Skip to content
Fetching contributors…
Cannot retrieve contributors at this time
284 lines (228 sloc) 5.91 KB
/*
* 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 - 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 <linux/atomic.h>
#define DM_MSG_PREFIX "multipath queue-length"
#define QL_MIN_IO 1
#define QL_VERSION "0.2.0"
struct selector {
struct list_head valid_paths;
struct list_head failed_paths;
spinlock_t lock;
};
struct path_info {
struct list_head list;
struct dm_path *path;
unsigned repeat_count;
atomic_t qlen; /* the number 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);
spin_lock_init(&s->lock);
}
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 = 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 maxlen)
{
unsigned sz = 0;
struct path_info *pi;
/* When called with NULL path, return selector status/args. */
if (!path)
DMEMIT("0 ");
else {
pi = path->pscontext;
switch (type) {
case STATUSTYPE_INFO:
DMEMIT("%d ", 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 = ps->context;
struct path_info *pi;
unsigned repeat_count = QL_MIN_IO;
char dummy;
unsigned long flags;
/*
* Arguments: [<repeat_count>]
* <repeat_count>: The number of I/Os before switching path.
* If not given, default (QL_MIN_IO) is used.
*/
if (argc > 1) {
*error = "queue-length ps: incorrect number of arguments";
return -EINVAL;
}
if ((argc == 1) && (sscanf(argv[0], "%u%c", &repeat_count, &dummy) != 1)) {
*error = "queue-length ps: invalid repeat count";
return -EINVAL;
}
if (repeat_count > 1) {
DMWARN_LIMIT("repeat_count > 1 is deprecated, using 1 instead");
repeat_count = 1;
}
/* 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;
spin_lock_irqsave(&s->lock, flags);
list_add_tail(&pi->list, &s->valid_paths);
spin_unlock_irqrestore(&s->lock, flags);
return 0;
}
static void ql_fail_path(struct path_selector *ps, struct dm_path *path)
{
struct selector *s = ps->context;
struct path_info *pi = path->pscontext;
unsigned long flags;
spin_lock_irqsave(&s->lock, flags);
list_move(&pi->list, &s->failed_paths);
spin_unlock_irqrestore(&s->lock, flags);
}
static int ql_reinstate_path(struct path_selector *ps, struct dm_path *path)
{
struct selector *s = ps->context;
struct path_info *pi = path->pscontext;
unsigned long flags;
spin_lock_irqsave(&s->lock, flags);
list_move_tail(&pi->list, &s->valid_paths);
spin_unlock_irqrestore(&s->lock, flags);
return 0;
}
/*
* Select a path having the minimum number of in-flight I/Os
*/
static struct dm_path *ql_select_path(struct path_selector *ps, size_t nr_bytes)
{
struct selector *s = ps->context;
struct path_info *pi = NULL, *best = NULL;
struct dm_path *ret = NULL;
unsigned long flags;
spin_lock_irqsave(&s->lock, flags);
if (list_empty(&s->valid_paths))
goto out;
/* 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)
goto out;
ret = best->path;
out:
spin_unlock_irqrestore(&s->lock, flags);
return ret;
}
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");
Something went wrong with that request. Please try again.