344 lines
8.2 KiB
C
344 lines
8.2 KiB
C
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/*
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* Copyright (C) 2007-2009 NEC Corporation. All Rights Reserved.
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*
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* Module Author: Kiyoshi Ueda
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*
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* This file is released under the GPL.
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*
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* Throughput oriented path selector.
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*/
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#include "dm.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 service-time"
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#define ST_MIN_IO 1
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#define ST_MAX_RELATIVE_THROUGHPUT 100
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#define ST_MAX_RELATIVE_THROUGHPUT_SHIFT 7
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#define ST_MAX_INFLIGHT_SIZE ((size_t)-1 >> ST_MAX_RELATIVE_THROUGHPUT_SHIFT)
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#define ST_VERSION "0.2.0"
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struct selector {
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struct list_head valid_paths;
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struct list_head failed_paths;
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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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unsigned relative_throughput;
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atomic_t in_flight_size; /* Total size of in-flight I/Os */
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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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INIT_LIST_HEAD(&s->valid_paths);
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INIT_LIST_HEAD(&s->failed_paths);
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}
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return s;
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}
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static int st_create(struct path_selector *ps, unsigned argc, char **argv)
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{
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struct selector *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 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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static void st_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->failed_paths);
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kfree(s);
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ps->context = NULL;
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}
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static int st_status(struct path_selector *ps, struct dm_path *path,
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status_type_t type, char *result, unsigned maxlen)
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{
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unsigned sz = 0;
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struct path_info *pi;
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if (!path)
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DMEMIT("0 ");
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else {
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pi = path->pscontext;
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switch (type) {
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case STATUSTYPE_INFO:
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DMEMIT("%d %u ", atomic_read(&pi->in_flight_size),
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pi->relative_throughput);
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break;
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case STATUSTYPE_TABLE:
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DMEMIT("%u %u ", pi->repeat_count,
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pi->relative_throughput);
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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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static int st_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 = ST_MIN_IO;
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unsigned relative_throughput = 1;
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char dummy;
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/*
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* Arguments: [<repeat_count> [<relative_throughput>]]
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* <repeat_count>: The number of I/Os before switching path.
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* If not given, default (ST_MIN_IO) is used.
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* <relative_throughput>: The relative throughput value of
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* the path among all paths in the path-group.
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* The valid range: 0-<ST_MAX_RELATIVE_THROUGHPUT>
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* If not given, minimum value '1' is used.
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* If '0' is given, the path isn't selected while
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* other paths having a positive value are
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* available.
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*/
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if (argc > 2) {
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*error = "service-time ps: incorrect number of arguments";
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return -EINVAL;
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}
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if (argc && (sscanf(argv[0], "%u%c", &repeat_count, &dummy) != 1)) {
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*error = "service-time ps: invalid repeat count";
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return -EINVAL;
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}
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if ((argc == 2) &&
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(sscanf(argv[1], "%u%c", &relative_throughput, &dummy) != 1 ||
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relative_throughput > ST_MAX_RELATIVE_THROUGHPUT)) {
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*error = "service-time ps: invalid relative_throughput value";
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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 = "service-time 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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pi->relative_throughput = relative_throughput;
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atomic_set(&pi->in_flight_size, 0);
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path->pscontext = pi;
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list_add_tail(&pi->list, &s->valid_paths);
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return 0;
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}
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static void st_fail_path(struct path_selector *ps, struct dm_path *path)
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{
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struct selector *s = ps->context;
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struct path_info *pi = path->pscontext;
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list_move(&pi->list, &s->failed_paths);
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}
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static int st_reinstate_path(struct path_selector *ps, struct dm_path *path)
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{
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struct selector *s = ps->context;
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struct path_info *pi = path->pscontext;
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list_move_tail(&pi->list, &s->valid_paths);
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return 0;
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}
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/*
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* Compare the estimated service time of 2 paths, pi1 and pi2,
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* for the incoming I/O.
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*
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* Returns:
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* < 0 : pi1 is better
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* 0 : no difference between pi1 and pi2
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* > 0 : pi2 is better
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*
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* Description:
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* Basically, the service time is estimated by:
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* ('pi->in-flight-size' + 'incoming') / 'pi->relative_throughput'
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* To reduce the calculation, some optimizations are made.
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* (See comments inline)
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*/
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static int st_compare_load(struct path_info *pi1, struct path_info *pi2,
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size_t incoming)
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{
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size_t sz1, sz2, st1, st2;
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sz1 = atomic_read(&pi1->in_flight_size);
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sz2 = atomic_read(&pi2->in_flight_size);
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/*
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* Case 1: Both have same throughput value. Choose less loaded path.
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*/
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if (pi1->relative_throughput == pi2->relative_throughput)
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return sz1 - sz2;
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/*
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* Case 2a: Both have same load. Choose higher throughput path.
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* Case 2b: One path has no throughput value. Choose the other one.
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*/
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if (sz1 == sz2 ||
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!pi1->relative_throughput || !pi2->relative_throughput)
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return pi2->relative_throughput - pi1->relative_throughput;
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/*
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* Case 3: Calculate service time. Choose faster path.
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* Service time using pi1:
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* st1 = (sz1 + incoming) / pi1->relative_throughput
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* Service time using pi2:
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* st2 = (sz2 + incoming) / pi2->relative_throughput
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*
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* To avoid the division, transform the expression to use
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* multiplication.
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* Because ->relative_throughput > 0 here, if st1 < st2,
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* the expressions below are the same meaning:
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* (sz1 + incoming) / pi1->relative_throughput <
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* (sz2 + incoming) / pi2->relative_throughput
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* (sz1 + incoming) * pi2->relative_throughput <
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* (sz2 + incoming) * pi1->relative_throughput
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* So use the later one.
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*/
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sz1 += incoming;
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sz2 += incoming;
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if (unlikely(sz1 >= ST_MAX_INFLIGHT_SIZE ||
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sz2 >= ST_MAX_INFLIGHT_SIZE)) {
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/*
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* Size may be too big for multiplying pi->relative_throughput
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* and overflow.
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* To avoid the overflow and mis-selection, shift down both.
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*/
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sz1 >>= ST_MAX_RELATIVE_THROUGHPUT_SHIFT;
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sz2 >>= ST_MAX_RELATIVE_THROUGHPUT_SHIFT;
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}
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st1 = sz1 * pi2->relative_throughput;
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st2 = sz2 * pi1->relative_throughput;
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if (st1 != st2)
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return st1 - st2;
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/*
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* Case 4: Service time is equal. Choose higher throughput path.
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*/
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return pi2->relative_throughput - pi1->relative_throughput;
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}
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static struct dm_path *st_select_path(struct path_selector *ps,
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unsigned *repeat_count, size_t nr_bytes)
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{
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struct selector *s = ps->context;
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struct path_info *pi = NULL, *best = NULL;
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if (list_empty(&s->valid_paths))
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return NULL;
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/* Change preferred (first in list) path to evenly balance. */
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list_move_tail(s->valid_paths.next, &s->valid_paths);
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list_for_each_entry(pi, &s->valid_paths, list)
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if (!best || (st_compare_load(pi, best, nr_bytes) < 0))
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best = pi;
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if (!best)
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return NULL;
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*repeat_count = best->repeat_count;
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return best->path;
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}
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static int st_start_io(struct path_selector *ps, struct dm_path *path,
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size_t nr_bytes)
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{
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struct path_info *pi = path->pscontext;
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atomic_add(nr_bytes, &pi->in_flight_size);
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return 0;
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}
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static int st_end_io(struct path_selector *ps, struct dm_path *path,
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size_t nr_bytes)
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{
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struct path_info *pi = path->pscontext;
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atomic_sub(nr_bytes, &pi->in_flight_size);
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return 0;
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}
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static struct path_selector_type st_ps = {
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.name = "service-time",
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.module = THIS_MODULE,
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.table_args = 2,
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.info_args = 2,
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.create = st_create,
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.destroy = st_destroy,
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.status = st_status,
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.add_path = st_add_path,
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.fail_path = st_fail_path,
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.reinstate_path = st_reinstate_path,
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.select_path = st_select_path,
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.start_io = st_start_io,
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.end_io = st_end_io,
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};
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static int __init dm_st_init(void)
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{
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int r = dm_register_path_selector(&st_ps);
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if (r < 0)
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DMERR("register failed %d", r);
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DMINFO("version " ST_VERSION " loaded");
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return r;
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}
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static void __exit dm_st_exit(void)
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{
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int r = dm_unregister_path_selector(&st_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_st_init);
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module_exit(dm_st_exit);
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MODULE_DESCRIPTION(DM_NAME " throughput oriented path selector");
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MODULE_AUTHOR("Kiyoshi Ueda <k-ueda@ct.jp.nec.com>");
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MODULE_LICENSE("GPL");
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