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scsi: cxlflash: Introduce hardware queue steering
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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>
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Matthew R. Ochs authored and Martin K. Petersen committed Apr 14, 2017
1 parent 3065267 commit 1dd0c0e
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Showing 2 changed files with 126 additions and 6 deletions.
12 changes: 11 additions & 1 deletion drivers/scsi/cxlflash/common.h
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Original file line number Diff line number Diff line change
Expand Up @@ -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.
Expand Down Expand Up @@ -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
Expand Down Expand Up @@ -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;
Expand Down
120 changes: 115 additions & 5 deletions drivers/scsi/cxlflash/main.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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.
Expand All @@ -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;
Expand All @@ -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;
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -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;
Expand Down Expand Up @@ -2654,6 +2694,74 @@ static ssize_t num_hwqs_store(struct device *dev,
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.
Expand Down Expand Up @@ -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,
Expand All @@ -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
};

Expand Down

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