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SubjectRe: [PATCH]Disk IO statistics for all disks (request queue)
Hi Linus, Alan, All,

Here is a try in the direction of moving disk statistics into the
request queue. The main idea is: For each request queue,there is a
pointer to a statistics structure. The statistics structure is
dynamically allocated in blk_init_queue() and freed in
blk_cleanup_queue(). Disk statistics gathering is easier and faster now,
since less lookup is needed. In this way we extend the disk io gathering
ability, dynamically allocate statistics memory for registered device
only, and faster disk statistics gathering in the kernel side.

However, by moving statistics into the request queue, it makes
kstat_read_proc() hard (maybe slower?) to show those statistics. It is
not straightforward to find out all request queues since drivers could
have their own request queues. The method used in this patch is,for
each major, calculates the max number of disks(by the
gendisk.minor_shift), and loop around to call blk_get_queue() to lookup
the request queue associated with every disk. Any suggestions on how to
find out all request queues in kstat_read_proc()?

The fact is, the value of max number of disks calculated through
gendisk.minor_shift, may be greater than the actual max number disks
defined in the driver. For example, MAX_DRIVES defined in ide.h is 2,
but ide could have up to 4 disks in theory. ide_get_queue() returns
one of the first two request queues when the disk index is greater than
MAX_DRIVES. Thus, kstat_read_proc() will print the the statistics for
ide disk2 and disk3, since to kstat_read_proc(), there are request
queues associated with those disks(even if those disks are not exist).
I don't know whether changing the ide_get_queue() (ide_get_queue()
returns NULL if disk index is out of range) is a right way to fix this.
Could break anything? Also, any other drivers have similar issues?

One more thing I am not sure is, for the device which has multiple disks
but only use one default request queue, there is no way to differentiate
the statistics between disks; Also, gathering statistics at the
partition level seems impossible, although I am not sure how important
it is.


Attached patch is against 2.4.14. Thanks in advance for your inputs and
comments.


--
Mingming Cao
IBM Linux Technology Center
503-578-5024 IBM T/L: 775-5024
cmm@us.ibm.com
http://www.ibm.com/linux/ltcdiff -urN -X dontdiff linux-2.4.14/drivers/block/ll_rw_blk.c linux-test/drivers/block/ll_rw_blk.c
--- linux-2.4.14/drivers/block/ll_rw_blk.c Mon Oct 29 12:11:17 2001
+++ linux-test/drivers/block/ll_rw_blk.c Tue Nov 13 12:18:20 2001
@@ -183,7 +183,12 @@

if (count)
printk("blk_cleanup_queue: leaked requests (%d)\n", count);
-
+ /*
+ * free statistics structure
+ */
+ if (q->dk_stat)
+ kfree(q->dk_stat);
+
memset(q, 0, sizeof(*q));
}

@@ -393,6 +398,8 @@
**/
void blk_init_queue(request_queue_t * q, request_fn_proc * rfn)
{
+ disk_stat * new;
+
INIT_LIST_HEAD(&q->queue_head);
elevator_init(&q->elevator, ELEVATOR_LINUS);
blk_init_free_list(q);
@@ -413,6 +420,15 @@
*/
q->plug_device_fn = generic_plug_device;
q->head_active = 1;
+ /*
+ * At last, allocate and initialize the statistics
+ */
+ new = (disk_stat * )kmalloc(sizeof(disk_stat), GFP_KERNEL);
+ if (new == NULL) {
+ printk(KERN_ERR "blk_init_queue:error allocating statisitcs\n");
+ }
+ memset(new, 0, sizeof(disk_stat));
+ q->dk_stat = new;
}

#define blkdev_free_rq(list) list_entry((list)->next, struct request, queue);
@@ -497,23 +513,18 @@
else ro_bits[major][minor >> 5] &= ~(1 << (minor & 31));
}

-inline void drive_stat_acct (kdev_t dev, int rw,
+inline void drive_stat_acct (disk_stat * ds, int rw,
unsigned long nr_sectors, int new_io)
{
- unsigned int major = MAJOR(dev);
- unsigned int index;
-
- index = disk_index(dev);
- if ((index >= DK_MAX_DISK) || (major >= DK_MAX_MAJOR))
+ if (ds == NULL)
return;

- kstat.dk_drive[major][index] += new_io;
if (rw == READ) {
- kstat.dk_drive_rio[major][index] += new_io;
- kstat.dk_drive_rblk[major][index] += nr_sectors;
+ ds->dk_drive_rio += new_io;
+ ds->dk_drive_rblk += nr_sectors;
} else if (rw == WRITE) {
- kstat.dk_drive_wio[major][index] += new_io;
- kstat.dk_drive_wblk[major][index] += nr_sectors;
+ ds->dk_drive_wio += new_io;
+ ds->dk_drive_wblk += nr_sectors;
} else
printk(KERN_ERR "drive_stat_acct: cmd not R/W?\n");
}
@@ -529,7 +540,7 @@
static inline void add_request(request_queue_t * q, struct request * req,
struct list_head *insert_here)
{
- drive_stat_acct(req->rq_dev, req->cmd, req->nr_sectors, 1);
+ drive_stat_acct(q->dk_stat, req->cmd, req->nr_sectors, 1);

if (!q->plugged && q->head_active && insert_here == &q->queue_head) {
spin_unlock_irq(&io_request_lock);
@@ -701,7 +712,7 @@
req->bhtail = bh;
req->nr_sectors = req->hard_nr_sectors += count;
blk_started_io(count);
- drive_stat_acct(req->rq_dev, req->cmd, count, 0);
+ drive_stat_acct(q->dk_stat, req->cmd, count, 0);
attempt_back_merge(q, req, max_sectors, max_segments);
goto out;

@@ -716,7 +727,7 @@
req->sector = req->hard_sector = sector;
req->nr_sectors = req->hard_nr_sectors += count;
blk_started_io(count);
- drive_stat_acct(req->rq_dev, req->cmd, count, 0);
+ drive_stat_acct(q->dk_stat, req->cmd, count, 0);
attempt_front_merge(q, head, req, max_sectors, max_segments);
goto out;

diff -urN -X dontdiff linux-2.4.14/drivers/ide/ide.c linux-test/drivers/ide/ide.c
--- linux-2.4.14/drivers/ide/ide.c Thu Oct 25 13:58:35 2001
+++ linux-test/drivers/ide/ide.c Tue Nov 13 17:47:42 2001
@@ -1451,8 +1451,10 @@
request_queue_t *ide_get_queue (kdev_t dev)
{
ide_hwif_t *hwif = (ide_hwif_t *)blk_dev[MAJOR(dev)].data;
-
- return &hwif->drives[DEVICE_NR(dev) & 1].queue;
+ if (DEVICE_NR(dev) >= MAX_DRIVES)
+ return NULL;
+ else
+ return &hwif->drives[DEVICE_NR(dev)].queue;
}

/*
diff -urN -X dontdiff linux-2.4.14/drivers/md/md.c linux-test/drivers/md/md.c
--- linux-2.4.14/drivers/md/md.c Thu Oct 25 13:58:34 2001
+++ linux-test/drivers/md/md.c Tue Nov 13 17:49:31 2001
@@ -3302,12 +3302,15 @@
ITERATE_RDEV(mddev,rdev,tmp) {
int major = MAJOR(rdev->dev);
int idx = disk_index(rdev->dev);
-
+ request_queue_t * rq = blk_get_queue(rdev->dev);
+
if ((idx >= DK_MAX_DISK) || (major >= DK_MAX_MAJOR))
continue;
-
- curr_events = kstat.dk_drive_rblk[major][idx] +
- kstat.dk_drive_wblk[major][idx] ;
+
+ if (rq == NULL || (rq->dk_stat == NULL))
+ continue;
+ curr_events = rq->dk_stat->dk_drive_rblk +
+ rq->dk_stat->dk_drive_wblk ;
curr_events -= sync_io[major][idx];
if ((curr_events - rdev->last_events) > 32) {
rdev->last_events = curr_events;
diff -urN -X dontdiff linux-2.4.14/fs/proc/proc_misc.c linux-test/fs/proc/proc_misc.c
--- linux-2.4.14/fs/proc/proc_misc.c Thu Oct 11 10:46:57 2001
+++ linux-test/fs/proc/proc_misc.c Tue Nov 13 16:11:33 2001
@@ -35,12 +35,12 @@
#include <linux/module.h>
#include <linux/init.h>
#include <linux/smp_lock.h>
+#include <linux/blkdev.h>

#include <asm/uaccess.h>
#include <asm/pgtable.h>
#include <asm/io.h>

-
#define LOAD_INT(x) ((x) >> FSHIFT)
#define LOAD_FRAC(x) LOAD_INT(((x) & (FIXED_1-1)) * 100)
/*
@@ -259,7 +259,23 @@
return len;
}
#endif
-
+static inline int show_disk_stat(char * page, int len, disk_stat * ds,
+ int major, int disk)
+{
+ int active = ds->dk_drive_rio + ds->dk_drive_wio +
+ ds->dk_drive_rblk + ds->dk_drive_wblk;
+ if (active)
+ len += sprintf(page + len,
+ "(%u,%u):(%u,%u,%u,%u,%u) ",
+ major, disk,
+ ds->dk_drive_rio + ds->dk_drive_wio,
+ ds->dk_drive_rio,
+ ds->dk_drive_rblk,
+ ds->dk_drive_wio,
+ ds->dk_drive_wblk
+ );
+ return len;
+}
static int kstat_read_proc(char *page, char **start, off_t off,
int count, int *eof, void *data)
{
@@ -309,21 +325,27 @@

len += sprintf(page + len, "\ndisk_io: ");

- for (major = 0; major < DK_MAX_MAJOR; major++) {
- for (disk = 0; disk < DK_MAX_DISK; disk++) {
- int active = kstat.dk_drive[major][disk] +
- kstat.dk_drive_rblk[major][disk] +
- kstat.dk_drive_wblk[major][disk];
- if (active)
- len += sprintf(page + len,
- "(%u,%u):(%u,%u,%u,%u,%u) ",
- major, disk,
- kstat.dk_drive[major][disk],
- kstat.dk_drive_rio[major][disk],
- kstat.dk_drive_rblk[major][disk],
- kstat.dk_drive_wio[major][disk],
- kstat.dk_drive_wblk[major][disk]
- );
+ for (major = 0; major < MAX_BLKDEV; major++) {
+ disk_stat * ds;
+
+ if (!(blk_dev[major].queue)){
+ ds = (BLK_DEFAULT_QUEUE(major))->dk_stat;
+ if (ds)
+ len = show_disk_stat(page, len, ds, major, 0);
+ }else {
+ request_queue_t * q;
+ struct gendisk * hd = get_gendisk(MKDEV(major,0));
+ int max_disk = MINORMASK>>hd->minor_shift;
+
+ for (disk = 0; disk <= max_disk; disk++) {
+ q = blk_get_queue(MKDEV(major,disk<<hd->minor_shift));
+ if (!q)
+ continue;
+ ds = q->dk_stat;
+ if (!ds)
+ continue;
+ len = show_disk_stat(page, len, ds, major,disk);
+ }
}
}

diff -urN -X dontdiff linux-2.4.14/include/linux/blkdev.h linux-test/include/linux/blkdev.h
--- linux-2.4.14/include/linux/blkdev.h Mon Nov 5 12:42:57 2001
+++ linux-test/include/linux/blkdev.h Tue Nov 13 11:42:47 2001
@@ -71,6 +71,13 @@
struct list_head free;
};

+typedef struct disk_stat{
+ unsigned int dk_drive_rio;
+ unsigned int dk_drive_wio;
+ unsigned int dk_drive_rblk;
+ unsigned int dk_drive_wblk;
+} disk_stat;
+
struct request_queue
{
/*
@@ -122,6 +129,10 @@
* Tasks wait here for free request
*/
wait_queue_head_t wait_for_request;
+ /*
+ * statistics
+ */
+ disk_stat * dk_stat;
};

struct blk_dev_struct {
@@ -190,7 +201,7 @@
#define blkdev_next_request(req) blkdev_entry_to_request((req)->queue.next)
#define blkdev_prev_request(req) blkdev_entry_to_request((req)->queue.prev)

-extern void drive_stat_acct (kdev_t dev, int rw,
+extern void drive_stat_acct (disk_stat *, int rw,
unsigned long nr_sectors, int new_io);

static inline int get_hardsect_size(kdev_t dev)
diff -urN -X dontdiff linux-2.4.14/include/linux/kernel_stat.h linux-test/include/linux/kernel_stat.h
--- linux-2.4.14/include/linux/kernel_stat.h Mon Nov 5 12:42:14 2001
+++ linux-test/include/linux/kernel_stat.h Tue Nov 13 18:09:44 2001
@@ -19,11 +19,6 @@
unsigned int per_cpu_user[NR_CPUS],
per_cpu_nice[NR_CPUS],
per_cpu_system[NR_CPUS];
- unsigned int dk_drive[DK_MAX_MAJOR][DK_MAX_DISK];
- unsigned int dk_drive_rio[DK_MAX_MAJOR][DK_MAX_DISK];
- unsigned int dk_drive_wio[DK_MAX_MAJOR][DK_MAX_DISK];
- unsigned int dk_drive_rblk[DK_MAX_MAJOR][DK_MAX_DISK];
- unsigned int dk_drive_wblk[DK_MAX_MAJOR][DK_MAX_DISK];
unsigned int pgpgin, pgpgout;
unsigned int pswpin, pswpout;
#if !defined(CONFIG_ARCH_S390)
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