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authorKiyoshi Ueda <k-ueda@ct.jp.nec.com>2009-06-22 10:12:28 +0100
committerAlasdair G Kergon <agk@redhat.com>2009-06-22 10:12:28 +0100
commitf392ba889b019602976082bfe7bf486c2594f85c (patch)
tree962e8f354dfe3df2021476412be8d1bcec8a03d0 /drivers/md/dm-service-time.c
parentfd5e033908b7b743b5650790f196761dd930f988 (diff)
downloadlinux-f392ba889b019602976082bfe7bf486c2594f85c.tar.gz
dm mpath: add service time load balancer
This patch adds a service time oriented dynamic load balancer, dm-service-time, which selects the 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 by a 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 considered equal. Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com> Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com> Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Diffstat (limited to 'drivers/md/dm-service-time.c')
-rw-r--r--drivers/md/dm-service-time.c339
1 files changed, 339 insertions, 0 deletions
diff --git a/drivers/md/dm-service-time.c b/drivers/md/dm-service-time.c
new file mode 100644
index 00000000000..cfa668f46c4
--- /dev/null
+++ b/drivers/md/dm-service-time.c
@@ -0,0 +1,339 @@
+/*
+ * 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_MAX_RELATIVE_THROUGHPUT 100
+#define ST_MAX_RELATIVE_THROUGHPUT_SHIFT 7
+#define ST_MAX_INFLIGHT_SIZE ((size_t)-1 >> ST_MAX_RELATIVE_THROUGHPUT_SHIFT)
+#define ST_VERSION "0.2.0"
+
+struct selector {
+ struct list_head valid_paths;
+ struct list_head failed_paths;
+};
+
+struct path_info {
+ struct list_head list;
+ struct dm_path *path;
+ unsigned repeat_count;
+ unsigned relative_throughput;
+ 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 = 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 maxlen)
+{
+ unsigned sz = 0;
+ struct path_info *pi;
+
+ if (!path)
+ DMEMIT("0 ");
+ else {
+ pi = path->pscontext;
+
+ switch (type) {
+ case STATUSTYPE_INFO:
+ DMEMIT("%d %u ", atomic_read(&pi->in_flight_size),
+ pi->relative_throughput);
+ break;
+ case STATUSTYPE_TABLE:
+ DMEMIT("%u %u ", pi->repeat_count,
+ pi->relative_throughput);
+ 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 = ps->context;
+ struct path_info *pi;
+ unsigned repeat_count = ST_MIN_IO;
+ unsigned relative_throughput = 1;
+
+ /*
+ * Arguments: [<repeat_count> [<relative_throughput>]]
+ * <repeat_count>: The number of I/Os before switching path.
+ * If not given, default (ST_MIN_IO) is used.
+ * <relative_throughput>: The relative throughput value of
+ * the path among all paths in the path-group.
+ * The valid range: 0-<ST_MAX_RELATIVE_THROUGHPUT>
+ * If not given, minimum value '1' is used.
+ * If '0' is given, the path isn't selected while
+ * other paths having a positive value are
+ * available.
+ */
+ if (argc > 2) {
+ *error = "service-time ps: incorrect number of arguments";
+ return -EINVAL;
+ }
+
+ if (argc && (sscanf(argv[0], "%u", &repeat_count) != 1)) {
+ *error = "service-time ps: invalid repeat count";
+ return -EINVAL;
+ }
+
+ if ((argc == 2) &&
+ (sscanf(argv[1], "%u", &relative_throughput) != 1 ||
+ relative_throughput > ST_MAX_RELATIVE_THROUGHPUT)) {
+ *error = "service-time ps: invalid relative_throughput 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->relative_throughput = relative_throughput;
+ 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 = 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 = ps->context;
+ struct path_info *pi = path->pscontext;
+
+ list_move_tail(&pi->list, &s->valid_paths);
+
+ return 0;
+}
+
+/*
+ * Compare the estimated service time of 2 paths, pi1 and pi2,
+ * for the incoming I/O.
+ *
+ * Returns:
+ * < 0 : pi1 is better
+ * 0 : no difference between pi1 and pi2
+ * > 0 : pi2 is better
+ *
+ * Description:
+ * Basically, the service time is estimated by:
+ * ('pi->in-flight-size' + 'incoming') / 'pi->relative_throughput'
+ * To reduce the calculation, some optimizations are made.
+ * (See comments inline)
+ */
+static int st_compare_load(struct path_info *pi1, struct path_info *pi2,
+ size_t incoming)
+{
+ size_t sz1, sz2, st1, st2;
+
+ sz1 = atomic_read(&pi1->in_flight_size);
+ sz2 = atomic_read(&pi2->in_flight_size);
+
+ /*
+ * Case 1: Both have same throughput value. Choose less loaded path.
+ */
+ if (pi1->relative_throughput == pi2->relative_throughput)
+ return sz1 - sz2;
+
+ /*
+ * Case 2a: Both have same load. Choose higher throughput path.
+ * Case 2b: One path has no throughput value. Choose the other one.
+ */
+ if (sz1 == sz2 ||
+ !pi1->relative_throughput || !pi2->relative_throughput)
+ return pi2->relative_throughput - pi1->relative_throughput;
+
+ /*
+ * Case 3: Calculate service time. Choose faster path.
+ * Service time using pi1:
+ * st1 = (sz1 + incoming) / pi1->relative_throughput
+ * Service time using pi2:
+ * st2 = (sz2 + incoming) / pi2->relative_throughput
+ *
+ * To avoid the division, transform the expression to use
+ * multiplication.
+ * Because ->relative_throughput > 0 here, if st1 < st2,
+ * the expressions below are the same meaning:
+ * (sz1 + incoming) / pi1->relative_throughput <
+ * (sz2 + incoming) / pi2->relative_throughput
+ * (sz1 + incoming) * pi2->relative_throughput <
+ * (sz2 + incoming) * pi1->relative_throughput
+ * So use the later one.
+ */
+ sz1 += incoming;
+ sz2 += incoming;
+ if (unlikely(sz1 >= ST_MAX_INFLIGHT_SIZE ||
+ sz2 >= ST_MAX_INFLIGHT_SIZE)) {
+ /*
+ * Size may be too big for multiplying pi->relative_throughput
+ * and overflow.
+ * To avoid the overflow and mis-selection, shift down both.
+ */
+ sz1 >>= ST_MAX_RELATIVE_THROUGHPUT_SHIFT;
+ sz2 >>= ST_MAX_RELATIVE_THROUGHPUT_SHIFT;
+ }
+ st1 = sz1 * pi2->relative_throughput;
+ st2 = sz2 * pi1->relative_throughput;
+ if (st1 != st2)
+ return st1 - st2;
+
+ /*
+ * Case 4: Service time is equal. Choose higher throughput path.
+ */
+ return pi2->relative_throughput - pi1->relative_throughput;
+}
+
+static struct dm_path *st_select_path(struct path_selector *ps,
+ unsigned *repeat_count, size_t nr_bytes)
+{
+ struct selector *s = 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");