@ -529,6 +529,8 @@ static struct request *__blk_mq_alloc_requests(struct blk_mq_alloc_data *data)
> >   			data->rq_flags |= RQF_USE_SCHED;
> >   			if (ops->limit_depth)
> >   				ops->limit_depth(data->cmd_flags, data);
> > +			else if (!blk_mq_sched_sync_request(data->cmd_flags))
> > +				data->shallow_depth = q->async_depth;
> >   		}
> In the subsequent patches, I saw that ->limit_depth is still used for the
> BFQ scheduler. Given that, it seems more consistent to also retain ->limit_depth
> for the mq-deadline and Kyber schedulers, and set data->shallow_depth within their
> respective ->limit_depth methods. If we take this approach, the additional
> blk_mq_sched_sync_request() check above becomes unnecessary.
>
> So IMO:
> - Keep ->limit_depth for all schedulers (bfq, mq-deadline, kyber).
> - Remove the extra blk_mq_sched_sync_request() check from the core code.

I was thinking to save a function call for deadline and kyber, however, I don't
have preference here and I can do this in the next version.

Thanks,
Kuai

> Thanks,
> --Nilay