[v5,4/8] blk-mq: introduce blk_mq_map_hw_queues

blk_mq_pci_map_queues and blk_mq_virtio_map_queues will create a CPU to
hardware queue mapping based on affinity information. These two function
share common code and only differ on how the affinity information is
retrieved. Also, those functions are located in the block subsystem
where it doesn't really fit in. They are virtio and pci subsystem
specific.

Thus introduce provide a generic mapping function which uses the
irq_get_affinity callback from bus_type.

Originally idea from Ming Lei <ming.lei@redhat.com>

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Daniel Wagner <wagi@kernel.org>
---
 block/blk-mq-cpumap.c  | 37 +++++++++++++++++++++++++++++++++++++
 include/linux/blk-mq.h |  2 ++
 2 files changed, 39 insertions(+)

On Fri, Nov 15, 2024 at 05:37:48PM +0100, Daniel Wagner wrote:
> blk_mq_pci_map_queues and blk_mq_virtio_map_queues will create a CPU to
> hardware queue mapping based on affinity information. These two function
> share common code and only differ on how the affinity information is
> retrieved. Also, those functions are located in the block subsystem
> where it doesn't really fit in. They are virtio and pci subsystem
> specific.
> 
> Thus introduce provide a generic mapping function which uses the
> irq_get_affinity callback from bus_type.
> 
> Originally idea from Ming Lei <ming.lei@redhat.com>
> 
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Hannes Reinecke <hare@suse.de>
> Signed-off-by: Daniel Wagner <wagi@kernel.org>

Reviewed-by: Ming Lei <ming.lei@redhat.com>

On 15/11/2024 16:37, Daniel Wagner wrote:
> blk_mq_pci_map_queues and blk_mq_virtio_map_queues will create a CPU to
> hardware queue mapping based on affinity information. These two function
> share common code and only differ on how the affinity information is
> retrieved. Also, those functions are located in the block subsystem
> where it doesn't really fit in. They are virtio and pci subsystem
> specific.
> 
> Thus introduce provide a generic mapping function which uses the
> irq_get_affinity callback from bus_type.
> 
> Originally idea from Ming Lei <ming.lei@redhat.com>
> 
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Hannes Reinecke <hare@suse.de>
> Signed-off-by: Daniel Wagner <wagi@kernel.org>

Just a couple of styling queries/comments, below:
Reviewed-by: John Garry <john.g.garry@oracle.com>

> ---
>   block/blk-mq-cpumap.c  | 37 +++++++++++++++++++++++++++++++++++++
>   include/linux/blk-mq.h |  2 ++
>   2 files changed, 39 insertions(+)
> 
> diff --git a/block/blk-mq-cpumap.c b/block/blk-mq-cpumap.c
> index 9638b25fd52124f0173e968ebdca5f1fe0b42ad9..0b65ffa5a183cc8e6697df4a16748eff15bfa8b3 100644
> --- a/block/blk-mq-cpumap.c
> +++ b/block/blk-mq-cpumap.c
> @@ -11,6 +11,7 @@
>   #include <linux/smp.h>
>   #include <linux/cpu.h>
>   #include <linux/group_cpus.h>
> +#include <linux/device/bus.h>
>   
>   #include "blk.h"
>   #include "blk-mq.h"
> @@ -54,3 +55,39 @@ int blk_mq_hw_queue_to_node(struct blk_mq_queue_map *qmap, unsigned int index)
>   
>   	return NUMA_NO_NODE;
>   }
> +
> +/**
> + * blk_mq_map_hw_queues - Create CPU to hardware queue mapping
> + * @qmap:	CPU to hardware queue map.
> + * @dev:	The device to map queues.
> + * @offset:	Queue offset to use for the device.

supernit: maybe no '.'

> + *
> + * Create a CPU to hardware queue mapping in @qmap. The struct bus_type
> + * irq_get_affinity callback will be used to retrieve the affinity.
> + */
> +void blk_mq_map_hw_queues(struct blk_mq_queue_map *qmap,
> +			  struct device *dev, unsigned int offset)
> +
> +{
> +	const struct cpumask *mask;
> +	unsigned int queue, cpu;
> +
> +	if (!dev->bus->irq_get_affinity)
> +		goto fallback;
> +
> +	for (queue = 0; queue < qmap->nr_queues; queue++) {
> +		mask = dev->bus->irq_get_affinity(dev, queue + offset);
> +		if (!mask)
> +			goto fallback;
> +
> +		for_each_cpu(cpu, mask)
> +			qmap->mq_map[cpu] = qmap->queue_offset + queue;
> +	}
> +
> +	return;
> +
> +fallback:
> +	WARN_ON_ONCE(qmap->nr_queues > 1);
> +	blk_mq_clear_mq_map(qmap);
> +}
> +EXPORT_SYMBOL_GPL(blk_mq_map_hw_queues);

is there still a blank line at the bottom of the file?

> diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
> index 2035fad3131fb60781957095ce8a3a941dd104be..05f544a9ed873d2f96d72c18e124c94146f6943f 100644
> --- a/include/linux/blk-mq.h
> +++ b/include/linux/blk-mq.h
> @@ -923,6 +923,8 @@ void blk_mq_unfreeze_queue_non_owner(struct request_queue *q);
>   void blk_freeze_queue_start_non_owner(struct request_queue *q);
>   
>   void blk_mq_map_queues(struct blk_mq_queue_map *qmap);
> +void blk_mq_map_hw_queues(struct blk_mq_queue_map *qmap,
> +			  struct device *dev, unsigned int offset);
>   void blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, int nr_hw_queues);
>   
>   void blk_mq_quiesce_queue_nowait(struct request_queue *q);
>