Root/net/rds/ib_ring.c

1/*
2 * Copyright (c) 2006 Oracle. All rights reserved.
3 *
4 * This software is available to you under a choice of one of two
5 * licenses. You may choose to be licensed under the terms of the GNU
6 * General Public License (GPL) Version 2, available from the file
7 * COPYING in the main directory of this source tree, or the
8 * OpenIB.org BSD license below:
9 *
10 * Redistribution and use in source and binary forms, with or
11 * without modification, are permitted provided that the following
12 * conditions are met:
13 *
14 * - Redistributions of source code must retain the above
15 * copyright notice, this list of conditions and the following
16 * disclaimer.
17 *
18 * - Redistributions in binary form must reproduce the above
19 * copyright notice, this list of conditions and the following
20 * disclaimer in the documentation and/or other materials
21 * provided with the distribution.
22 *
23 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
24 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
25 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
26 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
27 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
28 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
29 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
30 * SOFTWARE.
31 *
32 */
33#include <linux/kernel.h>
34
35#include "rds.h"
36#include "ib.h"
37
38/*
39 * Locking for IB rings.
40 * We assume that allocation is always protected by a mutex
41 * in the caller (this is a valid assumption for the current
42 * implementation).
43 *
44 * Freeing always happens in an interrupt, and hence only
45 * races with allocations, but not with other free()s.
46 *
47 * The interaction between allocation and freeing is that
48 * the alloc code has to determine the number of free entries.
49 * To this end, we maintain two counters; an allocation counter
50 * and a free counter. Both are allowed to run freely, and wrap
51 * around.
52 * The number of used entries is always (alloc_ctr - free_ctr) % NR.
53 *
54 * The current implementation makes free_ctr atomic. When the
55 * caller finds an allocation fails, it should set an "alloc fail"
56 * bit and retry the allocation. The "alloc fail" bit essentially tells
57 * the CQ completion handlers to wake it up after freeing some
58 * more entries.
59 */
60
61/*
62 * This only happens on shutdown.
63 */
64DECLARE_WAIT_QUEUE_HEAD(rds_ib_ring_empty_wait);
65
66void rds_ib_ring_init(struct rds_ib_work_ring *ring, u32 nr)
67{
68    memset(ring, 0, sizeof(*ring));
69    ring->w_nr = nr;
70    rdsdebug("ring %p nr %u\n", ring, ring->w_nr);
71}
72
73static inline u32 __rds_ib_ring_used(struct rds_ib_work_ring *ring)
74{
75    u32 diff;
76
77    /* This assumes that atomic_t has at least as many bits as u32 */
78    diff = ring->w_alloc_ctr - (u32) atomic_read(&ring->w_free_ctr);
79    BUG_ON(diff > ring->w_nr);
80
81    return diff;
82}
83
84void rds_ib_ring_resize(struct rds_ib_work_ring *ring, u32 nr)
85{
86    /* We only ever get called from the connection setup code,
87     * prior to creating the QP. */
88    BUG_ON(__rds_ib_ring_used(ring));
89    ring->w_nr = nr;
90}
91
92static int __rds_ib_ring_empty(struct rds_ib_work_ring *ring)
93{
94    return __rds_ib_ring_used(ring) == 0;
95}
96
97u32 rds_ib_ring_alloc(struct rds_ib_work_ring *ring, u32 val, u32 *pos)
98{
99    u32 ret = 0, avail;
100
101    avail = ring->w_nr - __rds_ib_ring_used(ring);
102
103    rdsdebug("ring %p val %u next %u free %u\n", ring, val,
104         ring->w_alloc_ptr, avail);
105
106    if (val && avail) {
107        ret = min(val, avail);
108        *pos = ring->w_alloc_ptr;
109
110        ring->w_alloc_ptr = (ring->w_alloc_ptr + ret) % ring->w_nr;
111        ring->w_alloc_ctr += ret;
112    }
113
114    return ret;
115}
116
117void rds_ib_ring_free(struct rds_ib_work_ring *ring, u32 val)
118{
119    ring->w_free_ptr = (ring->w_free_ptr + val) % ring->w_nr;
120    atomic_add(val, &ring->w_free_ctr);
121
122    if (__rds_ib_ring_empty(ring) &&
123        waitqueue_active(&rds_ib_ring_empty_wait))
124        wake_up(&rds_ib_ring_empty_wait);
125}
126
127void rds_ib_ring_unalloc(struct rds_ib_work_ring *ring, u32 val)
128{
129    ring->w_alloc_ptr = (ring->w_alloc_ptr - val) % ring->w_nr;
130    ring->w_alloc_ctr -= val;
131}
132
133int rds_ib_ring_empty(struct rds_ib_work_ring *ring)
134{
135    return __rds_ib_ring_empty(ring);
136}
137
138int rds_ib_ring_low(struct rds_ib_work_ring *ring)
139{
140    return __rds_ib_ring_used(ring) <= (ring->w_nr >> 1);
141}
142
143/*
144 * returns the oldest alloced ring entry. This will be the next one
145 * freed. This can't be called if there are none allocated.
146 */
147u32 rds_ib_ring_oldest(struct rds_ib_work_ring *ring)
148{
149    return ring->w_free_ptr;
150}
151
152/*
153 * returns the number of completed work requests.
154 */
155
156u32 rds_ib_ring_completed(struct rds_ib_work_ring *ring, u32 wr_id, u32 oldest)
157{
158    u32 ret;
159
160    if (oldest <= (unsigned long long)wr_id)
161        ret = (unsigned long long)wr_id - oldest + 1;
162    else
163        ret = ring->w_nr - oldest + (unsigned long long)wr_id + 1;
164
165    rdsdebug("ring %p ret %u wr_id %u oldest %u\n", ring, ret,
166         wr_id, oldest);
167    return ret;
168}
169

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