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