From: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
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>
---
drivers/md/Kconfig | 9 +
drivers/md/Makefile | 1
drivers/md/dm-queue-length.c | 257 +++++++++++++++++++++++++++++++++++++++++++
3 files changed, 267 insertions(+)
Index: linux-2.6.30-rc4/drivers/md/Kconfig
===================================================================
--- linux-2.6.30-rc4.orig/drivers/md/Kconfig
+++ linux-2.6.30-rc4/drivers/md/Kconfig
@@ -259,6 +259,15 @@ 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
Index: linux-2.6.30-rc4/drivers/md/Makefile
===================================================================
--- linux-2.6.30-rc4.orig/drivers/md/Makefile
+++ linux-2.6.30-rc4/drivers/md/Makefile
@@ -40,6 +40,7 @@ obj-$(CONFIG_DM_CRYPT) += dm-crypt.o
obj-$(CONFIG_DM_DELAY) += dm-delay.o
obj-$(CONFIG_DM_IOBAND) += dm-ioband.o
obj-$(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_LOG_CLUSTERED) += dm-log-clustered.o
Index: linux-2.6.30-rc4/drivers/md/dm-queue-length.c
===================================================================
--- /dev/null
+++ linux-2.6.30-rc4/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.
+ *
+ * Load balancing path selector to choose 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 = kzalloc(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 *cpi, *npi;
+
+ list_for_each_entry_safe(cpi, npi, paths, list) {
+ list_del(&cpi->list);
+ cpi->path->pscontext = NULL;
+ kfree(cpi);
+ }
+}
+
+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_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)
+{
+ 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)
+{
+ 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)
+{
+ struct path_info *pi = path->pscontext;
+
+ atomic_dec(&pi->qlen);
+
+ return 0;
+}
+
+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 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 " load balancing path selector (dm-queue-length.c version "
+ QL_VERSION ")"
+);
+MODULE_LICENSE("GPL");