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![Mike Snitzer](/assets/img/avatar_default.png)
Now that dm-mpath core is lockless in the per-IO fast path it is critical, for performance, to have the .select_path hook (rr_select_path) also be as lockless as possible. The new percpu members of 'struct selector' allow for lockless support of 'repeat_count' governed repeat use of a previously selected path. If a path fails while it is 'current_path' the worst case is concurrent IO might be mapped to the failed path until the .fail_path hook (rr_fail_path) is called. Signed-off-by: Mike Snitzer <snitzer@redhat.com>
272 lines
6 KiB
C
272 lines
6 KiB
C
/*
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* Copyright (C) 2003 Sistina Software.
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* Copyright (C) 2004-2005 Red Hat, Inc. All rights reserved.
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*
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* Module Author: Heinz Mauelshagen
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*
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* This file is released under the GPL.
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*
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* Round-robin path selector.
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*/
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#include <linux/device-mapper.h>
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#include "dm-path-selector.h"
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#include <linux/slab.h>
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#include <linux/module.h>
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#define DM_MSG_PREFIX "multipath round-robin"
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#define RR_MIN_IO 1000
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#define RR_VERSION "1.1.0"
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/*-----------------------------------------------------------------
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* Path-handling code, paths are held in lists
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*---------------------------------------------------------------*/
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struct path_info {
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struct list_head list;
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struct dm_path *path;
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unsigned repeat_count;
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};
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static void free_paths(struct list_head *paths)
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{
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struct path_info *pi, *next;
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list_for_each_entry_safe(pi, next, paths, list) {
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list_del(&pi->list);
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kfree(pi);
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}
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}
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/*-----------------------------------------------------------------
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* Round-robin selector
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*---------------------------------------------------------------*/
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struct selector {
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struct list_head valid_paths;
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struct list_head invalid_paths;
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spinlock_t lock;
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struct dm_path * __percpu *current_path;
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struct percpu_counter repeat_count;
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};
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static void set_percpu_current_path(struct selector *s, struct dm_path *path)
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{
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int cpu;
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for_each_possible_cpu(cpu)
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*per_cpu_ptr(s->current_path, cpu) = path;
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}
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static struct selector *alloc_selector(void)
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{
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struct selector *s = kmalloc(sizeof(*s), GFP_KERNEL);
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if (!s)
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return NULL;
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INIT_LIST_HEAD(&s->valid_paths);
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INIT_LIST_HEAD(&s->invalid_paths);
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spin_lock_init(&s->lock);
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s->current_path = alloc_percpu(struct dm_path *);
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if (!s->current_path)
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goto out_current_path;
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set_percpu_current_path(s, NULL);
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if (percpu_counter_init(&s->repeat_count, 0, GFP_KERNEL))
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goto out_repeat_count;
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return s;
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out_repeat_count:
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free_percpu(s->current_path);
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out_current_path:
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kfree(s);
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return NULL;;
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}
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static int rr_create(struct path_selector *ps, unsigned argc, char **argv)
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{
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struct selector *s;
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s = alloc_selector();
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if (!s)
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return -ENOMEM;
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ps->context = s;
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return 0;
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}
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static void rr_destroy(struct path_selector *ps)
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{
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struct selector *s = ps->context;
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free_paths(&s->valid_paths);
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free_paths(&s->invalid_paths);
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free_percpu(s->current_path);
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percpu_counter_destroy(&s->repeat_count);
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kfree(s);
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ps->context = NULL;
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}
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static int rr_status(struct path_selector *ps, struct dm_path *path,
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status_type_t type, char *result, unsigned int maxlen)
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{
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struct path_info *pi;
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int sz = 0;
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if (!path)
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DMEMIT("0 ");
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else {
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switch(type) {
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case STATUSTYPE_INFO:
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break;
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case STATUSTYPE_TABLE:
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pi = path->pscontext;
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DMEMIT("%u ", pi->repeat_count);
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break;
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}
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}
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return sz;
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}
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/*
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* Called during initialisation to register each path with an
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* optional repeat_count.
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*/
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static int rr_add_path(struct path_selector *ps, struct dm_path *path,
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int argc, char **argv, char **error)
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{
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struct selector *s = ps->context;
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struct path_info *pi;
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unsigned repeat_count = RR_MIN_IO;
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char dummy;
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unsigned long flags;
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if (argc > 1) {
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*error = "round-robin ps: incorrect number of arguments";
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return -EINVAL;
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}
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/* First path argument is number of I/Os before switching path */
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if ((argc == 1) && (sscanf(argv[0], "%u%c", &repeat_count, &dummy) != 1)) {
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*error = "round-robin ps: invalid repeat count";
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return -EINVAL;
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}
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/* allocate the path */
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pi = kmalloc(sizeof(*pi), GFP_KERNEL);
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if (!pi) {
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*error = "round-robin ps: Error allocating path context";
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return -ENOMEM;
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}
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pi->path = path;
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pi->repeat_count = repeat_count;
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path->pscontext = pi;
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spin_lock_irqsave(&s->lock, flags);
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list_add_tail(&pi->list, &s->valid_paths);
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spin_unlock_irqrestore(&s->lock, flags);
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return 0;
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}
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static void rr_fail_path(struct path_selector *ps, struct dm_path *p)
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{
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unsigned long flags;
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struct selector *s = ps->context;
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struct path_info *pi = p->pscontext;
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spin_lock_irqsave(&s->lock, flags);
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if (p == *this_cpu_ptr(s->current_path))
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set_percpu_current_path(s, NULL);
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list_move(&pi->list, &s->invalid_paths);
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spin_unlock_irqrestore(&s->lock, flags);
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}
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static int rr_reinstate_path(struct path_selector *ps, struct dm_path *p)
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{
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unsigned long flags;
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struct selector *s = ps->context;
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struct path_info *pi = p->pscontext;
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spin_lock_irqsave(&s->lock, flags);
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list_move(&pi->list, &s->valid_paths);
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spin_unlock_irqrestore(&s->lock, flags);
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return 0;
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}
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static struct dm_path *rr_select_path(struct path_selector *ps, size_t nr_bytes)
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{
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unsigned long flags;
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struct selector *s = ps->context;
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struct path_info *pi = NULL;
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struct dm_path *current_path = NULL;
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current_path = *this_cpu_ptr(s->current_path);
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if (current_path) {
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percpu_counter_dec(&s->repeat_count);
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if (percpu_counter_read_positive(&s->repeat_count) > 0)
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return current_path;
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}
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spin_lock_irqsave(&s->lock, flags);
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if (!list_empty(&s->valid_paths)) {
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pi = list_entry(s->valid_paths.next, struct path_info, list);
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list_move_tail(&pi->list, &s->valid_paths);
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percpu_counter_set(&s->repeat_count, pi->repeat_count);
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set_percpu_current_path(s, pi->path);
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current_path = pi->path;
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}
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spin_unlock_irqrestore(&s->lock, flags);
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return current_path;
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}
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static struct path_selector_type rr_ps = {
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.name = "round-robin",
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.module = THIS_MODULE,
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.table_args = 1,
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.info_args = 0,
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.create = rr_create,
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.destroy = rr_destroy,
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.status = rr_status,
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.add_path = rr_add_path,
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.fail_path = rr_fail_path,
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.reinstate_path = rr_reinstate_path,
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.select_path = rr_select_path,
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};
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static int __init dm_rr_init(void)
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{
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int r = dm_register_path_selector(&rr_ps);
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if (r < 0)
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DMERR("register failed %d", r);
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DMINFO("version " RR_VERSION " loaded");
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return r;
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}
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static void __exit dm_rr_exit(void)
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{
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int r = dm_unregister_path_selector(&rr_ps);
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if (r < 0)
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DMERR("unregister failed %d", r);
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}
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module_init(dm_rr_init);
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module_exit(dm_rr_exit);
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MODULE_DESCRIPTION(DM_NAME " round-robin multipath path selector");
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MODULE_AUTHOR("Sistina Software <dm-devel@redhat.com>");
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MODULE_LICENSE("GPL");
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