Re: [PATCH v4 03/29] scsi: core: Make the budget map optional

[Hannes Reinecke <hare@suse.de>]

On 9/12/25 20:21, Bart Van Assche wrote:
> Prepare for not allocating a budget map for pseudo SCSI devices by
> checking whether a budget map has been allocated before using a budget
> map.
> 
> Cc: Hannes Reinecke <hare@suse.de>
> Cc: John Garry <john.g.garry@oracle.com>
> Cc: Ming Lei <ming.lei@redhat.com>
> Signed-off-by: Bart Van Assche <bvanassche@acm.org>
> ---
>   drivers/scsi/scsi.c     |  2 ++
>   drivers/scsi/scsi_lib.c | 14 ++++++++++++--
>   2 files changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
> index 9a0f467264b3..ff6b0973d3b4 100644
> --- a/drivers/scsi/scsi.c
> +++ b/drivers/scsi/scsi.c
> @@ -216,6 +216,8 @@ int scsi_device_max_queue_depth(struct scsi_device *sdev)
>    */
>   int scsi_change_queue_depth(struct scsi_device *sdev, int depth)
>   {
> +	WARN_ON_ONCE(!sdev->budget_map.map);
> +
>   	depth = min_t(int, depth, scsi_device_max_queue_depth(sdev));
>   
>   	if (depth > 0) {
> diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
> index 9c67e04265ce..91a0c7f843c1 100644
> --- a/drivers/scsi/scsi_lib.c
> +++ b/drivers/scsi/scsi_lib.c
> @@ -396,7 +396,8 @@ void scsi_device_unbusy(struct scsi_device *sdev, struct scsi_cmnd *cmd)
>   	if (starget->can_queue > 0)
>   		atomic_dec(&starget->target_busy);
>   
> -	sbitmap_put(&sdev->budget_map, cmd->budget_token);
> +	if (sdev->budget_map.map)
> +		sbitmap_put(&sdev->budget_map, cmd->budget_token);
>   	cmd->budget_token = -1;
>   }
>   
> @@ -1360,6 +1361,14 @@ static inline int scsi_dev_queue_ready(struct request_queue *q,
>   {
>   	int token;
>   
> +	/*
> +	 * Do not allocate a budget token for reserved SCSI commands. Budget
> +	 * tokens are used to enforce the cmd_per_lun limit. That limit does not
> +	 * apply to reserved commands.
> +	 */
> +	if (!sdev->budget_map.map)
> +		return INT_MAX;
> +

Strictly speaking it's not related to reserved commands, but rather to 
cmd_per_lun. Wouldn't it be better to introduce a way to disable 
cmd_per_lun (eg by setting it to INT_MAX or somesuch), and then disable
the budget map when cmd_per_lun is disabled?

Other than that I really like the idea of being able to disable the
budget map. I always wondered if we won't be better off with dropping
the budget map for HBAs with a shared host tagset.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@suse.de                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
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