[S390] dasd: add enhanced DASD statistics interface

This patch extends the DASD statistics to allow for a more detailed
analysis of DASD I/O operations. In particular we want the statistics
to provide answers to the following questions:
- How many requests used a PAV alias?
- How many requests used High Performance FICON?
- How do read request perform versus write requests?

The existing DASD statistics interface has several shortcomings
- The interface for global data is a formatted text table in procfs
  (/proc/dasd/statistics). The layout is meant for human readers and
  is not to easy to parse. If values get to large for the table
  layout, they get scaled down.
- The statistics which are collected per block device can be
  accessed via an ioctl interface, which can only be extended by
  defining a new ioctl.
- There is no statistics interface for individual PAV base and alias
  devices.

To overcome theses shortcomings we create a new DASD statistics
interface in debugfs. This interface will contain one entry for global
data, one per DASD block device, and one per DASD base and alias
device. Each file contains the statistic data in easy to parse
name/value and name/array pairs. The existing interfaces will remain
functional, but they will not be extended.

Signed-off-by: Stefan Weinhuber <wein@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 531 insertions, 45 deletions

diff --git a/drivers/s390/block/dasd.c b/drivers/s390/block/dasd.c
index 86b6f1cc1b1..432444af7ee 100644
--- a/drivers/s390/block/dasd.c
+++ b/drivers/s390/block/dasd.c
@@ -22,6 +22,8 @@
 #include <linux/hdreg.h>
 #include <linux/async.h>
 #include <linux/mutex.h>
+#include <linux/debugfs.h>
+#include <linux/seq_file.h>
 
 #include <asm/ccwdev.h>
 #include <asm/ebcdic.h>
@@ -45,6 +47,7 @@
  * SECTION: exported variables of dasd.c
  */
 debug_info_t *dasd_debug_area;
+static struct dentry *dasd_debugfs_root_entry;
 struct dasd_discipline *dasd_diag_discipline_pointer;
 void dasd_int_handler(struct ccw_device *, unsigned long, struct irb *);
 
@@ -71,6 +74,8 @@ static void dasd_return_cqr_cb(struct dasd_ccw_req *, void *);
 static void dasd_device_timeout(unsigned long);
 static void dasd_block_timeout(unsigned long);
 static void __dasd_process_erp(struct dasd_device *, struct dasd_ccw_req *);
+static void dasd_profile_init(struct dasd_profile *, struct dentry *);
+static void dasd_profile_exit(struct dasd_profile *);
 
 /*
  * SECTION: Operations on the device structure.
@@ -121,7 +126,7 @@ struct dasd_device *dasd_alloc_device(void)
 	device->state = DASD_STATE_NEW;
 	device->target = DASD_STATE_NEW;
 	mutex_init(&device->state_mutex);
-
+	spin_lock_init(&device->profile.lock);
 	return device;
 }
 
@@ -159,6 +164,7 @@ struct dasd_block *dasd_alloc_block(void)
 	init_timer(&block->timer);
 	block->timer.function = dasd_block_timeout;
 	block->timer.data = (unsigned long) block;
+	spin_lock_init(&block->profile.lock);
 
 	return block;
 }
@@ -222,19 +228,44 @@ static int dasd_state_known_to_new(struct dasd_device *device)
 	return 0;
 }
 
+static struct dentry *dasd_debugfs_setup(const char *name,
+					 struct dentry *base_dentry)
+{
+	struct dentry *pde;
+
+	if (!base_dentry)
+		return NULL;
+	pde = debugfs_create_dir(name, base_dentry);
+	if (!pde || IS_ERR(pde))
+		return NULL;
+	return pde;
+}
+
 /*
  * Request the irq line for the device.
  */
 static int dasd_state_known_to_basic(struct dasd_device *device)
 {
+	struct dasd_block *block = device->block;
 	int rc;
 
 	/* Allocate and register gendisk structure. */
-	if (device->block) {
-		rc = dasd_gendisk_alloc(device->block);
+	if (block) {
+		rc = dasd_gendisk_alloc(block);
 		if (rc)
 			return rc;
-	}
+		block->debugfs_dentry =
+			dasd_debugfs_setup(block->gdp->disk_name,
+					   dasd_debugfs_root_entry);
+		dasd_profile_init(&block->profile, block->debugfs_dentry);
+		if (dasd_global_profile_level == DASD_PROFILE_ON)
+			dasd_profile_on(&device->block->profile);
+	}
+	device->debugfs_dentry =
+		dasd_debugfs_setup(dev_name(&device->cdev->dev),
+				   dasd_debugfs_root_entry);
+	dasd_profile_init(&device->profile, device->debugfs_dentry);
+
 	/* register 'device' debug area, used for all DBF_DEV_XXX calls */
 	device->debug_area = debug_register(dev_name(&device->cdev->dev), 4, 1,
 					    8 * sizeof(long));
@@ -253,6 +284,9 @@ static int dasd_state_basic_to_known(struct dasd_device *device)
 {
 	int rc;
 	if (device->block) {
+		dasd_profile_exit(&device->block->profile);
+		if (device->block->debugfs_dentry)
+			debugfs_remove(device->block->debugfs_dentry);
 		dasd_gendisk_free(device->block);
 		dasd_block_clear_timer(device->block);
 	}
@@ -260,6 +294,9 @@ static int dasd_state_basic_to_known(struct dasd_device *device)
 	if (rc)
 		return rc;
 	dasd_device_clear_timer(device);
+	dasd_profile_exit(&device->profile);
+	if (device->debugfs_dentry)
+		debugfs_remove(device->debugfs_dentry);
 
 	DBF_DEV_EVENT(DBF_EMERG, device, "%p debug area deleted", device);
 	if (device->debug_area != NULL) {
@@ -609,21 +646,13 @@ void dasd_enable_device(struct dasd_device *device)
 /*
  * SECTION: device operation (interrupt handler, start i/o, term i/o ...)
  */
-#ifdef CONFIG_DASD_PROFILE
 
-struct dasd_profile_info_t dasd_global_profile;
-unsigned int dasd_profile_level = DASD_PROFILE_OFF;
+unsigned int dasd_global_profile_level = DASD_PROFILE_OFF;
 
-/*
- * Increments counter in global and local profiling structures.
- */
-#define dasd_profile_counter(value, counter, block) \
-{ \
-	int index; \
-	for (index = 0; index < 31 && value >> (2+index); index++); \
-	dasd_global_profile.counter[index]++; \
-	block->profile.counter[index]++; \
-}
+#ifdef CONFIG_DASD_PROFILE
+struct dasd_profile_info dasd_global_profile_data;
+static struct dentry *dasd_global_profile_dentry;
+static struct dentry *dasd_debugfs_global_entry;
 
 /*
  * Add profiling information for cqr before execution.
@@ -634,30 +663,121 @@ static void dasd_profile_start(struct dasd_block *block,
 {
 	struct list_head *l;
 	unsigned int counter;
-
-	if (dasd_profile_level != DASD_PROFILE_ON)
-		return;
+	struct dasd_device *device;
 
 	/* count the length of the chanq for statistics */
 	counter = 0;
-	list_for_each(l, &block->ccw_queue)
-		if (++counter >= 31)
-			break;
-	dasd_global_profile.dasd_io_nr_req[counter]++;
-	block->profile.dasd_io_nr_req[counter]++;
+	if (dasd_global_profile_level || block->profile.data)
+		list_for_each(l, &block->ccw_queue)
+			if (++counter >= 31)
+				break;
+
+	if (dasd_global_profile_level) {
+		dasd_global_profile_data.dasd_io_nr_req[counter]++;
+		if (rq_data_dir(req) == READ)
+			dasd_global_profile_data.dasd_read_nr_req[counter]++;
+	}
+
+	spin_lock(&block->profile.lock);
+	if (block->profile.data)
+		block->profile.data->dasd_io_nr_req[counter]++;
+		if (rq_data_dir(req) == READ)
+			block->profile.data->dasd_read_nr_req[counter]++;
+	spin_unlock(&block->profile.lock);
+
+	/*
+	 * We count the request for the start device, even though it may run on
+	 * some other device due to error recovery. This way we make sure that
+	 * we count each request only once.
+	 */
+	device = cqr->startdev;
+	if (device->profile.data) {
+		counter = 1; /* request is not yet queued on the start device */
+		list_for_each(l, &device->ccw_queue)
+			if (++counter >= 31)
+				break;
+	}
+	spin_lock(&device->profile.lock);
+	if (device->profile.data) {
+		device->profile.data->dasd_io_nr_req[counter]++;
+		if (rq_data_dir(req) == READ)
+			device->profile.data->dasd_read_nr_req[counter]++;
+	}
+	spin_unlock(&device->profile.lock);
 }
 
 /*
  * Add profiling information for cqr after execution.
  */
+
+#define dasd_profile_counter(value, index)			   \
+{								   \
+	for (index = 0; index < 31 && value >> (2+index); index++) \
+		;						   \
+}
+
+static void dasd_profile_end_add_data(struct dasd_profile_info *data,
+				      int is_alias,
+				      int is_tpm,
+				      int is_read,
+				      long sectors,
+				      int sectors_ind,
+				      int tottime_ind,
+				      int tottimeps_ind,
+				      int strtime_ind,
+				      int irqtime_ind,
+				      int irqtimeps_ind,
+				      int endtime_ind)
+{
+	/* in case of an overflow, reset the whole profile */
+	if (data->dasd_io_reqs == UINT_MAX) {
+			memset(data, 0, sizeof(*data));
+			getnstimeofday(&data->starttod);
+	}
+	data->dasd_io_reqs++;
+	data->dasd_io_sects += sectors;
+	if (is_alias)
+		data->dasd_io_alias++;
+	if (is_tpm)
+		data->dasd_io_tpm++;
+
+	data->dasd_io_secs[sectors_ind]++;
+	data->dasd_io_times[tottime_ind]++;
+	data->dasd_io_timps[tottimeps_ind]++;
+	data->dasd_io_time1[strtime_ind]++;
+	data->dasd_io_time2[irqtime_ind]++;
+	data->dasd_io_time2ps[irqtimeps_ind]++;
+	data->dasd_io_time3[endtime_ind]++;
+
+	if (is_read) {
+		data->dasd_read_reqs++;
+		data->dasd_read_sects += sectors;
+		if (is_alias)
+			data->dasd_read_alias++;
+		if (is_tpm)
+			data->dasd_read_tpm++;
+		data->dasd_read_secs[sectors_ind]++;
+		data->dasd_read_times[tottime_ind]++;
+		data->dasd_read_time1[strtime_ind]++;
+		data->dasd_read_time2[irqtime_ind]++;
+		data->dasd_read_time3[endtime_ind]++;
+	}
+}
+
 static void dasd_profile_end(struct dasd_block *block,
 			     struct dasd_ccw_req *cqr,
 			     struct request *req)
 {
 	long strtime, irqtime, endtime, tottime;	/* in microseconds */
 	long tottimeps, sectors;
+	struct dasd_device *device;
+	int sectors_ind, tottime_ind, tottimeps_ind, strtime_ind;
+	int irqtime_ind, irqtimeps_ind, endtime_ind;
 
-	if (dasd_profile_level != DASD_PROFILE_ON)
+	device = cqr->startdev;
+	if (!(dasd_global_profile_level ||
+	      block->profile.data ||
+	      device->profile.data))
 		return;
 
 	sectors = blk_rq_sectors(req);
@@ -672,29 +792,392 @@ static void dasd_profile_end(struct dasd_block *block,
 	tottime = ((cqr->endclk - cqr->buildclk) >> 12);
 	tottimeps = tottime / sectors;
 
-	if (!dasd_global_profile.dasd_io_reqs)
-		memset(&dasd_global_profile, 0,
-		       sizeof(struct dasd_profile_info_t));
-	dasd_global_profile.dasd_io_reqs++;
-	dasd_global_profile.dasd_io_sects += sectors;
-
-	if (!block->profile.dasd_io_reqs)
-		memset(&block->profile, 0,
-		       sizeof(struct dasd_profile_info_t));
-	block->profile.dasd_io_reqs++;
-	block->profile.dasd_io_sects += sectors;
-
-	dasd_profile_counter(sectors, dasd_io_secs, block);
-	dasd_profile_counter(tottime, dasd_io_times, block);
-	dasd_profile_counter(tottimeps, dasd_io_timps, block);
-	dasd_profile_counter(strtime, dasd_io_time1, block);
-	dasd_profile_counter(irqtime, dasd_io_time2, block);
-	dasd_profile_counter(irqtime / sectors, dasd_io_time2ps, block);
-	dasd_profile_counter(endtime, dasd_io_time3, block);
+	dasd_profile_counter(sectors, sectors_ind);
+	dasd_profile_counter(tottime, tottime_ind);
+	dasd_profile_counter(tottimeps, tottimeps_ind);
+	dasd_profile_counter(strtime, strtime_ind);
+	dasd_profile_counter(irqtime, irqtime_ind);
+	dasd_profile_counter(irqtime / sectors, irqtimeps_ind);
+	dasd_profile_counter(endtime, endtime_ind);
+
+	if (dasd_global_profile_level) {
+		dasd_profile_end_add_data(&dasd_global_profile_data,
+					  cqr->startdev != block->base,
+					  cqr->cpmode == 1,
+					  rq_data_dir(req) == READ,
+					  sectors, sectors_ind, tottime_ind,
+					  tottimeps_ind, strtime_ind,
+					  irqtime_ind, irqtimeps_ind,
+					  endtime_ind);
+	}
+
+	spin_lock(&block->profile.lock);
+	if (block->profile.data)
+		dasd_profile_end_add_data(block->profile.data,
+					  cqr->startdev != block->base,
+					  cqr->cpmode == 1,
+					  rq_data_dir(req) == READ,
+					  sectors, sectors_ind, tottime_ind,
+					  tottimeps_ind, strtime_ind,
+					  irqtime_ind, irqtimeps_ind,
+					  endtime_ind);
+	spin_unlock(&block->profile.lock);
+
+	spin_lock(&device->profile.lock);
+	if (device->profile.data)
+		dasd_profile_end_add_data(device->profile.data,
+					  cqr->startdev != block->base,
+					  cqr->cpmode == 1,
+					  rq_data_dir(req) == READ,
+					  sectors, sectors_ind, tottime_ind,
+					  tottimeps_ind, strtime_ind,
+					  irqtime_ind, irqtimeps_ind,
+					  endtime_ind);
+	spin_unlock(&device->profile.lock);
+}
+
+void dasd_profile_reset(struct dasd_profile *profile)
+{
+	struct dasd_profile_info *data;
+
+	spin_lock_bh(&profile->lock);
+	data = profile->data;
+	if (!data) {
+		spin_unlock_bh(&profile->lock);
+		return;
+	}
+	memset(data, 0, sizeof(*data));
+	getnstimeofday(&data->starttod);
+	spin_unlock_bh(&profile->lock);
+}
+
+void dasd_global_profile_reset(void)
+{
+	memset(&dasd_global_profile_data, 0, sizeof(dasd_global_profile_data));
+	getnstimeofday(&dasd_global_profile_data.starttod);
+}
+
+int dasd_profile_on(struct dasd_profile *profile)
+{
+	struct dasd_profile_info *data;
+
+	data = kzalloc(sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+	spin_lock_bh(&profile->lock);
+	if (profile->data) {
+		spin_unlock_bh(&profile->lock);
+		kfree(data);
+		return 0;
+	}
+	getnstimeofday(&data->starttod);
+	profile->data = data;
+	spin_unlock_bh(&profile->lock);
+	return 0;
+}
+
+void dasd_profile_off(struct dasd_profile *profile)
+{
+	spin_lock_bh(&profile->lock);
+	kfree(profile->data);
+	profile->data = NULL;
+	spin_unlock_bh(&profile->lock);
+}
+
+char *dasd_get_user_string(const char __user *user_buf, size_t user_len)
+{
+	char *buffer;
+
+	buffer = kmalloc(user_len + 1, GFP_KERNEL);
+	if (buffer == NULL)
+		return ERR_PTR(-ENOMEM);
+	if (copy_from_user(buffer, user_buf, user_len) != 0) {
+		kfree(buffer);
+		return ERR_PTR(-EFAULT);
+	}
+	/* got the string, now strip linefeed. */
+	if (buffer[user_len - 1] == '\n')
+		buffer[user_len - 1] = 0;
+	else
+		buffer[user_len] = 0;
+	return buffer;
 }
+
+static ssize_t dasd_stats_write(struct file *file,
+				const char __user *user_buf,
+				size_t user_len, loff_t *pos)
+{
+	char *buffer, *str;
+	int rc;
+	struct seq_file *m = (struct seq_file *)file->private_data;
+	struct dasd_profile *prof = m->private;
+
+	if (user_len > 65536)
+		user_len = 65536;
+	buffer = dasd_get_user_string(user_buf, user_len);
+	if (IS_ERR(buffer))
+		return PTR_ERR(buffer);
+
+	str = skip_spaces(buffer);
+	rc = user_len;
+	if (strncmp(str, "reset", 5) == 0) {
+		dasd_profile_reset(prof);
+	} else if (strncmp(str, "on", 2) == 0) {
+		rc = dasd_profile_on(prof);
+		if (!rc)
+			rc = user_len;
+	} else if (strncmp(str, "off", 3) == 0) {
+		dasd_profile_off(prof);
+	} else
+		rc = -EINVAL;
+	kfree(buffer);
+	return rc;
+}
+
+static void dasd_stats_array(struct seq_file *m, unsigned int *array)
+{
+	int i;
+
+	for (i = 0; i < 32; i++)
+		seq_printf(m, "%u ", array[i]);
+	seq_putc(m, '\n');
+}
+
+static void dasd_stats_seq_print(struct seq_file *m,
+				 struct dasd_profile_info *data)
+{
+	seq_printf(m, "start_time %ld.%09ld\n",
+		   data->starttod.tv_sec, data->starttod.tv_nsec);
+	seq_printf(m, "total_requests %u\n", data->dasd_io_reqs);
+	seq_printf(m, "total_sectors %u\n", data->dasd_io_sects);
+	seq_printf(m, "total_pav %u\n", data->dasd_io_alias);
+	seq_printf(m, "total_hpf %u\n", data->dasd_io_tpm);
+	seq_printf(m, "histogram_sectors ");
+	dasd_stats_array(m, data->dasd_io_secs);
+	seq_printf(m, "histogram_io_times ");
+	dasd_stats_array(m, data->dasd_io_times);
+	seq_printf(m, "histogram_io_times_weighted ");
+	dasd_stats_array(m, data->dasd_io_timps);
+	seq_printf(m, "histogram_time_build_to_ssch ");
+	dasd_stats_array(m, data->dasd_io_time1);
+	seq_printf(m, "histogram_time_ssch_to_irq ");
+	dasd_stats_array(m, data->dasd_io_time2);
+	seq_printf(m, "histogram_time_ssch_to_irq_weighted ");
+	dasd_stats_array(m, data->dasd_io_time2ps);
+	seq_printf(m, "histogram_time_irq_to_end ");
+	dasd_stats_array(m, data->dasd_io_time3);
+	seq_printf(m, "histogram_ccw_queue_length ");
+	dasd_stats_array(m, data->dasd_io_nr_req);
+	seq_printf(m, "total_read_requests %u\n", data->dasd_read_reqs);
+	seq_printf(m, "total_read_sectors %u\n", data->dasd_read_sects);
+	seq_printf(m, "total_read_pav %u\n", data->dasd_read_alias);
+	seq_printf(m, "total_read_hpf %u\n", data->dasd_read_tpm);
+	seq_printf(m, "histogram_read_sectors ");
+	dasd_stats_array(m, data->dasd_read_secs);
+	seq_printf(m, "histogram_read_times ");
+	dasd_stats_array(m, data->dasd_read_times);
+	seq_printf(m, "histogram_read_time_build_to_ssch ");
+	dasd_stats_array(m, data->dasd_read_time1);
+	seq_printf(m, "histogram_read_time_ssch_to_irq ");
+	dasd_stats_array(m, data->dasd_read_time2);
+	seq_printf(m, "histogram_read_time_irq_to_end ");
+	dasd_stats_array(m, data->dasd_read_time3);
+	seq_printf(m, "histogram_read_ccw_queue_length ");
+	dasd_stats_array(m, data->dasd_read_nr_req);
+}
+
+static int dasd_stats_show(struct seq_file *m, void *v)
+{
+	struct dasd_profile *profile;
+	struct dasd_profile_info *data;
+
+	profile = m->private;
+	spin_lock_bh(&profile->lock);
+	data = profile->data;
+	if (!data) {
+		spin_unlock_bh(&profile->lock);
+		seq_printf(m, "disabled\n");
+		return 0;
+	}
+	dasd_stats_seq_print(m, data);
+	spin_unlock_bh(&profile->lock);
+	return 0;
+}
+
+static int dasd_stats_open(struct inode *inode, struct file *file)
+{
+	struct dasd_profile *profile = inode->i_private;
+	return single_open(file, dasd_stats_show, profile);
+}
+
+static const struct file_operations dasd_stats_raw_fops = {
+	.owner		= THIS_MODULE,
+	.open		= dasd_stats_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+	.write		= dasd_stats_write,
+};
+
+static ssize_t dasd_stats_global_write(struct file *file,
+				       const char __user *user_buf,
+				       size_t user_len, loff_t *pos)
+{
+	char *buffer, *str;
+	ssize_t rc;
+
+	if (user_len > 65536)
+		user_len = 65536;
+	buffer = dasd_get_user_string(user_buf, user_len);
+	if (IS_ERR(buffer))
+		return PTR_ERR(buffer);
+	str = skip_spaces(buffer);
+	rc = user_len;
+	if (strncmp(str, "reset", 5) == 0) {
+		dasd_global_profile_reset();
+	} else if (strncmp(str, "on", 2) == 0) {
+		dasd_global_profile_reset();
+		dasd_global_profile_level = DASD_PROFILE_GLOBAL_ONLY;
+	} else if (strncmp(str, "off", 3) == 0) {
+		dasd_global_profile_level = DASD_PROFILE_OFF;
+	} else
+		rc = -EINVAL;
+	kfree(buffer);
+	return rc;
+}
+
+static int dasd_stats_global_show(struct seq_file *m, void *v)
+{
+	if (!dasd_global_profile_level) {
+		seq_printf(m, "disabled\n");
+		return 0;
+	}
+	dasd_stats_seq_print(m, &dasd_global_profile_data);
+	return 0;
+}
+
+static int dasd_stats_global_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, dasd_stats_global_show, NULL);
+}
+
+static const struct file_operations dasd_stats_global_fops = {
+	.owner		= THIS_MODULE,
+	.open		= dasd_stats_global_open,
+	.read		= seq_read,
+	.llseek		= seq_lseek,
+	.release	= single_release,
+	.write		= dasd_stats_global_write,
+};
+
+static void dasd_profile_init(struct dasd_profile *profile,
+			      struct dentry *base_dentry)
+{
+	mode_t mode;
+	struct dentry *pde;
+
+	if (!base_dentry)
+		return;
+	profile->dentry = NULL;
+	profile->data = NULL;
+	mode = (S_IRUSR | S_IWUSR | S_IFREG);
+	pde = debugfs_create_file("statistics", mode, base_dentry,
+				  profile, &dasd_stats_raw_fops);
+	if (pde && !IS_ERR(pde))
+		profile->dentry = pde;
+	return;
+}
+
+static void dasd_profile_exit(struct dasd_profile *profile)
+{
+	dasd_profile_off(profile);
+	if (profile->dentry) {
+		debugfs_remove(profile->dentry);
+		profile->dentry = NULL;
+	}
+}
+
+static void dasd_statistics_removeroot(void)
+{
+	dasd_global_profile_level = DASD_PROFILE_OFF;
+	if (dasd_global_profile_dentry) {
+		debugfs_remove(dasd_global_profile_dentry);
+		dasd_global_profile_dentry = NULL;
+	}
+	if (dasd_debugfs_global_entry)
+		debugfs_remove(dasd_debugfs_global_entry);
+	if (dasd_debugfs_root_entry)
+		debugfs_remove(dasd_debugfs_root_entry);
+}
+
+static void dasd_statistics_createroot(void)
+{
+	mode_t mode;
+	struct dentry *pde;
+
+	dasd_debugfs_root_entry = NULL;
+	dasd_debugfs_global_entry = NULL;
+	dasd_global_profile_dentry = NULL;
+	pde = debugfs_create_dir("dasd", NULL);
+	if (!pde || IS_ERR(pde))
+		goto error;
+	dasd_debugfs_root_entry = pde;
+	pde = debugfs_create_dir("global", dasd_debugfs_root_entry);
+	if (!pde || IS_ERR(pde))
+		goto error;
+	dasd_debugfs_global_entry = pde;
+
+	mode = (S_IRUSR | S_IWUSR | S_IFREG);
+	pde = debugfs_create_file("statistics", mode, dasd_debugfs_global_entry,
+				  NULL, &dasd_stats_global_fops);
+	if (!pde || IS_ERR(pde))
+		goto error;
+	dasd_global_profile_dentry = pde;
+	return;
+
+error:
+	DBF_EVENT(DBF_ERR, "%s",
+		  "Creation of the dasd debugfs interface failed");
+	dasd_statistics_removeroot();
+	return;
+}
+
 #else
 #define dasd_profile_start(block, cqr, req) do {} while (0)
 #define dasd_profile_end(block, cqr, req) do {} while (0)
+
+static void dasd_statistics_createroot(void)
+{
+	return;
+}
+
+static void dasd_statistics_removeroot(void)
+{
+	return;
+}
+
+int dasd_stats_generic_show(struct seq_file *m, void *v)
+{
+	seq_printf(m, "Statistics are not activated in this kernel\n");
+	return 0;
+}
+
+static void dasd_profile_init(struct dasd_profile *profile,
+			      struct dentry *base_dentry)
+{
+	return;
+}
+
+static void dasd_profile_exit(struct dasd_profile *profile)
+{
+	return;
+}
+
+int dasd_profile_on(struct dasd_profile *profile)
+{
+	return 0;
+}
+
 #endif				/* CONFIG_DASD_PROFILE */
 
 /*
@@ -2441,6 +2924,7 @@ dasd_exit(void)
 		debug_unregister(dasd_debug_area);
 		dasd_debug_area = NULL;
 	}
+	dasd_statistics_removeroot();
 }
 
 /*
@@ -2992,6 +3476,8 @@ static int __init dasd_init(void)
 
 	dasd_diag_discipline_pointer = NULL;
 
+	dasd_statistics_createroot();
+
 	rc = dasd_devmap_init();
 	if (rc)
 		goto failed;