* [PATCH 1/3] dm-mpath: interface change for dynamic load balancers
2009-03-18 8:34 Subject: [PATCH 0/3] dm-mpath: dynamic load balancers (v1) Kiyoshi Ueda
@ 2009-03-18 8:38 ` Kiyoshi Ueda
2009-03-18 8:39 ` [PATCH 2/3] dm-mpath: add queue-length oriented dynamic load balancer Kiyoshi Ueda
2009-03-18 8:40 ` [PATCH 3/3] dm-mpath: add service-time " Kiyoshi Ueda
2 siblings, 0 replies; 4+ messages in thread
From: Kiyoshi Ueda @ 2009-03-18 8:38 UTC (permalink / raw)
To: Alasdair Kergon; +Cc: device-mapper development, stefan.bader
This patch changes the dm path selector interface for dynamic
load balancers:
o adding a new hook, start_io()
o adding 'nr_bytes' parameter to select_path()/start_io()/end_io()
to pass the size of the I/O
start_io() is called when a target driver actually submits I/O
to the selected path.
Path selectors can use it to start accounting of the I/O.
(e.g. counting the number of in-flight I/Os.)
The start_io hook is based on the patch posted by Stefan Bader:
https://www.redhat.com/archives/dm-devel/2005-October/msg00050.html
nr_bytes, the size of the I/O, is used by path selectors for
size-based decision.
dm-service-time uses it to estimate service time, for example.
(Added the nr_bytes member to dm_mpath_io instead of using existing
details.bi_size, since request-based dm patch deletes it.)
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Cc: Vijayakumar Balasubramanian <vijayakumar@hp.com>
Cc: Alasdair G Kergon <agk@redhat.com>
---
drivers/md/dm-mpath.c | 28 ++++++++++++++++++----------
drivers/md/dm-path-selector.h | 8 ++++++--
drivers/md/dm-round-robin.c | 2 +-
3 files changed, 25 insertions(+), 13 deletions(-)
Index: 2.6.29-rc8/drivers/md/dm-mpath.c
===================================================================
--- 2.6.29-rc8.orig/drivers/md/dm-mpath.c
+++ 2.6.29-rc8/drivers/md/dm-mpath.c
@@ -103,6 +103,7 @@ struct multipath {
struct dm_mpath_io {
struct pgpath *pgpath;
struct dm_bio_details details;
+ size_t nr_bytes;
};
typedef int (*action_fn) (struct pgpath *pgpath);
@@ -251,11 +252,12 @@ static void __switch_pg(struct multipath
m->pg_init_count = 0;
}
-static int __choose_path_in_pg(struct multipath *m, struct priority_group *pg)
+static int __choose_path_in_pg(struct multipath *m, struct priority_group *pg,
+ size_t nr_bytes)
{
struct dm_path *path;
- path = pg->ps.type->select_path(&pg->ps, &m->repeat_count);
+ path = pg->ps.type->select_path(&pg->ps, &m->repeat_count, nr_bytes);
if (!path)
return -ENXIO;
@@ -267,7 +269,7 @@ static int __choose_path_in_pg(struct mu
return 0;
}
-static void __choose_pgpath(struct multipath *m)
+static void __choose_pgpath(struct multipath *m, size_t nr_bytes)
{
struct priority_group *pg;
unsigned bypassed = 1;
@@ -279,12 +281,12 @@ static void __choose_pgpath(struct multi
if (m->next_pg) {
pg = m->next_pg;
m->next_pg = NULL;
- if (!__choose_path_in_pg(m, pg))
+ if (!__choose_path_in_pg(m, pg, nr_bytes))
return;
}
/* Don't change PG until it has no remaining paths */
- if (m->current_pg && !__choose_path_in_pg(m, m->current_pg))
+ if (m->current_pg && !__choose_path_in_pg(m, m->current_pg, nr_bytes))
return;
/*
@@ -296,7 +298,7 @@ static void __choose_pgpath(struct multi
list_for_each_entry(pg, &m->priority_groups, list) {
if (pg->bypassed == bypassed)
continue;
- if (!__choose_path_in_pg(m, pg))
+ if (!__choose_path_in_pg(m, pg, nr_bytes))
return;
}
} while (bypassed--);
@@ -327,6 +329,7 @@ static int map_io(struct multipath *m, s
struct dm_mpath_io *mpio, unsigned was_queued)
{
int r = DM_MAPIO_REMAPPED;
+ size_t nr_bytes = bio->bi_size;
unsigned long flags;
struct pgpath *pgpath;
@@ -335,7 +338,7 @@ static int map_io(struct multipath *m, s
/* Do we need to select a new pgpath? */
if (!m->current_pgpath ||
(!m->queue_io && (m->repeat_count && --m->repeat_count == 0)))
- __choose_pgpath(m);
+ __choose_pgpath(m, nr_bytes);
pgpath = m->current_pgpath;
@@ -360,6 +363,11 @@ static int map_io(struct multipath *m, s
r = -EIO; /* Failed */
mpio->pgpath = pgpath;
+ mpio->nr_bytes = nr_bytes;
+
+ if (r == DM_MAPIO_REMAPPED && pgpath->pg->ps.type->start_io)
+ pgpath->pg->ps.type->start_io(&pgpath->pg->ps, &pgpath->path,
+ nr_bytes);
spin_unlock_irqrestore(&m->lock, flags);
@@ -438,7 +446,7 @@ static void process_queued_ios(struct wo
goto out;
if (!m->current_pgpath)
- __choose_pgpath(m);
+ __choose_pgpath(m, 0);
pgpath = m->current_pgpath;
@@ -1196,7 +1204,7 @@ static int multipath_end_io(struct dm_ta
if (pgpath) {
ps = &pgpath->pg->ps;
if (ps->type->end_io)
- ps->type->end_io(ps, &pgpath->path);
+ ps->type->end_io(ps, &pgpath->path, mpio->nr_bytes);
}
if (r != DM_ENDIO_INCOMPLETE)
mempool_free(mpio, m->mpio_pool);
@@ -1412,7 +1420,7 @@ static int multipath_ioctl(struct dm_tar
spin_lock_irqsave(&m->lock, flags);
if (!m->current_pgpath)
- __choose_pgpath(m);
+ __choose_pgpath(m, 0);
if (m->current_pgpath) {
bdev = m->current_pgpath->path.dev->bdev;
Index: 2.6.29-rc8/drivers/md/dm-path-selector.h
===================================================================
--- 2.6.29-rc8.orig/drivers/md/dm-path-selector.h
+++ 2.6.29-rc8/drivers/md/dm-path-selector.h
@@ -56,7 +56,8 @@ struct path_selector_type {
* the path fails.
*/
struct dm_path *(*select_path) (struct path_selector *ps,
- unsigned *repeat_count);
+ unsigned *repeat_count,
+ size_t nr_bytes);
/*
* Notify the selector that a path has failed.
@@ -75,7 +76,10 @@ struct path_selector_type {
int (*status) (struct path_selector *ps, struct dm_path *path,
status_type_t type, char *result, unsigned int maxlen);
- int (*end_io) (struct path_selector *ps, struct dm_path *path);
+ int (*start_io) (struct path_selector *ps, struct dm_path *path,
+ size_t nr_bytes);
+ int (*end_io) (struct path_selector *ps, struct dm_path *path,
+ size_t nr_bytes);
};
/* Register a path selector */
Index: 2.6.29-rc8/drivers/md/dm-round-robin.c
===================================================================
--- 2.6.29-rc8.orig/drivers/md/dm-round-robin.c
+++ 2.6.29-rc8/drivers/md/dm-round-robin.c
@@ -161,7 +161,7 @@ static int rr_reinstate_path(struct path
}
static struct dm_path *rr_select_path(struct path_selector *ps,
- unsigned *repeat_count)
+ unsigned *repeat_count, size_t nr_bytes)
{
struct selector *s = (struct selector *) ps->context;
struct path_info *pi = NULL;
^ permalink raw reply [flat|nested] 4+ messages in thread* [PATCH 2/3] dm-mpath: add queue-length oriented dynamic load balancer
2009-03-18 8:34 Subject: [PATCH 0/3] dm-mpath: dynamic load balancers (v1) Kiyoshi Ueda
2009-03-18 8:38 ` [PATCH 1/3] dm-mpath: interface change for dynamic load balancers Kiyoshi Ueda
@ 2009-03-18 8:39 ` Kiyoshi Ueda
2009-03-18 8:40 ` [PATCH 3/3] dm-mpath: add service-time " Kiyoshi Ueda
2 siblings, 0 replies; 4+ messages in thread
From: Kiyoshi Ueda @ 2009-03-18 8:39 UTC (permalink / raw)
To: Alasdair Kergon; +Cc: device-mapper development, stefan.bader
This patch adds a dynamic load balancer, dm-queue-length, which
balances the number of in-flight I/Os.
The code is based on the patch posted by Stefan Bader:
https://www.redhat.com/archives/dm-devel/2005-October/msg00050.html
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Cc: Vijayakumar Balasubramanian <vijayakumar@hp.com>
Cc: Alasdair G Kergon <agk@redhat.com>
---
drivers/md/Kconfig | 9 +
drivers/md/Makefile | 1
drivers/md/dm-queue-length.c | 257 +++++++++++++++++++++++++++++++++++++++++++
3 files changed, 267 insertions(+)
Index: 2.6.29-rc8/drivers/md/dm-queue-length.c
===================================================================
--- /dev/null
+++ 2.6.29-rc8/drivers/md/dm-queue-length.c
@@ -0,0 +1,257 @@
+/*
+ * Copyright (C) 2004-2005 IBM Corp. All Rights Reserved.
+ * Copyright (C) 2006-2009 NEC Corporation.
+ *
+ * dm-queue-length.c
+ *
+ * Module Author: Stefan Bader, IBM
+ * Modified by: Kiyoshi Ueda, NEC
+ *
+ * This file is released under the GPL.
+ *
+ * queue-length path selector, which chooses a path with the least number of
+ * in-flight I/Os.
+ */
+
+#include "dm.h"
+#include "dm-path-selector.h"
+
+#include <linux/slab.h>
+#include <linux/ctype.h>
+#include <linux/errno.h>
+#include <linux/module.h>
+#include <asm/atomic.h>
+
+#define DM_MSG_PREFIX "multipath queue-length"
+#define QL_MIN_IO 128
+#define QL_VERSION "0.1.0"
+
+struct selector {
+ struct list_head valid_paths;
+ struct list_head failed_paths;
+};
+
+struct path_info {
+ struct list_head list;
+ struct dm_path *path;
+ unsigned int repeat_count;
+ atomic_t qlen;
+};
+
+static struct selector *alloc_selector(void)
+{
+ struct selector *s = kmalloc(sizeof(*s), GFP_KERNEL);
+
+ if (s) {
+ INIT_LIST_HEAD(&s->valid_paths);
+ INIT_LIST_HEAD(&s->failed_paths);
+ }
+
+ return s;
+}
+
+static int ql_create(struct path_selector *ps, unsigned argc, char **argv)
+{
+ struct selector *s = alloc_selector();
+
+ if (!s)
+ return -ENOMEM;
+
+ ps->context = s;
+ return 0;
+}
+
+static void ql_free_paths(struct list_head *paths)
+{
+ struct path_info *pi, *next;
+
+ list_for_each_entry_safe(pi, next, paths, list) {
+ list_del(&pi->list);
+ kfree(pi);
+ }
+}
+
+static void ql_destroy(struct path_selector *ps)
+{
+ struct selector *s = (struct selector *) ps->context;
+
+ ql_free_paths(&s->valid_paths);
+ ql_free_paths(&s->failed_paths);
+ kfree(s);
+ ps->context = NULL;
+}
+
+static int ql_status(struct path_selector *ps, struct dm_path *path,
+ status_type_t type, char *result, unsigned int maxlen)
+{
+ int sz = 0;
+ struct path_info *pi;
+
+ /* When called with (path == NULL), return selector status/args. */
+ if (!path)
+ DMEMIT("0 ");
+ else {
+ pi = path->pscontext;
+
+ switch (type) {
+ case STATUSTYPE_INFO:
+ DMEMIT("%u ", atomic_read(&pi->qlen));
+ break;
+ case STATUSTYPE_TABLE:
+ DMEMIT("%u ", pi->repeat_count);
+ break;
+ }
+ }
+
+ return sz;
+}
+
+static int ql_add_path(struct path_selector *ps, struct dm_path *path,
+ int argc, char **argv, char **error)
+{
+ struct selector *s = (struct selector *) ps->context;
+ struct path_info *pi;
+ unsigned int repeat_count = QL_MIN_IO;
+
+ /* Parse the arguments */
+ if (argc > 1) {
+ *error = "queue-length ps: incorrect number of arguments";
+ return -EINVAL;
+ }
+
+ /* First path argument is number of I/Os before switching path. */
+ if ((argc == 1) && (sscanf(argv[0], "%u", &repeat_count) != 1)) {
+ *error = "queue-length ps: invalid repeat count";
+ return -EINVAL;
+ }
+
+ /* Allocate the path information structure */
+ pi = kmalloc(sizeof(*pi), GFP_KERNEL);
+ if (!pi) {
+ *error = "queue-length ps: Error allocating path information";
+ return -ENOMEM;
+ }
+
+ pi->path = path;
+ pi->repeat_count = repeat_count;
+ atomic_set(&pi->qlen, 0);
+
+ path->pscontext = pi;
+
+ list_add_tail(&pi->list, &s->valid_paths);
+
+ return 0;
+}
+
+static void ql_fail_path(struct path_selector *ps, struct dm_path *path)
+{
+ struct selector *s = (struct selector *) ps->context;
+ struct path_info *pi = path->pscontext;
+
+ list_move(&pi->list, &s->failed_paths);
+}
+
+static int ql_reinstate_path(struct path_selector *ps, struct dm_path *path)
+{
+ struct selector *s = (struct selector *) ps->context;
+ struct path_info *pi = path->pscontext;
+
+ list_move_tail(&pi->list, &s->valid_paths);
+
+ return 0;
+}
+
+static struct dm_path *ql_select_path(struct path_selector *ps,
+ unsigned *repeat_count, size_t nr_bytes)
+{
+ struct selector *s = (struct selector *) ps->context;
+ struct path_info *pi = NULL, *best = NULL;
+
+ if (list_empty(&s->valid_paths))
+ return NULL;
+
+ /* Change preferred (first in list) path to evenly balance. */
+ list_move_tail(s->valid_paths.next, &s->valid_paths);
+
+ list_for_each_entry(pi, &s->valid_paths, list) {
+ if (!best ||
+ (atomic_read(&pi->qlen) < atomic_read(&best->qlen)))
+ best = pi;
+
+ if (!atomic_read(&best->qlen))
+ break;
+ }
+
+ if (!best)
+ return NULL;
+
+ *repeat_count = best->repeat_count;
+
+ return best->path;
+}
+
+static int ql_start_io(struct path_selector *ps, struct dm_path *path,
+ size_t nr_bytes)
+{
+ struct path_info *pi = path->pscontext;
+
+ atomic_inc(&pi->qlen);
+
+ return 0;
+}
+
+static int ql_end_io(struct path_selector *ps, struct dm_path *path,
+ size_t nr_bytes)
+{
+ struct path_info *pi = path->pscontext;
+
+ atomic_dec(&pi->qlen);
+
+ return 0;
+}
+
+static struct path_selector_type ql_ps = {
+ .name = "queue-length",
+ .module = THIS_MODULE,
+ .table_args = 1,
+ .info_args = 1,
+ .create = ql_create,
+ .destroy = ql_destroy,
+ .status = ql_status,
+ .add_path = ql_add_path,
+ .fail_path = ql_fail_path,
+ .reinstate_path = ql_reinstate_path,
+ .select_path = ql_select_path,
+ .start_io = ql_start_io,
+ .end_io = ql_end_io,
+};
+
+static int __init dm_ql_init(void)
+{
+ int r = dm_register_path_selector(&ql_ps);
+
+ if (r < 0)
+ DMERR("register failed %d", r);
+
+ DMINFO("version " QL_VERSION " loaded");
+
+ return r;
+}
+
+static void __exit dm_ql_exit(void)
+{
+ int r = dm_unregister_path_selector(&ql_ps);
+
+ if (r < 0)
+ DMERR("unregister failed %d", r);
+}
+
+module_init(dm_ql_init);
+module_exit(dm_ql_exit);
+
+MODULE_AUTHOR("Stefan Bader <Stefan.Bader at de.ibm.com>");
+MODULE_DESCRIPTION(
+ "(C) Copyright IBM Corp. 2004,2005 All Rights Reserved.\n"
+ DM_NAME " path selector to balance the number of in-flight I/Os"
+);
+MODULE_LICENSE("GPL");
Index: 2.6.29-rc8/drivers/md/Makefile
===================================================================
--- 2.6.29-rc8.orig/drivers/md/Makefile
+++ 2.6.29-rc8/drivers/md/Makefile
@@ -34,6 +34,7 @@ obj-$(CONFIG_BLK_DEV_DM) += dm-mod.o
obj-$(CONFIG_DM_CRYPT) += dm-crypt.o
obj-$(CONFIG_DM_DELAY) += dm-delay.o
obj-$(CONFIG_DM_MULTIPATH) += dm-multipath.o dm-round-robin.o
+obj-$(CONFIG_DM_MULTIPATH_QL) += dm-queue-length.o
obj-$(CONFIG_DM_SNAPSHOT) += dm-snapshot.o
obj-$(CONFIG_DM_MIRROR) += dm-mirror.o dm-log.o dm-region-hash.o
obj-$(CONFIG_DM_ZERO) += dm-zero.o
Index: 2.6.29-rc8/drivers/md/Kconfig
===================================================================
--- 2.6.29-rc8.orig/drivers/md/Kconfig
+++ 2.6.29-rc8/drivers/md/Kconfig
@@ -274,6 +274,15 @@ config DM_MULTIPATH
---help---
Allow volume managers to support multipath hardware.
+config DM_MULTIPATH_QL
+ tristate "I/O Path Selector based on the number of in-flight I/Os"
+ depends on DM_MULTIPATH
+ ---help---
+ This path selector is a dynamic load balancer which selects
+ a path having the least number of in-flight I/Os.
+
+ If unsure, say N.
+
config DM_DELAY
tristate "I/O delaying target (EXPERIMENTAL)"
depends on BLK_DEV_DM && EXPERIMENTAL
^ permalink raw reply [flat|nested] 4+ messages in thread* [PATCH 3/3] dm-mpath: add service-time oriented dynamic load balancer
2009-03-18 8:34 Subject: [PATCH 0/3] dm-mpath: dynamic load balancers (v1) Kiyoshi Ueda
2009-03-18 8:38 ` [PATCH 1/3] dm-mpath: interface change for dynamic load balancers Kiyoshi Ueda
2009-03-18 8:39 ` [PATCH 2/3] dm-mpath: add queue-length oriented dynamic load balancer Kiyoshi Ueda
@ 2009-03-18 8:40 ` Kiyoshi Ueda
2 siblings, 0 replies; 4+ messages in thread
From: Kiyoshi Ueda @ 2009-03-18 8:40 UTC (permalink / raw)
To: Alasdair Kergon; +Cc: device-mapper development
This patch adds a service time oriented dynamic load balancer,
dm-service-time, which selects a path with the shortest estimated
service time for the incoming I/O.
The service time is estimated by dividing the in-flight I/O size
with performance value of each path.
The performance value can be given as a table argument at the table
loading time. If no performance value is given, all paths are
recognized as equal performance.
Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
---
drivers/md/Kconfig | 9 +
drivers/md/Makefile | 1
drivers/md/dm-service-time.c | 301 +++++++++++++++++++++++++++++++++++++++++++
3 files changed, 311 insertions(+)
Index: 2.6.29-rc8/drivers/md/dm-service-time.c
===================================================================
--- /dev/null
+++ 2.6.29-rc8/drivers/md/dm-service-time.c
@@ -0,0 +1,301 @@
+/*
+ * Copyright (C) 2007-2009 NEC Corporation. All Rights Reserved.
+ *
+ * Module Author: Kiyoshi Ueda
+ *
+ * This file is released under the GPL.
+ *
+ * Throughput oriented path selector.
+ */
+
+#include "dm.h"
+#include "dm-path-selector.h"
+
+#define DM_MSG_PREFIX "multipath service-time"
+#define ST_MIN_IO 1
+#define ST_VERSION "0.1.0"
+
+struct selector {
+ struct list_head valid_paths;
+ struct list_head failed_paths;
+};
+
+struct path_info {
+ struct list_head list;
+ struct dm_path *path;
+ unsigned int repeat_count;
+ size_t perf;
+ atomic_t in_flight_size; /* Total size of in-flight I/Os */
+};
+
+static struct selector *alloc_selector(void)
+{
+ struct selector *s = kmalloc(sizeof(*s), GFP_KERNEL);
+
+ if (s) {
+ INIT_LIST_HEAD(&s->valid_paths);
+ INIT_LIST_HEAD(&s->failed_paths);
+ }
+
+ return s;
+}
+
+static int st_create(struct path_selector *ps, unsigned argc, char **argv)
+{
+ struct selector *s = alloc_selector();
+
+ if (!s)
+ return -ENOMEM;
+
+ ps->context = s;
+ return 0;
+}
+
+static void free_paths(struct list_head *paths)
+{
+ struct path_info *pi, *next;
+
+ list_for_each_entry_safe(pi, next, paths, list) {
+ list_del(&pi->list);
+ kfree(pi);
+ }
+}
+
+static void st_destroy(struct path_selector *ps)
+{
+ struct selector *s = (struct selector *) ps->context;
+
+ free_paths(&s->valid_paths);
+ free_paths(&s->failed_paths);
+ kfree(s);
+ ps->context = NULL;
+}
+
+static int st_status(struct path_selector *ps, struct dm_path *path,
+ status_type_t type, char *result, unsigned int maxlen)
+{
+ int sz = 0;
+ struct path_info *pi;
+
+ if (!path)
+ DMEMIT("0 ");
+ else {
+ pi = path->pscontext;
+
+ switch (type) {
+ case STATUSTYPE_INFO:
+ DMEMIT("%u %lu ", atomic_read(&pi->in_flight_size),
+ pi->perf);
+ break;
+ case STATUSTYPE_TABLE:
+ DMEMIT("%u %lu ", pi->repeat_count, pi->perf);
+ break;
+ }
+ }
+
+ return sz;
+}
+
+static int st_add_path(struct path_selector *ps, struct dm_path *path,
+ int argc, char **argv, char **error)
+{
+ struct selector *s = (struct selector *) ps->context;
+ struct path_info *pi;
+ unsigned int repeat_count = ST_MIN_IO;
+ size_t perf = 1;
+
+ if (argc > 2) {
+ *error = "service-time ps: incorrect number of arguments";
+ return -EINVAL;
+ }
+
+ /* First path argument is number of I/Os before switching path. */
+ if ((argc > 0) && (sscanf(argv[0], "%u", &repeat_count) != 1)) {
+ *error = "service-time ps: invalid repeat count";
+ return -EINVAL;
+ }
+
+ /*
+ * Second path argument is a relative performance value.
+ * If 0 is given, the path isn't used while other paths having
+ * a positive value are available.
+ */
+ if ((argc == 2) && (sscanf(argv[1], "%lu", &perf) != 1)) {
+ *error = "service-time ps: invalid performance value";
+ return -EINVAL;
+ }
+
+ /* allocate the path */
+ pi = kmalloc(sizeof(*pi), GFP_KERNEL);
+ if (!pi) {
+ *error = "service-time ps: Error allocating path context";
+ return -ENOMEM;
+ }
+
+ pi->path = path;
+ pi->repeat_count = repeat_count;
+ pi->perf = perf;
+ atomic_set(&pi->in_flight_size, 0);
+
+ path->pscontext = pi;
+
+ list_add_tail(&pi->list, &s->valid_paths);
+
+ return 0;
+}
+
+static void st_fail_path(struct path_selector *ps, struct dm_path *path)
+{
+ struct selector *s = (struct selector *) ps->context;
+ struct path_info *pi = path->pscontext;
+
+ list_move(&pi->list, &s->failed_paths);
+}
+
+static int st_reinstate_path(struct path_selector *ps, struct dm_path *path)
+{
+ struct selector *s = (struct selector *) ps->context;
+ struct path_info *pi = path->pscontext;
+
+ list_move_tail(&pi->list, &s->valid_paths);
+
+ return 0;
+}
+
+/*
+ * Returns:
+ * < 0 : pi1 is better
+ * 0 : no difference between pi1 and pi2
+ * > 0 : pi2 is better
+ */
+static int st_compare_load(struct path_info *pi1, struct path_info *pi2,
+ size_t incoming)
+{
+ size_t sz1, sz2;
+
+ sz1 = atomic_read(&pi1->in_flight_size);
+ sz2 = atomic_read(&pi2->in_flight_size);
+
+ /*
+ * Case 1: Both have same performace value. Choose less loaded path.
+ */
+ if (pi1->perf == pi2->perf)
+ return sz1 - sz2;
+
+ /*
+ * Case 2a: Both have same load. Choose higher performance path.
+ * Case 2b: One path has no performance value. Choose the other one.
+ */
+ if (sz1 == sz2 || !pi1->perf || !pi2->perf)
+ return pi2->perf - pi1->perf;
+
+ /*
+ * Case 3: Calculate service time. Choose faster path.
+ * if ((sz1+incoming)/pi1->perf < (sz2+incoming)/pi2->perf) pi1
+ * if ((sz1+incoming)/pi1->perf > (sz2+incoming)/pi2->perf) pi2
+ */
+ sz1 += incoming;
+ sz2 += incoming;
+ while (sz1 && sz2 && (sz1 < pi1->perf) && (sz2 < pi2->perf)) {
+ /* Size is not big enough to compare by division. Shift up */
+ sz1 <<= 2;
+ sz2 <<= 2;
+ }
+ do_div(sz1, pi1->perf);
+ do_div(sz2, pi2->perf);
+
+ if (sz1 != sz2)
+ return sz1 - sz2;
+
+ /*
+ * Case 4: Service time is equal. Choose higher performance path.
+ */
+ return pi2->perf - pi1->perf;
+}
+
+static struct dm_path *st_select_path(struct path_selector *ps,
+ unsigned *repeat_count, size_t nr_bytes)
+{
+ struct selector *s = (struct selector *) ps->context;
+ struct path_info *pi = NULL, *best = NULL;
+
+ if (list_empty(&s->valid_paths))
+ return NULL;
+
+ /* Change preferred (first in list) path to evenly balance. */
+ list_move_tail(s->valid_paths.next, &s->valid_paths);
+
+ list_for_each_entry(pi, &s->valid_paths, list)
+ if (!best || (st_compare_load(pi, best, nr_bytes) < 0))
+ best = pi;
+
+ if (!best)
+ return NULL;
+
+ *repeat_count = best->repeat_count;
+
+ return best->path;
+}
+
+static int st_start_io(struct path_selector *ps, struct dm_path *path,
+ size_t nr_bytes)
+{
+ struct path_info *pi = path->pscontext;
+
+ atomic_add(nr_bytes, &pi->in_flight_size);
+
+ return 0;
+}
+
+static int st_end_io(struct path_selector *ps, struct dm_path *path,
+ size_t nr_bytes)
+{
+ struct path_info *pi = path->pscontext;
+
+ atomic_sub(nr_bytes, &pi->in_flight_size);
+
+ return 0;
+}
+
+static struct path_selector_type st_ps = {
+ .name = "service-time",
+ .module = THIS_MODULE,
+ .table_args = 2,
+ .info_args = 2,
+ .create = st_create,
+ .destroy = st_destroy,
+ .status = st_status,
+ .add_path = st_add_path,
+ .fail_path = st_fail_path,
+ .reinstate_path = st_reinstate_path,
+ .select_path = st_select_path,
+ .start_io = st_start_io,
+ .end_io = st_end_io,
+};
+
+static int __init dm_st_init(void)
+{
+ int r = dm_register_path_selector(&st_ps);
+
+ if (r < 0)
+ DMERR("register failed %d", r);
+
+ DMINFO("version " ST_VERSION " loaded");
+
+ return r;
+}
+
+static void __exit dm_st_exit(void)
+{
+ int r = dm_unregister_path_selector(&st_ps);
+
+ if (r < 0)
+ DMERR("unregister failed %d", r);
+}
+
+module_init(dm_st_init);
+module_exit(dm_st_exit);
+
+MODULE_DESCRIPTION(DM_NAME " throughput oriented path selector");
+MODULE_AUTHOR("Kiyoshi Ueda <k-ueda@ct.jp.nec.com>");
+MODULE_LICENSE("GPL");
Index: 2.6.29-rc8/drivers/md/Makefile
===================================================================
--- 2.6.29-rc8.orig/drivers/md/Makefile
+++ 2.6.29-rc8/drivers/md/Makefile
@@ -35,6 +35,7 @@ obj-$(CONFIG_DM_CRYPT) += dm-crypt.o
obj-$(CONFIG_DM_DELAY) += dm-delay.o
obj-$(CONFIG_DM_MULTIPATH) += dm-multipath.o dm-round-robin.o
obj-$(CONFIG_DM_MULTIPATH_QL) += dm-queue-length.o
+obj-$(CONFIG_DM_MULTIPATH_ST) += dm-service-time.o
obj-$(CONFIG_DM_SNAPSHOT) += dm-snapshot.o
obj-$(CONFIG_DM_MIRROR) += dm-mirror.o dm-log.o dm-region-hash.o
obj-$(CONFIG_DM_ZERO) += dm-zero.o
Index: 2.6.29-rc8/drivers/md/Kconfig
===================================================================
--- 2.6.29-rc8.orig/drivers/md/Kconfig
+++ 2.6.29-rc8/drivers/md/Kconfig
@@ -283,6 +283,15 @@ config DM_MULTIPATH_QL
If unsure, say N.
+config DM_MULTIPATH_ST
+ tristate "I/O Path Selector based on the service time"
+ depends on DM_MULTIPATH
+ ---help---
+ This path selector is a dynamic load balancer which selects
+ a path to complete the incoming I/O with the shortest time.
+
+ If unsure, say N.
+
config DM_DELAY
tristate "I/O delaying target (EXPERIMENTAL)"
depends on BLK_DEV_DM && EXPERIMENTAL
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