st: implement tape statistics

This patch implements tape statistics in the st module via
sysfs. Current no statistics are available for tape I/O and there
is no easy way to reuse the block layer statistics for tape
as tape is a character device and does not have perform I/O in
sector sized chunks (the size of the data written to tape
can change). For tapes we also need extra stats related to
things like tape movement (via other I/O).

There have been multiple end users requesting statistics
including AT&T (and some HP customers who have not given
permission to be named). It is impossible for them
to investigate any issues related to tape performance
in a non-invasive way.

[jejb: eliminate PRId64]
Signed-off-by: Shane Seymour <shane.seymour@hp.com>
Tested-by: Shane Seymour <shane.seymour@hp.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: James Bottomley <JBottomley@Odin.com>

2 files changed, 293 insertions, 1 deletions

diff --git a/drivers/scsi/st.c b/drivers/scsi/st.c
index 9a1c34205254..3f25b8fa921d 100644
--- a/drivers/scsi/st.c
+++ b/drivers/scsi/st.c
@@ -471,6 +471,47 @@ static void st_release_request(struct st_request *streq)
 	kfree(streq);
 }
 
+static void st_do_stats(struct scsi_tape *STp, struct request *req)
+{
+	ktime_t now;
+
+	now = ktime_get();
+	if (req->cmd[0] == WRITE_6) {
+		now = ktime_sub(now, STp->stats->write_time);
+		atomic64_add(ktime_to_ns(now), &STp->stats->tot_write_time);
+		atomic64_add(ktime_to_ns(now), &STp->stats->tot_io_time);
+		atomic64_inc(&STp->stats->write_cnt);
+		if (req->errors) {
+			atomic64_add(atomic_read(&STp->stats->last_write_size)
+				- STp->buffer->cmdstat.residual,
+				&STp->stats->write_byte_cnt);
+			if (STp->buffer->cmdstat.residual > 0)
+				atomic64_inc(&STp->stats->resid_cnt);
+		} else
+			atomic64_add(atomic_read(&STp->stats->last_write_size),
+				&STp->stats->write_byte_cnt);
+	} else if (req->cmd[0] == READ_6) {
+		now = ktime_sub(now, STp->stats->read_time);
+		atomic64_add(ktime_to_ns(now), &STp->stats->tot_read_time);
+		atomic64_add(ktime_to_ns(now), &STp->stats->tot_io_time);
+		atomic64_inc(&STp->stats->read_cnt);
+		if (req->errors) {
+			atomic64_add(atomic_read(&STp->stats->last_read_size)
+				- STp->buffer->cmdstat.residual,
+				&STp->stats->read_byte_cnt);
+			if (STp->buffer->cmdstat.residual > 0)
+				atomic64_inc(&STp->stats->resid_cnt);
+		} else
+			atomic64_add(atomic_read(&STp->stats->last_read_size),
+				&STp->stats->read_byte_cnt);
+	} else {
+		now = ktime_sub(now, STp->stats->other_time);
+		atomic64_add(ktime_to_ns(now), &STp->stats->tot_io_time);
+		atomic64_inc(&STp->stats->other_cnt);
+	}
+	atomic64_dec(&STp->stats->in_flight);
+}
+
 static void st_scsi_execute_end(struct request *req, int uptodate)
 {
 	struct st_request *SRpnt = req->end_io_data;
@@ -480,6 +521,8 @@ static void st_scsi_execute_end(struct request *req, int uptodate)
 	STp->buffer->cmdstat.midlevel_result = SRpnt->result = req->errors;
 	STp->buffer->cmdstat.residual = req->resid_len;
 
+	st_do_stats(STp, req);
+
 	tmp = SRpnt->bio;
 	if (SRpnt->waiting)
 		complete(SRpnt->waiting);
@@ -496,6 +539,7 @@ static int st_scsi_execute(struct st_request *SRpnt, const unsigned char *cmd,
 	struct rq_map_data *mdata = &SRpnt->stp->buffer->map_data;
 	int err = 0;
 	int write = (data_direction == DMA_TO_DEVICE);
+	struct scsi_tape *STp = SRpnt->stp;
 
 	req = blk_get_request(SRpnt->stp->device->request_queue, write,
 			      GFP_KERNEL);
@@ -516,6 +560,17 @@ static int st_scsi_execute(struct st_request *SRpnt, const unsigned char *cmd,
 		}
 	}
 
+	atomic64_inc(&STp->stats->in_flight);
+	if (cmd[0] == WRITE_6) {
+		atomic_set(&STp->stats->last_write_size, bufflen);
+		STp->stats->write_time = ktime_get();
+	} else if (cmd[0] == READ_6) {
+		atomic_set(&STp->stats->last_read_size, bufflen);
+		STp->stats->read_time = ktime_get();
+	} else {
+		STp->stats->other_time = ktime_get();
+	}
+
 	SRpnt->bio = req->bio;
 	req->cmd_len = COMMAND_SIZE(cmd[0]);
 	memset(req->cmd, 0, BLK_MAX_CDB);
@@ -4222,6 +4277,12 @@ static int st_probe(struct device *dev)
 	}
 	tpnt->index = error;
 	sprintf(disk->disk_name, "st%d", tpnt->index);
+	tpnt->stats = kzalloc(sizeof(struct scsi_tape_stats), GFP_KERNEL);
+	if (tpnt->stats == NULL) {
+		sdev_printk(KERN_ERR, SDp,
+			    "st: Can't allocate statistics.\n");
+		goto out_idr_remove;
+	}
 
 	dev_set_drvdata(dev, tpnt);
 
@@ -4241,6 +4302,8 @@ static int st_probe(struct device *dev)
 
 out_remove_devs:
 	remove_cdevs(tpnt);
+	kfree(tpnt->stats);
+out_idr_remove:
 	spin_lock(&st_index_lock);
 	idr_remove(&st_index_idr, tpnt->index);
 	spin_unlock(&st_index_lock);
@@ -4298,6 +4361,7 @@ static void scsi_tape_release(struct kref *kref)
 
 	disk->private_data = NULL;
 	put_disk(disk);
+	kfree(tpnt->stats);
 	kfree(tpnt);
 	return;
 }
@@ -4513,6 +4577,184 @@ options_show(struct device *dev, struct device_attribute *attr, char *buf)
 }
 static DEVICE_ATTR_RO(options);
 
+/* Support for tape stats */
+
+/**
+ * read_cnt_show - return read count - count of reads made from tape drive
+ * @dev: struct device
+ * @attr: attribute structure
+ * @buf: buffer to return formatted data in
+ */
+static ssize_t read_cnt_show(struct device *dev,
+	struct device_attribute *attr, char *buf)
+{
+	struct st_modedef *STm = dev_get_drvdata(dev);
+
+	return sprintf(buf, "%lld",
+		       (long long)atomic64_read(&STm->tape->stats->read_cnt));
+}
+static DEVICE_ATTR_RO(read_cnt);
+
+/**
+ * read_byte_cnt_show - return read byte count - tape drives
+ * may use blocks less than 512 bytes this gives the raw byte count of
+ * of data read from the tape drive.
+ * @dev: struct device
+ * @attr: attribute structure
+ * @buf: buffer to return formatted data in
+ */
+static ssize_t read_byte_cnt_show(struct device *dev,
+	struct device_attribute *attr, char *buf)
+{
+	struct st_modedef *STm = dev_get_drvdata(dev);
+
+	return sprintf(buf, "%lld",
+		       (long long)atomic64_read(&STm->tape->stats->read_byte_cnt));
+}
+static DEVICE_ATTR_RO(read_byte_cnt);
+
+/**
+ * read_us_show - return read us - overall time spent waiting on reads in ns.
+ * @dev: struct device
+ * @attr: attribute structure
+ * @buf: buffer to return formatted data in
+ */
+static ssize_t read_ns_show(struct device *dev,
+	struct device_attribute *attr, char *buf)
+{
+	struct st_modedef *STm = dev_get_drvdata(dev);
+
+	return sprintf(buf, "%lld",
+		       (long long)atomic64_read(&STm->tape->stats->tot_read_time));
+}
+static DEVICE_ATTR_RO(read_ns);
+
+/**
+ * write_cnt_show - write count - number of user calls
+ * to write(2) that have written data to tape.
+ * @dev: struct device
+ * @attr: attribute structure
+ * @buf: buffer to return formatted data in
+ */
+static ssize_t write_cnt_show(struct device *dev,
+	struct device_attribute *attr, char *buf)
+{
+	struct st_modedef *STm = dev_get_drvdata(dev);
+
+	return sprintf(buf, "%lld",
+		       (long long)atomic64_read(&STm->tape->stats->write_cnt));
+}
+static DEVICE_ATTR_RO(write_cnt);
+
+/**
+ * write_byte_cnt_show - write byte count - raw count of
+ * bytes written to tape.
+ * @dev: struct device
+ * @attr: attribute structure
+ * @buf: buffer to return formatted data in
+ */
+static ssize_t write_byte_cnt_show(struct device *dev,
+	struct device_attribute *attr, char *buf)
+{
+	struct st_modedef *STm = dev_get_drvdata(dev);
+
+	return sprintf(buf, "%lld",
+		       (long long)atomic64_read(&STm->tape->stats->write_byte_cnt));
+}
+static DEVICE_ATTR_RO(write_byte_cnt);
+
+/**
+ * write_ns_show - write ns - number of nanoseconds waiting on write
+ * requests to complete.
+ * @dev: struct device
+ * @attr: attribute structure
+ * @buf: buffer to return formatted data in
+ */
+static ssize_t write_ns_show(struct device *dev,
+	struct device_attribute *attr, char *buf)
+{
+	struct st_modedef *STm = dev_get_drvdata(dev);
+
+	return sprintf(buf, "%lld",
+		       (long long)atomic64_read(&STm->tape->stats->tot_write_time));
+}
+static DEVICE_ATTR_RO(write_ns);
+
+/**
+ * in_flight_show - number of I/Os currently in flight -
+ * in most cases this will be either 0 or 1. It may be higher if someone
+ * has also issued other SCSI commands such as via an ioctl.
+ * @dev: struct device
+ * @attr: attribute structure
+ * @buf: buffer to return formatted data in
+ */
+static ssize_t in_flight_show(struct device *dev,
+	struct device_attribute *attr, char *buf)
+{
+	struct st_modedef *STm = dev_get_drvdata(dev);
+
+	return sprintf(buf, "%lld",
+		       (long long)atomic64_read(&STm->tape->stats->in_flight));
+}
+static DEVICE_ATTR_RO(in_flight);
+
+/**
+ * io_ns_show - io wait ns - this is the number of ns spent
+ * waiting on all I/O to complete. This includes tape movement commands
+ * such as rewinding, seeking to end of file or tape, it also includes
+ * read and write. To determine the time spent on tape movement
+ * subtract the read and write ns from this value.
+ * @dev: struct device
+ * @attr: attribute structure
+ * @buf: buffer to return formatted data in
+ */
+static ssize_t io_ns_show(struct device *dev,
+	struct device_attribute *attr, char *buf)
+{
+	struct st_modedef *STm = dev_get_drvdata(dev);
+
+	return sprintf(buf, "%lld",
+		       (long long)atomic64_read(&STm->tape->stats->tot_io_time));
+}
+static DEVICE_ATTR_RO(io_ns);
+
+/**
+ * other_cnt_show - other io count - this is the number of
+ * I/O requests other than read and write requests.
+ * Typically these are tape movement requests but will include driver
+ * tape movement. This includes only requests issued by the st driver.
+ * @dev: struct device
+ * @attr: attribute structure
+ * @buf: buffer to return formatted data in
+ */
+static ssize_t other_cnt_show(struct device *dev,
+	struct device_attribute *attr, char *buf)
+{
+	struct st_modedef *STm = dev_get_drvdata(dev);
+
+	return sprintf(buf, "%lld",
+		       (long long)atomic64_read(&STm->tape->stats->other_cnt));
+}
+static DEVICE_ATTR_RO(other_cnt);
+
+/**
+ * resid_cnt_show - A count of the number of times we get a residual
+ * count - this should indicate someone issuing reads larger than the
+ * block size on tape.
+ * @dev: struct device
+ * @attr: attribute structure
+ * @buf: buffer to return formatted data in
+ */
+static ssize_t resid_cnt_show(struct device *dev,
+	struct device_attribute *attr, char *buf)
+{
+	struct st_modedef *STm = dev_get_drvdata(dev);
+
+	return sprintf(buf, "%lld",
+		       (long long)atomic64_read(&STm->tape->stats->resid_cnt));
+}
+static DEVICE_ATTR_RO(resid_cnt);
+
 static struct attribute *st_dev_attrs[] = {
 	&dev_attr_defined.attr,
 	&dev_attr_default_blksize.attr,
@@ -4521,7 +4763,35 @@ static struct attribute *st_dev_attrs[] = {
 	&dev_attr_options.attr,
 	NULL,
 };
-ATTRIBUTE_GROUPS(st_dev);
+
+static struct attribute *st_stats_attrs[] = {
+	&dev_attr_read_cnt.attr,
+	&dev_attr_read_byte_cnt.attr,
+	&dev_attr_read_ns.attr,
+	&dev_attr_write_cnt.attr,
+	&dev_attr_write_byte_cnt.attr,
+	&dev_attr_write_ns.attr,
+	&dev_attr_in_flight.attr,
+	&dev_attr_io_ns.attr,
+	&dev_attr_other_cnt.attr,
+	&dev_attr_resid_cnt.attr,
+	NULL,
+};
+
+static struct attribute_group stats_group = {
+	.name = "stats",
+	.attrs = st_stats_attrs,
+};
+
+static struct attribute_group st_group = {
+	.attrs = st_dev_attrs,
+};
+
+static const struct attribute_group *st_dev_groups[] = {
+	&st_group,
+	&stats_group,
+	NULL,
+};
 
 /* The following functions may be useful for a larger audience. */
 static int sgl_map_user_pages(struct st_buffer *STbp,
diff --git a/drivers/scsi/st.h b/drivers/scsi/st.h
index f3eee0f9f40c..b6486b5d8681 100644
--- a/drivers/scsi/st.h
+++ b/drivers/scsi/st.h
@@ -92,6 +92,27 @@ struct st_partstat {
 	int drv_file;
 };
 
+/* Tape statistics */
+struct scsi_tape_stats {
+	atomic64_t read_byte_cnt;  /* bytes read */
+	atomic64_t write_byte_cnt; /* bytes written */
+	atomic64_t in_flight;      /* Number of I/Os in flight */
+	atomic64_t read_cnt;       /* Count of read requests */
+	atomic64_t write_cnt;      /* Count of write requests */
+	atomic64_t other_cnt;      /* Count of other requests either
+				    * implicit or from user space
+				    * ioctl. */
+	atomic64_t resid_cnt;      /* Count of resid_len > 0 */
+	atomic64_t tot_read_time;  /* ktime spent completing reads */
+	atomic64_t tot_write_time; /* ktime spent completing writes */
+	atomic64_t tot_io_time;    /* ktime spent doing any I/O */
+	ktime_t read_time;         /* holds ktime request was queued */
+	ktime_t write_time;        /* holds ktime request was queued */
+	ktime_t other_time;        /* holds ktime request was queued */
+	atomic_t last_read_size;   /* Number of bytes issued for last read */
+	atomic_t last_write_size;  /* Number of bytes issued for last write */
+};
+
 #define ST_NBR_PARTITIONS 4
 
 /* The tape drive descriptor */
@@ -171,6 +192,7 @@ struct scsi_tape {
 #endif
 	struct gendisk *disk;
 	struct kref     kref;
+	struct scsi_tape_stats *stats;
 };
 
 /* Bit masks for use_pf */