Re: [PATCH v2 06/20] scsi: core: Add support for reserved tags

John Garry
2021-11-22T08:15:42Z

On 19/11/2021 19:57, Bart Van Assche wrote:
> Allow SCSI LLDs to allocate reserved tags by passing the BLK_MQ_REQ_RESERVED
> flag to blk_mq_alloc_request().
>
> Cc: Hannes Reinecke <hare@suse.de>
> Cc: John Garry <john.garry@huawei.com>
> Signed-off-by: Bart Van Assche <bvanassche@acm.org > ---
> drivers/scsi/scsi_lib.c | 4 +++-
> include/scsi/scsi_host.h | 9 ++++++++-
> 2 files changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 59c3c4fbcfc0..44489ddc646c 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -1925,6 +1925,7 @@ int scsi_mq_setup_tags(struct Scsi_Host *shost)
> {
> unsigned int cmd_size, sgl_size;
> struct blk_mq_tag_set *tag_set = &shost->tag_set;
> + unsigned int reserved_tags = shost->hostt->reserved_tags;
>
> sgl_size = max_t(unsigned int, sizeof(struct scatterlist),
> scsi_mq_inline_sgl_size(shost));
> @@ -1940,7 +1941,8 @@ int scsi_mq_setup_tags(struct Scsi_Host *shost)
> tag_set->ops = &scsi_mq_ops_no_commit;
> tag_set->nr_hw_queues = shost->nr_hw_queues ? : 1;
> tag_set->nr_maps = shost->nr_maps ? : 1;
> - tag_set->queue_depth = shost->can_queue;
> + tag_set->queue_depth = shost->can_queue + reserved_tags;
> + tag_set->reserved_tags = reserved_tags;
> tag_set->cmd_size = cmd_size;
> tag_set->numa_node = NUMA_NO_NODE;
> tag_set->flags = BLK_MQ_F_SHOULD_MERGE;
> diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
> index 72e1a347baa6..ec0f7705e06a 100644
> --- a/include/scsi/scsi_host.h
> +++ b/include/scsi/scsi_host.h
> @@ -367,10 +367,17 @@ struct scsi_host_template {

why no field in struct Scsi_Host?

> /*
> * This determines if we will use a non-interrupt driven
> * or an interrupt driven scheme. It is set to the maximum number
> - * of simultaneous commands a single hw queue in HBA will accept.
> + * of simultaneous commands a single hw queue in HBA will accept. Does
> + * not include @reserved_tags.
> */
> int can_queue;
>
> + /*
> + * Number of tags to reserve.

> A reserved tag can be allocated by passing
> + * the BLK_MQ_REQ_RESERVED flag to blk_get_request().

I don't see why we need this comment.

> + */
> + unsigned reserved_tags;

I thought that unsigned int was preferred

> +
> /*
> * In many instances, especially where disconnect / reconnect are
> * supported, our host also has an ID on the SCSI bus. If this is
> .
>