1 | /* SPDX-License-Identifier: GPL-2.0 */ |
2 | #ifndef _LINUX_NET_QUEUES_H |
3 | #define _LINUX_NET_QUEUES_H |
4 | |
5 | #include <linux/netdevice.h> |
6 | |
7 | /** |
8 | * DOC: Lockless queue stopping / waking helpers. |
9 | * |
10 | * The netif_txq_maybe_stop() and __netif_txq_completed_wake() |
11 | * macros are designed to safely implement stopping |
12 | * and waking netdev queues without full lock protection. |
13 | * |
14 | * We assume that there can be no concurrent stop attempts and no concurrent |
15 | * wake attempts. The try-stop should happen from the xmit handler, |
16 | * while wake up should be triggered from NAPI poll context. |
17 | * The two may run concurrently (single producer, single consumer). |
18 | * |
19 | * The try-stop side is expected to run from the xmit handler and therefore |
20 | * it does not reschedule Tx (netif_tx_start_queue() instead of |
21 | * netif_tx_wake_queue()). Uses of the ``stop`` macros outside of the xmit |
22 | * handler may lead to xmit queue being enabled but not run. |
23 | * The waking side does not have similar context restrictions. |
24 | * |
25 | * The macros guarantee that rings will not remain stopped if there's |
26 | * space available, but they do *not* prevent false wake ups when |
27 | * the ring is full! Drivers should check for ring full at the start |
28 | * for the xmit handler. |
29 | * |
30 | * All descriptor ring indexes (and other relevant shared state) must |
31 | * be updated before invoking the macros. |
32 | */ |
33 | |
34 | #define netif_txq_try_stop(txq, get_desc, start_thrs) \ |
35 | ({ \ |
36 | int _res; \ |
37 | \ |
38 | netif_tx_stop_queue(txq); \ |
39 | /* Producer index and stop bit must be visible \ |
40 | * to consumer before we recheck. \ |
41 | * Pairs with a barrier in __netif_txq_completed_wake(). \ |
42 | */ \ |
43 | smp_mb__after_atomic(); \ |
44 | \ |
45 | /* We need to check again in a case another \ |
46 | * CPU has just made room available. \ |
47 | */ \ |
48 | _res = 0; \ |
49 | if (unlikely(get_desc >= start_thrs)) { \ |
50 | netif_tx_start_queue(txq); \ |
51 | _res = -1; \ |
52 | } \ |
53 | _res; \ |
54 | }) \ |
55 | |
56 | /** |
57 | * netif_txq_maybe_stop() - locklessly stop a Tx queue, if needed |
58 | * @txq: struct netdev_queue to stop/start |
59 | * @get_desc: get current number of free descriptors (see requirements below!) |
60 | * @stop_thrs: minimal number of available descriptors for queue to be left |
61 | * enabled |
62 | * @start_thrs: minimal number of descriptors to re-enable the queue, can be |
63 | * equal to @stop_thrs or higher to avoid frequent waking |
64 | * |
65 | * All arguments may be evaluated multiple times, beware of side effects. |
66 | * @get_desc must be a formula or a function call, it must always |
67 | * return up-to-date information when evaluated! |
68 | * Expected to be used from ndo_start_xmit, see the comment on top of the file. |
69 | * |
70 | * Returns: |
71 | * 0 if the queue was stopped |
72 | * 1 if the queue was left enabled |
73 | * -1 if the queue was re-enabled (raced with waking) |
74 | */ |
75 | #define netif_txq_maybe_stop(txq, get_desc, stop_thrs, start_thrs) \ |
76 | ({ \ |
77 | int _res; \ |
78 | \ |
79 | _res = 1; \ |
80 | if (unlikely(get_desc < stop_thrs)) \ |
81 | _res = netif_txq_try_stop(txq, get_desc, start_thrs); \ |
82 | _res; \ |
83 | }) \ |
84 | |
85 | /* Variant of netdev_tx_completed_queue() which guarantees smp_mb() if |
86 | * @bytes != 0, regardless of kernel config. |
87 | */ |
88 | static inline void |
89 | netdev_txq_completed_mb(struct netdev_queue *dev_queue, |
90 | unsigned int pkts, unsigned int bytes) |
91 | { |
92 | if (IS_ENABLED(CONFIG_BQL)) |
93 | netdev_tx_completed_queue(dev_queue, pkts, bytes); |
94 | else if (bytes) |
95 | smp_mb(); |
96 | } |
97 | |
98 | /** |
99 | * __netif_txq_completed_wake() - locklessly wake a Tx queue, if needed |
100 | * @txq: struct netdev_queue to stop/start |
101 | * @pkts: number of packets completed |
102 | * @bytes: number of bytes completed |
103 | * @get_desc: get current number of free descriptors (see requirements below!) |
104 | * @start_thrs: minimal number of descriptors to re-enable the queue |
105 | * @down_cond: down condition, predicate indicating that the queue should |
106 | * not be woken up even if descriptors are available |
107 | * |
108 | * All arguments may be evaluated multiple times. |
109 | * @get_desc must be a formula or a function call, it must always |
110 | * return up-to-date information when evaluated! |
111 | * Reports completed pkts/bytes to BQL. |
112 | * |
113 | * Returns: |
114 | * 0 if the queue was woken up |
115 | * 1 if the queue was already enabled (or disabled but @down_cond is true) |
116 | * -1 if the queue was left unchanged (@start_thrs not reached) |
117 | */ |
118 | #define __netif_txq_completed_wake(txq, pkts, bytes, \ |
119 | get_desc, start_thrs, down_cond) \ |
120 | ({ \ |
121 | int _res; \ |
122 | \ |
123 | /* Report to BQL and piggy back on its barrier. \ |
124 | * Barrier makes sure that anybody stopping the queue \ |
125 | * after this point sees the new consumer index. \ |
126 | * Pairs with barrier in netif_txq_try_stop(). \ |
127 | */ \ |
128 | netdev_txq_completed_mb(txq, pkts, bytes); \ |
129 | \ |
130 | _res = -1; \ |
131 | if (pkts && likely(get_desc > start_thrs)) { \ |
132 | _res = 1; \ |
133 | if (unlikely(netif_tx_queue_stopped(txq)) && \ |
134 | !(down_cond)) { \ |
135 | netif_tx_wake_queue(txq); \ |
136 | _res = 0; \ |
137 | } \ |
138 | } \ |
139 | _res; \ |
140 | }) |
141 | |
142 | #define netif_txq_completed_wake(txq, pkts, bytes, get_desc, start_thrs) \ |
143 | __netif_txq_completed_wake(txq, pkts, bytes, get_desc, start_thrs, false) |
144 | |
145 | /* subqueue variants follow */ |
146 | |
147 | #define netif_subqueue_try_stop(dev, idx, get_desc, start_thrs) \ |
148 | ({ \ |
149 | struct netdev_queue *txq; \ |
150 | \ |
151 | txq = netdev_get_tx_queue(dev, idx); \ |
152 | netif_txq_try_stop(txq, get_desc, start_thrs); \ |
153 | }) |
154 | |
155 | #define netif_subqueue_maybe_stop(dev, idx, get_desc, stop_thrs, start_thrs) \ |
156 | ({ \ |
157 | struct netdev_queue *txq; \ |
158 | \ |
159 | txq = netdev_get_tx_queue(dev, idx); \ |
160 | netif_txq_maybe_stop(txq, get_desc, stop_thrs, start_thrs); \ |
161 | }) |
162 | |
163 | #define netif_subqueue_completed_wake(dev, idx, pkts, bytes, \ |
164 | get_desc, start_thrs) \ |
165 | ({ \ |
166 | struct netdev_queue *txq; \ |
167 | \ |
168 | txq = netdev_get_tx_queue(dev, idx); \ |
169 | netif_txq_completed_wake(txq, pkts, bytes, \ |
170 | get_desc, start_thrs); \ |
171 | }) |
172 | |
173 | #endif |
174 | |