1 // SPDX-License-Identifier: GPL-2.0-only
3  * Copyright (C) 2004-2005 IBM Corp.  All Rights Reserved.
4  * Copyright (C) 2006-2009 NEC Corporation.
6  * dm-queue-length.c
13  * queue-length path selector - choose a path with the least number of
14  * in-flight I/Os.
18 #include "dm-path-selector.h"
26 #define DM_MSG_PREFIX	"multipath queue-length"
40 	atomic_t		qlen;	/* the number of in-flight I/Os */
48 		INIT_LIST_HEAD(&s->valid_paths);  in alloc_selector()
49 		INIT_LIST_HEAD(&s->failed_paths);  in alloc_selector()
50 		spin_lock_init(&s->lock);  in alloc_selector()
61 		return -ENOMEM;  in ql_create()
63 	ps->context = s;  in ql_create()
72 		list_del(&pi->list);  in ql_free_paths()
79 	struct selector *s = ps->context;  in ql_destroy()
81 	ql_free_paths(&s->valid_paths);  in ql_destroy()
82 	ql_free_paths(&s->failed_paths);  in ql_destroy()
84 	ps->context = NULL;  in ql_destroy()
97 		pi = path->pscontext;  in ql_status()
101 			DMEMIT("%d ", atomic_read(&pi->qlen));  in ql_status()
104 			DMEMIT("%u ", pi->repeat_count);  in ql_status()
118 	struct selector *s = ps->context;  in ql_add_path()
130 		*error = "queue-length ps: incorrect number of arguments";  in ql_add_path()
131 		return -EINVAL;  in ql_add_path()
135 		*error = "queue-length ps: invalid repeat count";  in ql_add_path()
136 		return -EINVAL;  in ql_add_path()
147 		*error = "queue-length ps: Error allocating path information";  in ql_add_path()
148 		return -ENOMEM;  in ql_add_path()
151 	pi->path = path;  in ql_add_path()
152 	pi->repeat_count = repeat_count;  in ql_add_path()
153 	atomic_set(&pi->qlen, 0);  in ql_add_path()
155 	path->pscontext = pi;  in ql_add_path()
157 	spin_lock_irqsave(&s->lock, flags);  in ql_add_path()
158 	list_add_tail(&pi->list, &s->valid_paths);  in ql_add_path()
159 	spin_unlock_irqrestore(&s->lock, flags);  in ql_add_path()
166 	struct selector *s = ps->context;  in ql_fail_path()
167 	struct path_info *pi = path->pscontext;  in ql_fail_path()
170 	spin_lock_irqsave(&s->lock, flags);  in ql_fail_path()
171 	list_move(&pi->list, &s->failed_paths);  in ql_fail_path()
172 	spin_unlock_irqrestore(&s->lock, flags);  in ql_fail_path()
177 	struct selector *s = ps->context;  in ql_reinstate_path()
178 	struct path_info *pi = path->pscontext;  in ql_reinstate_path()
181 	spin_lock_irqsave(&s->lock, flags);  in ql_reinstate_path()
182 	list_move_tail(&pi->list, &s->valid_paths);  in ql_reinstate_path()
183 	spin_unlock_irqrestore(&s->lock, flags);  in ql_reinstate_path()
189  * Select a path having the minimum number of in-flight I/Os
193 	struct selector *s = ps->context;  in ql_select_path()
198 	spin_lock_irqsave(&s->lock, flags);  in ql_select_path()
199 	if (list_empty(&s->valid_paths))  in ql_select_path()
202 	list_for_each_entry(pi, &s->valid_paths, list) {  in ql_select_path()
204 		    (atomic_read(&pi->qlen) < atomic_read(&best->qlen)))  in ql_select_path()
207 		if (!atomic_read(&best->qlen))  in ql_select_path()
215 	list_move_tail(&best->list, &s->valid_paths);  in ql_select_path()
217 	ret = best->path;  in ql_select_path()
219 	spin_unlock_irqrestore(&s->lock, flags);  in ql_select_path()
226 	struct path_info *pi = path->pscontext;  in ql_start_io()
228 	atomic_inc(&pi->qlen);  in ql_start_io()
236 	struct path_info *pi = path->pscontext;  in ql_end_io()
238 	atomic_dec(&pi->qlen);  in ql_end_io()
244 	.name		= "queue-length",
285 	DM_NAME " path selector to balance the number of in-flight I/Os"