[PATCH v3 4/4] scsi: use percpu counters for iostat counters in struct scsi_device

[Sumit Saxena <sumit.saxena@broadcom.com>]

iorequest_cnt and iodone_cnt are updated on every command dispatch and
completion, often from different CPUs on high queue depth workloads.
Using adjacent atomic_t fields causes cache line contention between the
submission and completion paths.

Extend the same treatment to ioerr_cnt and iotmo_cnt so all four iostat
counters in struct scsi_device use struct percpu_counter.

Suggested-by: John Garry <john.g.garry@oracle.com>
Signed-off-by: Sumit Saxena <sumit.saxena@broadcom.com>
---
 drivers/scsi/scsi_error.c  |  4 ++--
 drivers/scsi/scsi_lib.c    | 10 +++++-----
 drivers/scsi/scsi_scan.c   |  8 ++++++++
 drivers/scsi/scsi_sysfs.c  | 23 ++++++++++++++---------
 drivers/scsi/sd.c          |  2 +-
 include/scsi/scsi_device.h |  9 +++++----
 6 files changed, 35 insertions(+), 21 deletions(-)

diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c
index 147127fb4db9..b1aa7da2ba7c 100644
--- a/drivers/scsi/scsi_error.c
+++ b/drivers/scsi/scsi_error.c
@@ -349,7 +349,7 @@ enum blk_eh_timer_return scsi_timeout(struct request *req)
 	trace_scsi_dispatch_cmd_timeout(scmd);
 	scsi_log_completion(scmd, TIMEOUT_ERROR);
 
-	atomic_inc(&scmd->device->iotmo_cnt);
+	percpu_counter_inc(&scmd->device->iotmo_cnt);
 	if (host->eh_deadline != -1 && !host->last_reset)
 		host->last_reset = jiffies;
 
@@ -370,7 +370,7 @@ enum blk_eh_timer_return scsi_timeout(struct request *req)
 	 */
 	if (test_and_set_bit(SCMD_STATE_COMPLETE, &scmd->state))
 		return BLK_EH_DONE;
-	atomic_inc(&scmd->device->iodone_cnt);
+	percpu_counter_inc(&scmd->device->iodone_cnt);
 	if (scsi_abort_command(scmd) != SUCCESS) {
 		set_host_byte(scmd, DID_TIME_OUT);
 		scsi_eh_scmd_add(scmd);
diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 6e8c7a42603e..979fdace33ac 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -1554,9 +1554,9 @@ static void scsi_complete(struct request *rq)
 
 	INIT_LIST_HEAD(&cmd->eh_entry);
 
-	atomic_inc(&cmd->device->iodone_cnt);
+	percpu_counter_inc(&cmd->device->iodone_cnt);
 	if (cmd->result)
-		atomic_inc(&cmd->device->ioerr_cnt);
+		percpu_counter_inc(&cmd->device->ioerr_cnt);
 
 	disposition = scsi_decide_disposition(cmd);
 	if (disposition != SUCCESS && scsi_cmd_runtime_exceeced(cmd))
@@ -1592,7 +1592,7 @@ static enum scsi_qc_status scsi_dispatch_cmd(struct scsi_cmnd *cmd)
 	struct Scsi_Host *host = cmd->device->host;
 	int rtn = 0;
 
-	atomic_inc(&cmd->device->iorequest_cnt);
+	percpu_counter_inc(&cmd->device->iorequest_cnt);
 
 	/* check if the device is still usable */
 	if (unlikely(cmd->device->sdev_state == SDEV_DEL)) {
@@ -1614,7 +1614,7 @@ static enum scsi_qc_status scsi_dispatch_cmd(struct scsi_cmnd *cmd)
 		 */
 		SCSI_LOG_MLQUEUE(3, scmd_printk(KERN_INFO, cmd,
 			"queuecommand : device blocked\n"));
-		atomic_dec(&cmd->device->iorequest_cnt);
+		percpu_counter_dec(&cmd->device->iorequest_cnt);
 		return SCSI_MLQUEUE_DEVICE_BUSY;
 	}
 
@@ -1647,7 +1647,7 @@ static enum scsi_qc_status scsi_dispatch_cmd(struct scsi_cmnd *cmd)
 	trace_scsi_dispatch_cmd_start(cmd);
 	rtn = host->hostt->queuecommand(host, cmd);
 	if (rtn) {
-		atomic_dec(&cmd->device->iorequest_cnt);
+		percpu_counter_dec(&cmd->device->iorequest_cnt);
 		trace_scsi_dispatch_cmd_error(cmd, rtn);
 		if (rtn != SCSI_MLQUEUE_DEVICE_BUSY &&
 		    rtn != SCSI_MLQUEUE_TARGET_BUSY)
diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
index 121a14d5fdb8..bc885c72f01e 100644
--- a/drivers/scsi/scsi_scan.c
+++ b/drivers/scsi/scsi_scan.c
@@ -350,6 +350,14 @@ static struct scsi_device *scsi_alloc_sdev(struct scsi_target *starget,
 
 	scsi_sysfs_device_initialize(sdev);
 
+	if (percpu_counter_init(&sdev->iorequest_cnt, 0, GFP_KERNEL) ||
+	    percpu_counter_init(&sdev->iodone_cnt, 0, GFP_KERNEL) ||
+	    percpu_counter_init(&sdev->ioerr_cnt, 0, GFP_KERNEL) ||
+	    percpu_counter_init(&sdev->iotmo_cnt, 0, GFP_KERNEL)) {
+		ret = -ENOMEM;
+		goto out_device_destroy;
+	}
+
 	if (scsi_device_is_pseudo_dev(sdev))
 		return sdev;
 
diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
index dfc3559e7e04..f652edd16497 100644
--- a/drivers/scsi/scsi_sysfs.c
+++ b/drivers/scsi/scsi_sysfs.c
@@ -516,6 +516,10 @@ static void scsi_device_dev_release(struct device *dev)
 	if (vpd_pgb7)
 		kfree_rcu(vpd_pgb7, rcu);
 	kfree(sdev->inquiry);
+	percpu_counter_destroy(&sdev->iotmo_cnt);
+	percpu_counter_destroy(&sdev->ioerr_cnt);
+	percpu_counter_destroy(&sdev->iodone_cnt);
+	percpu_counter_destroy(&sdev->iorequest_cnt);
 	kfree(sdev);
 
 	if (parent)
@@ -936,26 +940,27 @@ static ssize_t
 show_iostat_counterbits(struct device *dev, struct device_attribute *attr,
 			char *buf)
 {
-	return snprintf(buf, 20, "%d\n", (int)sizeof(atomic_t) * 8);
+	/* iostat counters are per-CPU sums (s64).  Report width for tools. */
+	return sysfs_emit(buf, "%zu\n", sizeof(s64) * 8);
 }
 
 static DEVICE_ATTR(iocounterbits, S_IRUGO, show_iostat_counterbits, NULL);
 
-#define show_sdev_iostat(field)						\
+#define show_sdev_iostat_percpu(field)					\
 static ssize_t								\
 show_iostat_##field(struct device *dev, struct device_attribute *attr,	\
 		    char *buf)						\
 {									\
 	struct scsi_device *sdev = to_scsi_device(dev);			\
-	unsigned long long count = atomic_read(&sdev->field);		\
-	return snprintf(buf, 20, "0x%llx\n", count);			\
+	unsigned long long count = percpu_counter_sum(&sdev->field);	\
+	return sysfs_emit(buf, "0x%llx\n", count);			\
 }									\
-static DEVICE_ATTR(field, S_IRUGO, show_iostat_##field, NULL)
+static DEVICE_ATTR(field, 0444, show_iostat_##field, NULL)
 
-show_sdev_iostat(iorequest_cnt);
-show_sdev_iostat(iodone_cnt);
-show_sdev_iostat(ioerr_cnt);
-show_sdev_iostat(iotmo_cnt);
+show_sdev_iostat_percpu(iorequest_cnt);
+show_sdev_iostat_percpu(iodone_cnt);
+show_sdev_iostat_percpu(ioerr_cnt);
+show_sdev_iostat_percpu(iotmo_cnt);
 
 static ssize_t
 sdev_show_modalias(struct device *dev, struct device_attribute *attr, char *buf)
diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c
index adc3fa55ca2c..b7ce01de17b3 100644
--- a/drivers/scsi/sd.c
+++ b/drivers/scsi/sd.c
@@ -4043,7 +4043,7 @@ static int sd_probe(struct scsi_device *sdp)
 	sdkp->index = index;
 	sdkp->max_retries = SD_MAX_RETRIES;
 	atomic_set(&sdkp->openers, 0);
-	atomic_set(&sdkp->device->ioerr_cnt, 0);
+	percpu_counter_set(&sdkp->device->ioerr_cnt, 0);
 
 	if (!sdp->request_queue->rq_timeout) {
 		if (sdp->type != TYPE_MOD)
diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h
index 029f5115b2ea..4be36bf2a475 100644
--- a/include/scsi/scsi_device.h
+++ b/include/scsi/scsi_device.h
@@ -9,6 +9,7 @@
 #include <scsi/scsi.h>
 #include <scsi/scsi_common.h>
 #include <linux/atomic.h>
+#include <linux/percpu_counter.h>
 #include <linux/sbitmap.h>
 
 struct bsg_device;
@@ -272,10 +273,10 @@ struct scsi_device {
 	unsigned int max_device_blocked; /* what device_blocked counts down from  */
 #define SCSI_DEFAULT_DEVICE_BLOCKED	3
 
-	atomic_t iorequest_cnt;
-	atomic_t iodone_cnt;
-	atomic_t ioerr_cnt;
-	atomic_t iotmo_cnt;
+	struct percpu_counter iorequest_cnt;
+	struct percpu_counter iodone_cnt;
+	struct percpu_counter ioerr_cnt;
+	struct percpu_counter iotmo_cnt;
 
 	struct device		sdev_gendev,
 				sdev_dev;
-- 
2.43.7