scsi: cxlflash: Introduce hardware queue steering

As an enhancement to distribute requests to multiple hardware queues, add the
infrastructure to hash a SCSI command into a particular hardware queue.
Support the following scenarios when deriving which queue to use: single
queue, tagging when SCSI-MQ enabled, and simple hash via CPU ID when SCSI-MQ
is disabled. Rather than altering the existing send API, the derived hardware
queue is stored in the AFU command where it can be used for sending a command
to the chosen hardware queue.

Signed-off-by: Matthew R. Ochs <mrochs@linux.vnet.ibm.com>
Signed-off-by: Uma Krishnan <ukrishn@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/cxlflash/common.h

@@ -96,6 +96,13 @@ enum cxlflash_state {
 	STATE_FAILTERM	/* Failed/terminating state, error out users/threads */
 };
 
+enum cxlflash_hwq_mode {
+	HWQ_MODE_RR,	/* Roundrobin (default) */
+	HWQ_MODE_TAG,	/* Distribute based on block MQ tag */
+	HWQ_MODE_CPU,	/* CPU affinity */
+	MAX_HWQ_MODE
+};
+
 /*
  * Each context has its own set of resource handles that is visible
  * only from that context.
@@ -146,9 +153,9 @@ struct afu_cmd {
 	struct scsi_cmnd *scp;
 	struct completion cevent;
 	struct list_head queue;
+	u32 hwq_index;
 
 	u8 cmd_tmf:1;
-	u32 hwq_index;
 
 	/* As per the SISLITE spec the IOARCB EA has to be 16-byte aligned.
 	 * However for performance reasons the IOARCB/IOASA should be
@@ -213,8 +220,11 @@ struct afu {
 	atomic_t cmds_active;	/* Number of currently active AFU commands */
 	u64 hb;
 	u32 internal_lun;	/* User-desired LUN mode for this AFU */
+
 	u32 num_hwqs;		/* Number of hardware queues */
 	u32 desired_hwqs;	/* Desired h/w queues, effective on AFU reset */
+	enum cxlflash_hwq_mode hwq_mode; /* Steering mode for h/w queues */
+	u32 hwq_rr_count;	/* Count to distribute traffic for roundrobin */
 
 	char version[16];
 	u64 interface_version;

drivers/scsi/cxlflash/main.c

@@ -357,6 +357,43 @@ static int wait_resp(struct afu *afu, struct afu_cmd *cmd)
 	return rc;
 }
 
+/**
+ * cmd_to_target_hwq() - selects a target hardware queue for a SCSI command
+ * @host:	SCSI host associated with device.
+ * @scp:	SCSI command to send.
+ * @afu:	SCSI command to send.
+ *
+ * Hashes a command based upon the hardware queue mode.
+ *
+ * Return: Trusted index of target hardware queue
+ */
+static u32 cmd_to_target_hwq(struct Scsi_Host *host, struct scsi_cmnd *scp,
+			     struct afu *afu)
+{
+	u32 tag;
+	u32 hwq = 0;
+
+	if (afu->num_hwqs == 1)
+		return 0;
+
+	switch (afu->hwq_mode) {
+	case HWQ_MODE_RR:
+		hwq = afu->hwq_rr_count++ % afu->num_hwqs;
+		break;
+	case HWQ_MODE_TAG:
+		tag = blk_mq_unique_tag(scp->request);
+		hwq = blk_mq_unique_tag_to_hwq(tag);
+		break;
+	case HWQ_MODE_CPU:
+		hwq = smp_processor_id() % afu->num_hwqs;
+		break;
+	default:
+		WARN_ON_ONCE(1);
+	}
+
+	return hwq;
+}
+
 /**
  * send_tmf() - sends a Task Management Function (TMF)
  * @afu:	AFU to checkout from.
@@ -368,10 +405,12 @@ static int wait_resp(struct afu *afu, struct afu_cmd *cmd)
  */
 static int send_tmf(struct afu *afu, struct scsi_cmnd *scp, u64 tmfcmd)
 {
-	struct cxlflash_cfg *cfg = shost_priv(scp->device->host);
+	struct Scsi_Host *host = scp->device->host;
+	struct cxlflash_cfg *cfg = shost_priv(host);
 	struct afu_cmd *cmd = sc_to_afucz(scp);
 	struct device *dev = &cfg->dev->dev;
-	struct hwq *hwq = get_hwq(afu, PRIMARY_HWQ);
+	int hwq_index = cmd_to_target_hwq(host, scp, afu);
+	struct hwq *hwq = get_hwq(afu, hwq_index);
 	ulong lock_flags;
 	int rc = 0;
 	ulong to;
@@ -388,7 +427,7 @@ static int send_tmf(struct afu *afu, struct scsi_cmnd *scp, u64 tmfcmd)
 	cmd->scp = scp;
 	cmd->parent = afu;
 	cmd->cmd_tmf = true;
-	cmd->hwq_index = hwq->index;
+	cmd->hwq_index = hwq_index;
 
 	cmd->rcb.ctx_id = hwq->ctx_hndl;
 	cmd->rcb.msi = SISL_MSI_RRQ_UPDATED;
@@ -448,7 +487,8 @@ static int cxlflash_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *scp)
 	struct device *dev = &cfg->dev->dev;
 	struct afu_cmd *cmd = sc_to_afucz(scp);
 	struct scatterlist *sg = scsi_sglist(scp);
-	struct hwq *hwq = get_hwq(afu, PRIMARY_HWQ);
+	int hwq_index = cmd_to_target_hwq(host, scp, afu);
+	struct hwq *hwq = get_hwq(afu, hwq_index);
 	u16 req_flags = SISL_REQ_FLAGS_SUP_UNDERRUN;
 	ulong lock_flags;
 	int rc = 0;
@@ -498,7 +538,7 @@ static int cxlflash_queuecommand(struct Scsi_Host *host, struct scsi_cmnd *scp)
 
 	cmd->scp = scp;
 	cmd->parent = afu;
-	cmd->hwq_index = hwq->index;
+	cmd->hwq_index = hwq_index;
 
 	cmd->rcb.ctx_id = hwq->ctx_hndl;
 	cmd->rcb.msi = SISL_MSI_RRQ_UPDATED;
@@ -2654,6 +2694,74 @@ retry:
 	return count;
 }
 
+static const char *hwq_mode_name[MAX_HWQ_MODE] = { "rr", "tag", "cpu" };
+
+/**
+ * hwq_mode_show() - presents the HWQ steering mode for the host
+ * @dev:	Generic device associated with the host.
+ * @attr:	Device attribute representing the HWQ steering mode.
+ * @buf:	Buffer of length PAGE_SIZE to report back the HWQ steering mode
+ *		as a character string.
+ *
+ * Return: The size of the ASCII string returned in @buf.
+ */
+static ssize_t hwq_mode_show(struct device *dev,
+			     struct device_attribute *attr, char *buf)
+{
+	struct cxlflash_cfg *cfg = shost_priv(class_to_shost(dev));
+	struct afu *afu = cfg->afu;
+
+	return scnprintf(buf, PAGE_SIZE, "%s\n", hwq_mode_name[afu->hwq_mode]);
+}
+
+/**
+ * hwq_mode_store() - sets the HWQ steering mode for the host
+ * @dev:	Generic device associated with the host.
+ * @attr:	Device attribute representing the HWQ steering mode.
+ * @buf:	Buffer of length PAGE_SIZE containing the HWQ steering mode
+ *		as a character string.
+ * @count:	Length of data resizing in @buf.
+ *
+ * rr = Round-Robin
+ * tag = Block MQ Tagging
+ * cpu = CPU Affinity
+ *
+ * Return: The size of the ASCII string returned in @buf.
+ */
+static ssize_t hwq_mode_store(struct device *dev,
+			      struct device_attribute *attr,
+			      const char *buf, size_t count)
+{
+	struct Scsi_Host *shost = class_to_shost(dev);
+	struct cxlflash_cfg *cfg = shost_priv(shost);
+	struct device *cfgdev = &cfg->dev->dev;
+	struct afu *afu = cfg->afu;
+	int i;
+	u32 mode = MAX_HWQ_MODE;
+
+	for (i = 0; i < MAX_HWQ_MODE; i++) {
+		if (!strncmp(hwq_mode_name[i], buf, strlen(hwq_mode_name[i]))) {
+			mode = i;
+			break;
+		}
+	}
+
+	if (mode >= MAX_HWQ_MODE) {
+		dev_info(cfgdev, "Invalid HWQ steering mode.\n");
+		return -EINVAL;
+	}
+
+	if ((mode == HWQ_MODE_TAG) && !shost_use_blk_mq(shost)) {
+		dev_info(cfgdev, "SCSI-MQ is not enabled, use a different "
+			 "HWQ steering mode.\n");
+		return -EINVAL;
+	}
+
+	afu->hwq_mode = mode;
+
+	return count;
+}
+
 /**
  * mode_show() - presents the current mode of the device
  * @dev:	Generic device associated with the device.
@@ -2686,6 +2794,7 @@ static DEVICE_ATTR_RO(port2_lun_table);
 static DEVICE_ATTR_RO(port3_lun_table);
 static DEVICE_ATTR_RW(irqpoll_weight);
 static DEVICE_ATTR_RW(num_hwqs);
+static DEVICE_ATTR_RW(hwq_mode);
 
 static struct device_attribute *cxlflash_host_attrs[] = {
 	&dev_attr_port0,
@@ -2700,6 +2809,7 @@ static struct device_attribute *cxlflash_host_attrs[] = {
 	&dev_attr_port3_lun_table,
 	&dev_attr_irqpoll_weight,
 	&dev_attr_num_hwqs,
+	&dev_attr_hwq_mode,
 	NULL
 };