summaryrefslogtreecommitdiff
path: root/lib/lwq.c
blob: 57d080a4d53d7078ef3f2dad76b2bb48c4c7c6a3 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
// SPDX-License-Identifier: GPL-2.0-only
/*
 * Light-weight single-linked queue.
 *
 * Entries are enqueued to the head of an llist, with no blocking.
 * This can happen in any context.
 *
 * Entries are dequeued using a spinlock to protect against multiple
 * access.  The llist is staged in reverse order, and refreshed
 * from the llist when it exhausts.
 *
 * This is particularly suitable when work items are queued in BH or
 * IRQ context, and where work items are handled one at a time by
 * dedicated threads.
 */
#include <linux/rcupdate.h>
#include <linux/lwq.h>

struct llist_node *__lwq_dequeue(struct lwq *q)
{
	struct llist_node *this;

	if (lwq_empty(q))
		return NULL;
	spin_lock(&q->lock);
	this = q->ready;
	if (!this && !llist_empty(&q->new)) {
		/* ensure queue doesn't appear transiently lwq_empty */
		smp_store_release(&q->ready, (void *)1);
		this = llist_reverse_order(llist_del_all(&q->new));
		if (!this)
			q->ready = NULL;
	}
	if (this)
		q->ready = llist_next(this);
	spin_unlock(&q->lock);
	return this;
}
EXPORT_SYMBOL_GPL(__lwq_dequeue);

/**
 * lwq_dequeue_all - dequeue all currently enqueued objects
 * @q:	the queue to dequeue from
 *
 * Remove and return a linked list of llist_nodes of all the objects that were
 * in the queue. The first on the list will be the object that was least
 * recently enqueued.
 */
struct llist_node *lwq_dequeue_all(struct lwq *q)
{
	struct llist_node *r, *t, **ep;

	if (lwq_empty(q))
		return NULL;

	spin_lock(&q->lock);
	r = q->ready;
	q->ready = NULL;
	t = llist_del_all(&q->new);
	spin_unlock(&q->lock);
	ep = &r;
	while (*ep)
		ep = &(*ep)->next;
	*ep = llist_reverse_order(t);
	return r;
}
EXPORT_SYMBOL_GPL(lwq_dequeue_all);

#if IS_ENABLED(CONFIG_LWQ_TEST)

#include <linux/module.h>
#include <linux/slab.h>
#include <linux/wait_bit.h>
#include <linux/kthread.h>
#include <linux/delay.h>
struct tnode {
	struct lwq_node n;
	int i;
	int c;
};

static int lwq_exercise(void *qv)
{
	struct lwq *q = qv;
	int cnt;
	struct tnode *t;

	for (cnt = 0; cnt < 10000; cnt++) {
		wait_var_event(q, (t = lwq_dequeue(q, struct tnode, n)) != NULL);
		t->c++;
		if (lwq_enqueue(&t->n, q))
			wake_up_var(q);
	}
	while (!kthread_should_stop())
		schedule_timeout_idle(1);
	return 0;
}

static int lwq_test(void)
{
	int i;
	struct lwq q;
	struct llist_node *l, **t1, *t2;
	struct tnode *t;
	struct task_struct *threads[8];

	printk(KERN_INFO "testing lwq....\n");
	lwq_init(&q);
	printk(KERN_INFO " lwq: run some threads\n");
	for (i = 0; i < ARRAY_SIZE(threads); i++)
		threads[i] = kthread_run(lwq_exercise, &q, "lwq-test-%d", i);
	for (i = 0; i < 100; i++) {
		t = kmalloc(sizeof(*t), GFP_KERNEL);
		if (!t)
			break;
		t->i = i;
		t->c = 0;
		if (lwq_enqueue(&t->n, &q))
			wake_up_var(&q);
	}
	/* wait for threads to exit */
	for (i = 0; i < ARRAY_SIZE(threads); i++)
		if (!IS_ERR_OR_NULL(threads[i]))
			kthread_stop(threads[i]);
	printk(KERN_INFO " lwq: dequeue first 50:");
	for (i = 0; i < 50 ; i++) {
		if (i && (i % 10) == 0) {
			printk(KERN_CONT "\n");
			printk(KERN_INFO " lwq: ... ");
		}
		t = lwq_dequeue(&q, struct tnode, n);
		if (t)
			printk(KERN_CONT " %d(%d)", t->i, t->c);
		kfree(t);
	}
	printk(KERN_CONT "\n");
	l = lwq_dequeue_all(&q);
	printk(KERN_INFO " lwq: delete the multiples of 3 (test lwq_for_each_safe())\n");
	lwq_for_each_safe(t, t1, t2, &l, n) {
		if ((t->i % 3) == 0) {
			t->i = -1;
			kfree(t);
			t = NULL;
		}
	}
	if (l)
		lwq_enqueue_batch(l, &q);
	printk(KERN_INFO " lwq: dequeue remaining:");
	while ((t = lwq_dequeue(&q, struct tnode, n)) != NULL) {
		printk(KERN_CONT " %d", t->i);
		kfree(t);
	}
	printk(KERN_CONT "\n");
	return 0;
}

module_init(lwq_test);
#endif /* CONFIG_LWQ_TEST*/