Re: [PATCH 10/24] scsi: allocate separate queue for reserved commands

[John Garry]

On 29/05/2019 14:28, Hannes Reinecke wrote:
From: Hannes Reinecke <h...@suse.com>
Allocate a separate 'reserved_cmd_q' for sending reserved commands.

Signed-off-by: Hannes Reinecke <h...@suse.com>
---
 drivers/scsi/scsi_lib.c  | 15 ++++++++++++++-
 include/scsi/scsi_host.h |  4 ++++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index e17153a9ce7c..076459853622 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1831,6 +1831,7 @@ struct request_queue *scsi_mq_alloc_queue(struct 
scsi_device *sdev)
 int scsi_mq_setup_tags(struct Scsi_Host *shost)
 {
        unsigned int cmd_size, sgl_size;
+       int ret;

        sgl_size = scsi_mq_inline_sgl_size(shost);
        cmd_size = sizeof(struct scsi_cmnd) + shost->hostt->cmd_size + sgl_size;
@@ -1850,11 +1851,23 @@ int scsi_mq_setup_tags(struct Scsi_Host *shost)
                BLK_ALLOC_POLICY_TO_MQ_FLAG(shost->hostt->tag_alloc_policy);
        shost->tag_set.driver_data = shost;

-       return blk_mq_alloc_tag_set(&shost->tag_set);
+       ret = blk_mq_alloc_tag_set(&shost->tag_set);
+       if (ret)
+               return ret;
+
+       if (shost->nr_reserved_cmds && shost->use_reserved_cmd_q) {
+               shost->reserved_cmd_q = blk_mq_init_queue(&shost->tag_set);
+               if (IS_ERR(shost->reserved_cmd_q)) {
+                       blk_mq_free_tag_set(&shost->tag_set);
+                       ret = PTR_ERR(shost->reserved_cmd_q);
+               }
+       }
+       return ret;
 }

 void scsi_mq_destroy_tags(struct Scsi_Host *shost)
 {
+       blk_cleanup_queue(shost->reserved_cmd_q);
        blk_mq_free_tag_set(&shost->tag_set);
 }

diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index 89998b6bee04..a2bab5f07eff 100644
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -600,6 +600,7 @@ struct Scsi_Host {
         * Number of reserved commands, if any.
         */
        unsigned nr_reserved_cmds;
+       struct request_queue *reserved_cmd_q;

        unsigned active_mode:2;
        unsigned unchecked_isa_dma:1;
@@ -637,6 +638,9 @@ struct Scsi_Host {
        /* The transport requires the LUN bits NOT to be stored in CDB[1] */
        unsigned no_scsi2_lun_in_cdb:1;

+       /* Host requires a separate reserved_cmd_q */
+       unsigned use_reserved_cmd_q:1;

Is this really required? I would think that a non-zero value for 
shost->nr_reserved_cmds means the same thing in practice.

Thanks,
John

+
        /*
         * Optional work queue to be utilized by the transport
         */