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362 lines
8.8 KiB
362 lines
8.8 KiB
/* |
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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 "0.3.0" |
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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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spinlock_t lock; |
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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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spin_lock_init(&s->lock); |
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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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unsigned long flags; |
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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 (repeat_count > 1) { |
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DMWARN_LIMIT("repeat_count > 1 is deprecated, using 1 instead"); |
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repeat_count = 1; |
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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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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 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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unsigned long flags; |
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spin_lock_irqsave(&s->lock, flags); |
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list_move(&pi->list, &s->failed_paths); |
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spin_unlock_irqrestore(&s->lock, flags); |
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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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unsigned long flags; |
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spin_lock_irqsave(&s->lock, flags); |
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list_move_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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/* |
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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, 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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struct dm_path *ret = NULL; |
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unsigned long flags; |
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spin_lock_irqsave(&s->lock, flags); |
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if (list_empty(&s->valid_paths)) |
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goto out; |
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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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goto out; |
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/* Move most recently used to least preferred to evenly balance. */ |
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list_move_tail(&best->list, &s->valid_paths); |
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ret = best->path; |
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out: |
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spin_unlock_irqrestore(&s->lock, flags); |
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return ret; |
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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, u64 start_time) |
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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 <[email protected]>"); |
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MODULE_LICENSE("GPL");
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