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@xxxxxxxxxxxxx>
Signed-off-by: Jun'ichi Nomura <j-nomura@xxxxxxxxxxxxx>
---
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@xxxxxxxxxxxxx>");
+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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