scsi: scsi_debug: Support hostwide tags

Many SCSI HBAs support a hostwide tagset, whereby each command submitted to
the HW from all submission queues must have a unique tag identifier.

Normally this unique tag will be in the range [0, max queue], where "max
queue" is the depth of each of the submission queues.

Add support for this hostwide tag feature, via module parameter
"host_max_queue". A non-zero value means that the feature is enabled. In
this case, the submission queues are not exposed to upper layer, i.e. from
blk-mq prespective, the device has a single hw queue. There are 2 reasons
for this:

 a. It is assumed that the host can support nr_hw_queues * can_queue
    commands, but this is not true for hostwide tags

 b. For nr_hw_queues != 0, the request tag is not unique over all HW
    queues, and some HBA drivers want to use this tag for the hostwide tag

However, like many SCSI HBA drivers today - megaraid sas being an example -
the full set of HW submission queues are still used in the LLDD driver. So
instead of using a complicated "reply_map" to create a per-CPU submission
queue mapping like megaraid_sas (as it depends on a PCI device + MSIs) -
use a simple algorithm:

    hwq = cpu % queue count

If the host_max_queue param is set non-zero, then the max queue depth is
fixed at this value also.

If and when hostwide shared tags are supported in blk-mq/scsi mid-layer,
then the policy to set nr_hw_queues = 0 for hostwide tags can be revised.

Link: https://lore.kernel.org/r/1594297400-24756-3-git-send-email-john.garry@huawei.com
Acked-by: Douglas Gilbert <dgilbert@interlog.com>
Signed-off-by: John Garry <john.garry@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
index dc8fd6400e4014d07823286b7feac7f1172651bf..802ccd32d010fdc108d34a4bca443a7ac148fa7b 100644 (file)
--- a/drivers/scsi/scsi_debug.c
+++ b/drivers/scsi/scsi_debug.c
@@ -344,6 +344,7 @@ struct sdebug_defer {
        struct execute_work ew;
        int sqa_idx;    /* index of sdebug_queue array */
        int qc_idx;     /* index of sdebug_queued_cmd array within sqa_idx */
+       int hc_idx;     /* hostwide tag index */
        int issuing_cpu;
        bool init_hrt;
        bool init_wq;
@@ -759,6 +760,7 @@ static int sdebug_dsense = DEF_D_SENSE;
 static int sdebug_every_nth = DEF_EVERY_NTH;
 static int sdebug_fake_rw = DEF_FAKE_RW;
 static unsigned int sdebug_guard = DEF_GUARD;
+static int sdebug_host_max_queue;      /* per host */
 static int sdebug_lowest_aligned = DEF_LOWEST_ALIGNED;
 static int sdebug_max_luns = DEF_MAX_LUNS;
 static int sdebug_max_queue = SDEBUG_CANQUEUE; /* per submit queue */
@@ -4707,15 +4709,28 @@ fini:
 
 static struct sdebug_queue *get_queue(struct scsi_cmnd *cmnd)
 {
-       u32 tag = blk_mq_unique_tag(cmnd->request);
-       u16 hwq = blk_mq_unique_tag_to_hwq(tag);
+       u16 hwq;
 
-       pr_debug("tag=%#x, hwq=%d\n", tag, hwq);
-       if (WARN_ON_ONCE(hwq >= submit_queues))
-               hwq = 0;
+       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);
+
+               pr_debug("tag=%#x, hwq=%d\n", tag, hwq);
+               if (WARN_ON_ONCE(hwq >= submit_queues))
+                       hwq = 0;
+       }
        return sdebug_q_arr + hwq;
 }
 
+static u32 get_tag(struct scsi_cmnd *cmnd)
+{
+       return blk_mq_unique_tag(cmnd->request);
+}
+
 /* Queued (deferred) command completions converge here. */
 static void sdebug_q_cmd_complete(struct sdebug_defer *sd_dp)
 {
@@ -4747,8 +4762,8 @@ static void sdebug_q_cmd_complete(struct sdebug_defer *sd_dp)
        scp = sqcp->a_cmnd;
        if (unlikely(scp == NULL)) {
                spin_unlock_irqrestore(&sqp->qc_lock, iflags);
-               pr_err("scp is NULL, sqa_idx=%d, qc_idx=%d\n",
-                      sd_dp->sqa_idx, qc_idx);
+               pr_err("scp is NULL, sqa_idx=%d, qc_idx=%d, hc_idx=%d\n",
+                      sd_dp->sqa_idx, qc_idx, sd_dp->hc_idx);
                return;
        }
        devip = (struct sdebug_dev_info *)scp->device->hostdata;
@@ -5451,6 +5466,10 @@ static int schedule_resp(struct scsi_cmnd *cmnd, struct sdebug_dev_info *devip,
                new_sd_dp = false;
        }
 
+       /* Set the hostwide tag */
+       if (sdebug_host_max_queue)
+               sd_dp->hc_idx = get_tag(cmnd);
+
        if (ndelay > 0 && ndelay < INCLUSIVE_TIMING_MAX_NS)
                ns_from_boot = ktime_get_boottime_ns();
 
@@ -5572,6 +5591,7 @@ module_param_named(every_nth, sdebug_every_nth, int, S_IRUGO | S_IWUSR);
 module_param_named(fake_rw, sdebug_fake_rw, int, S_IRUGO | S_IWUSR);
 module_param_named(guard, sdebug_guard, uint, S_IRUGO);
 module_param_named(host_lock, sdebug_host_lock, bool, S_IRUGO | S_IWUSR);
+module_param_named(host_max_queue, sdebug_host_max_queue, int, S_IRUGO);
 module_param_string(inq_product, sdebug_inq_product_id,
                    sizeof(sdebug_inq_product_id), S_IRUGO | S_IWUSR);
 module_param_string(inq_rev, sdebug_inq_product_rev,
@@ -5642,6 +5662,8 @@ MODULE_PARM_DESC(every_nth, "timeout every nth command(def=0)");
 MODULE_PARM_DESC(fake_rw, "fake reads/writes instead of copying (def=0)");
 MODULE_PARM_DESC(guard, "protection checksum: 0=crc, 1=ip (def=0)");
 MODULE_PARM_DESC(host_lock, "host_lock is ignored (def=0)");
+MODULE_PARM_DESC(host_max_queue,
+                "host max # of queued cmds (0 to max(def) [max_queue fixed equal for !0])");
 MODULE_PARM_DESC(inq_product, "SCSI INQUIRY product string (def=\"scsi_debug\")");
 MODULE_PARM_DESC(inq_rev, "SCSI INQUIRY revision string (def=\""
                 SDEBUG_VERSION "\")");
@@ -6141,7 +6163,8 @@ static ssize_t max_queue_store(struct device_driver *ddp, const char *buf,
        struct sdebug_queue *sqp;
 
        if ((count > 0) && (1 == sscanf(buf, "%d", &n)) && (n > 0) &&
-           (n <= SDEBUG_CANQUEUE)) {
+           (n <= SDEBUG_CANQUEUE) &&
+           (sdebug_host_max_queue == 0)) {
                block_unblock_all_queues(true);
                k = 0;
                for (j = 0, sqp = sdebug_q_arr; j < submit_queues;
@@ -6164,6 +6187,17 @@ static ssize_t max_queue_store(struct device_driver *ddp, const char *buf,
 }
 static DRIVER_ATTR_RW(max_queue);
 
+static ssize_t host_max_queue_show(struct device_driver *ddp, char *buf)
+{
+       return scnprintf(buf, PAGE_SIZE, "%d\n", sdebug_host_max_queue);
+}
+
+/*
+ * Since this is used for .can_queue, and we get the hc_idx tag from the bitmap
+ * in range [0, sdebug_host_max_queue), we can't change it.
+ */
+static DRIVER_ATTR_RO(host_max_queue);
+
 static ssize_t no_uld_show(struct device_driver *ddp, char *buf)
 {
        return scnprintf(buf, PAGE_SIZE, "%d\n", sdebug_no_uld);
@@ -6503,6 +6537,7 @@ static struct attribute *sdebug_drv_attrs[] = {
        &driver_attr_ptype.attr,
        &driver_attr_dsense.attr,
        &driver_attr_fake_rw.attr,
+       &driver_attr_host_max_queue.attr,
        &driver_attr_no_lun_0.attr,
        &driver_attr_num_tgts.attr,
        &driver_attr_dev_size_mb.attr,
@@ -6619,6 +6654,20 @@ static int __init scsi_debug_init(void)
                return -EINVAL;
        }
 
+       if ((sdebug_host_max_queue > SDEBUG_CANQUEUE) ||
+           (sdebug_host_max_queue < 0)) {
+               pr_err("host_max_queue must be in range [0 %d]\n",
+                      SDEBUG_CANQUEUE);
+               return -EINVAL;
+       }
+
+       if (sdebug_host_max_queue &&
+           (sdebug_max_queue != sdebug_host_max_queue)) {
+               sdebug_max_queue = sdebug_host_max_queue;
+               pr_warn("fixing max submit queue depth to host max queue depth, %d\n",
+                       sdebug_max_queue);
+       }
+
        sdebug_q_arr = kcalloc(submit_queues, sizeof(struct sdebug_queue),
                               GFP_KERNEL);
        if (sdebug_q_arr == NULL)
@@ -7257,7 +7306,10 @@ static int sdebug_driver_probe(struct device *dev)
 
        sdbg_host = to_sdebug_host(dev);
 
-       sdebug_driver_template.can_queue = sdebug_max_queue;
+       if (sdebug_host_max_queue)
+               sdebug_driver_template.can_queue = sdebug_host_max_queue;
+       else
+               sdebug_driver_template.can_queue = sdebug_max_queue;
        if (!sdebug_clustering)
                sdebug_driver_template.dma_boundary = PAGE_SIZE - 1;
 
@@ -7272,9 +7324,13 @@ static int sdebug_driver_probe(struct device *dev)
                        my_name, submit_queues, nr_cpu_ids);
                submit_queues = nr_cpu_ids;
        }
-       /* Decide whether to tell scsi subsystem that we want mq */
-       /* Following should give the same answer for each host */
-       hpnt->nr_hw_queues = submit_queues;
+       /*
+        * 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.
+        */
+       if (!sdebug_host_max_queue)
+               hpnt->nr_hw_queues = submit_queues;
 
        sdbg_host->shost = hpnt;
        *((struct sdebug_host_info **)hpnt->hostdata) = sdbg_host;