[PATCH v8 15/18] scsi: scsi_debug: Support host tagset

[John Garry]

When host_max_queue is set (> 0), set the Scsi_Host.host_tagset such that
blk-mq will use a hostwide tagset over all SCSI host submission queues.

This means that we may expose all submission queues and always use the hwq
chosen by blk-mq.

And since if sdebug_host_max_queue is set, sdebug_max_queue is fixed to the
same value, we can simplify how sdebug_driver_template.can_queue is set.

Signed-off-by: John Garry <john.ga...@huawei.com>
---
 drivers/scsi/scsi_debug.c | 28 ++++++++++------------------
 1 file changed, 10 insertions(+), 18 deletions(-)

diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
index 064ed680c053..4238baa2b34b 100644
--- a/drivers/scsi/scsi_debug.c
+++ b/drivers/scsi/scsi_debug.c
@@ -4698,19 +4698,14 @@ static int resp_rwp_zone(struct scsi_cmnd *scp, struct 
sdebug_dev_info *devip)
 static struct sdebug_queue *get_queue(struct scsi_cmnd *cmnd)
 {
        u16 hwq;
+       u32 tag = blk_mq_unique_tag(cmnd->request);
 
-       if (sdebug_host_max_queue) {
-               /* Provide a simple method to choose the hwq */
-               hwq = smp_processor_id() % submit_queues;
-       } else {
-               u32 tag = blk_mq_unique_tag(cmnd->request);
+       hwq = blk_mq_unique_tag_to_hwq(tag);
 
-               hwq = blk_mq_unique_tag_to_hwq(tag);
+       pr_debug("tag=%#x, hwq=%d\n", tag, hwq);
+       if (WARN_ON_ONCE(hwq >= submit_queues))
+               hwq = 0;
 
-               pr_debug("tag=%#x, hwq=%d\n", tag, hwq);
-               if (WARN_ON_ONCE(hwq >= submit_queues))
-                       hwq = 0;
-       }
        return sdebug_q_arr + hwq;
 }
 
@@ -7347,10 +7342,7 @@ static int sdebug_driver_probe(struct device *dev)
 
        sdbg_host = to_sdebug_host(dev);
 
-       if (sdebug_host_max_queue)
-               sdebug_driver_template.can_queue = sdebug_host_max_queue;
-       else
-               sdebug_driver_template.can_queue = sdebug_max_queue;
+       sdebug_driver_template.can_queue = sdebug_max_queue;
        if (!sdebug_clustering)
                sdebug_driver_template.dma_boundary = PAGE_SIZE - 1;
 
@@ -7367,11 +7359,11 @@ static int sdebug_driver_probe(struct device *dev)
        }
        /*
         * Decide whether to tell scsi subsystem that we want mq. The
-        * following should give the same answer for each host. If the host
-        * has a limit of hostwide max commands, then do not set.
+        * following should give the same answer for each host.
         */
-       if (!sdebug_host_max_queue)
-               hpnt->nr_hw_queues = submit_queues;
+       hpnt->nr_hw_queues = submit_queues;
+       if (sdebug_host_max_queue)
+               hpnt->host_tagset = 1;
 
        sdbg_host->shost = hpnt;
        *((struct sdebug_host_info **)hpnt->hostdata) = sdbg_host;
-- 
2.26.2