This patch adds a service time oriented dynamic load balancer,
dm-service-time.
Signed-off-by: Kiyoshi Ueda <k-ueda@xxxxxxxxxxxxx>
Signed-off-by: Jun'ichi Nomura <j-nomura@xxxxxxxxxxxxx>
---
drivers/md/Makefile | 2
drivers/md/dm-service-time.c | 312 +++++++++++++++++++++++++++++++++++++++++++
2 files changed, 313 insertions(+), 1 deletion(-)
Index: 2.6.27-rc6/drivers/md/dm-service-time.c
===================================================================
--- /dev/null
+++ 2.6.27-rc6/drivers/md/dm-service-time.c
@@ -0,0 +1,312 @@
+/*
+ * Copyright (C) 2007-2008 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 2
+#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;
+
+ atomic_t in_flight; /* Total size of in-flight I/Os */
+ size_t perf; /* Recent performance of the path */
+ sector_t last_sectors; /* Total sectors of the last disk_stat_read */
+ size_t last_io_ticks; /* io_ticks of the last disk_stat_read */
+};
+
+static struct selector *alloc_selector(void)
+{
+ struct selector *s = kzalloc(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);
+ pi->path->pscontext = NULL;
+ 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("if:%08lu pf:%06lu ",
+ (unsigned long) atomic_read(&pi->in_flight),
+ pi->perf);
+ break;
+ case STATUSTYPE_TABLE:
+ DMEMIT("%u ", pi->repeat_count);
+ 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;
+ struct gendisk *disk = path->dev->bdev->bd_disk;
+
+ if (argc > 1) {
+ *error = "service-time 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 = "service-time ps: invalid repeat count";
+ 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 = 0;
+ pi->last_sectors = disk_stat_read(disk, sectors[READ])
+ + disk_stat_read(disk, sectors[WRITE]);
+ pi->last_io_ticks = disk_stat_read(disk, io_ticks);
+ atomic_set(&pi->in_flight, 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;
+}
+
+static void stats_update(struct path_info *pi)
+{
+ sector_t sectors;
+ size_t io_ticks, tmp;
+ struct gendisk *disk = pi->path->dev->bdev->bd_disk;
+
+ sectors = disk_stat_read(disk, sectors[READ])
+ + disk_stat_read(disk, sectors[WRITE]);
+ io_ticks = disk_stat_read(disk, io_ticks);
+
+ if ((sectors != pi->last_sectors) && (io_ticks != pi->last_io_ticks)) {
+ tmp = (sectors - pi->last_sectors) << 9;
+ do_div(tmp, jiffies_to_msecs((io_ticks - pi->last_io_ticks)));
+ pi->perf = tmp;
+
+ pi->last_sectors = sectors;
+ pi->last_io_ticks = io_ticks;
+ }
+}
+
+static int st_compare_load(struct path_info *pi1, struct path_info *pi2,
+ size_t new_io)
+{
+ size_t if1, if2;
+
+ if1 = atomic_read(&pi1->in_flight);
+ if2 = atomic_read(&pi2->in_flight);
+
+ /*
+ * Case 1: No performace data available. Choose less loaded path.
+ */
+ if (!pi1->perf || !pi2->perf)
+ return if1 - if2;
+
+ /*
+ * Case 2: Calculate service time. Choose faster path.
+ * if ((if1+new_io)/pi1->perf < (if2+new_io)/pi2->perf) pi1.
+ * if ((if1+new_io)/pi1->perf > (if2+new_io)/pi2->perf) pi2.
+ * To avoid do_div(), use
+ * if ((if1+new_io)*pi2->perf < (if2+new_io)*pi1->perf) pi1.
+ * if ((if1+new_io)*pi2->perf > (if2+new_io)*pi1->perf) pi2.
+ */
+ if1 = (if1 + new_io) << 10;
+ if2 = (if2 + new_io) << 10;
+ do_div(if1, pi1->perf);
+ do_div(if2, pi2->perf);
+
+ if (if1 != if2)
+ return if1 - if2;
+
+ /*
+ * Case 3: Service time is equal. Choose faster 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);
+
+ /* Update performance information before best path selection */
+ list_for_each_entry(pi, &s->valid_paths, list)
+ stats_update(pi);
+
+ list_for_each_entry(pi, &s->valid_paths, list) {
+ if (!best)
+ best = pi;
+ else if (st_compare_load(pi, best, nr_bytes) < 0)
+ best = pi;
+ }
+
+ if (best) {
+ *repeat_count = best->repeat_count;
+ return best->path;
+ }
+
+ return NULL;
+}
+
+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);
+
+ 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);
+
+ return 0;
+}
+
+static struct path_selector_type st_ps = {
+ .name = "service-time",
+ .module = THIS_MODULE,
+ .table_args = 1,
+ .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: 2.6.27-rc6/drivers/md/Makefile
===================================================================
--- 2.6.27-rc6.orig/drivers/md/Makefile
+++ 2.6.27-rc6/drivers/md/Makefile
@@ -33,7 +33,7 @@ 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 \
- dm-queue-length.o
+ dm-queue-length.o dm-service-time.o
obj-$(CONFIG_DM_SNAPSHOT) += dm-snapshot.o
obj-$(CONFIG_DM_MIRROR) += dm-mirror.o dm-log.o
obj-$(CONFIG_DM_ZERO) += dm-zero.o
--
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