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Diffstat (limited to 'include/net/netdev_queues.h')
| -rw-r--r-- | include/net/netdev_queues.h | 173 |
1 files changed, 173 insertions, 0 deletions
diff --git a/include/net/netdev_queues.h b/include/net/netdev_queues.h new file mode 100644 index 000000000..8b8ed4e13 --- /dev/null +++ b/include/net/netdev_queues.h @@ -0,0 +1,173 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _LINUX_NET_QUEUES_H +#define _LINUX_NET_QUEUES_H + +#include <linux/netdevice.h> + +/** + * DOC: Lockless queue stopping / waking helpers. + * + * The netif_txq_maybe_stop() and __netif_txq_completed_wake() + * macros are designed to safely implement stopping + * and waking netdev queues without full lock protection. + * + * We assume that there can be no concurrent stop attempts and no concurrent + * wake attempts. The try-stop should happen from the xmit handler, + * while wake up should be triggered from NAPI poll context. + * The two may run concurrently (single producer, single consumer). + * + * The try-stop side is expected to run from the xmit handler and therefore + * it does not reschedule Tx (netif_tx_start_queue() instead of + * netif_tx_wake_queue()). Uses of the ``stop`` macros outside of the xmit + * handler may lead to xmit queue being enabled but not run. + * The waking side does not have similar context restrictions. + * + * The macros guarantee that rings will not remain stopped if there's + * space available, but they do *not* prevent false wake ups when + * the ring is full! Drivers should check for ring full at the start + * for the xmit handler. + * + * All descriptor ring indexes (and other relevant shared state) must + * be updated before invoking the macros. + */ + +#define netif_txq_try_stop(txq, get_desc, start_thrs) \ + ({ \ + int _res; \ + \ + netif_tx_stop_queue(txq); \ + /* Producer index and stop bit must be visible \ + * to consumer before we recheck. \ + * Pairs with a barrier in __netif_txq_completed_wake(). \ + */ \ + smp_mb__after_atomic(); \ + \ + /* We need to check again in a case another \ + * CPU has just made room available. \ + */ \ + _res = 0; \ + if (unlikely(get_desc >= start_thrs)) { \ + netif_tx_start_queue(txq); \ + _res = -1; \ + } \ + _res; \ + }) \ + +/** + * netif_txq_maybe_stop() - locklessly stop a Tx queue, if needed + * @txq: struct netdev_queue to stop/start + * @get_desc: get current number of free descriptors (see requirements below!) + * @stop_thrs: minimal number of available descriptors for queue to be left + * enabled + * @start_thrs: minimal number of descriptors to re-enable the queue, can be + * equal to @stop_thrs or higher to avoid frequent waking + * + * All arguments may be evaluated multiple times, beware of side effects. + * @get_desc must be a formula or a function call, it must always + * return up-to-date information when evaluated! + * Expected to be used from ndo_start_xmit, see the comment on top of the file. + * + * Returns: + * 0 if the queue was stopped + * 1 if the queue was left enabled + * -1 if the queue was re-enabled (raced with waking) + */ +#define netif_txq_maybe_stop(txq, get_desc, stop_thrs, start_thrs) \ + ({ \ + int _res; \ + \ + _res = 1; \ + if (unlikely(get_desc < stop_thrs)) \ + _res = netif_txq_try_stop(txq, get_desc, start_thrs); \ + _res; \ + }) \ + +/* Variant of netdev_tx_completed_queue() which guarantees smp_mb() if + * @bytes != 0, regardless of kernel config. + */ +static inline void +netdev_txq_completed_mb(struct netdev_queue *dev_queue, + unsigned int pkts, unsigned int bytes) +{ + if (IS_ENABLED(CONFIG_BQL)) + netdev_tx_completed_queue(dev_queue, pkts, bytes); + else if (bytes) + smp_mb(); +} + +/** + * __netif_txq_completed_wake() - locklessly wake a Tx queue, if needed + * @txq: struct netdev_queue to stop/start + * @pkts: number of packets completed + * @bytes: number of bytes completed + * @get_desc: get current number of free descriptors (see requirements below!) + * @start_thrs: minimal number of descriptors to re-enable the queue + * @down_cond: down condition, predicate indicating that the queue should + * not be woken up even if descriptors are available + * + * All arguments may be evaluated multiple times. + * @get_desc must be a formula or a function call, it must always + * return up-to-date information when evaluated! + * Reports completed pkts/bytes to BQL. + * + * Returns: + * 0 if the queue was woken up + * 1 if the queue was already enabled (or disabled but @down_cond is true) + * -1 if the queue was left unchanged (@start_thrs not reached) + */ +#define __netif_txq_completed_wake(txq, pkts, bytes, \ + get_desc, start_thrs, down_cond) \ + ({ \ + int _res; \ + \ + /* Report to BQL and piggy back on its barrier. \ + * Barrier makes sure that anybody stopping the queue \ + * after this point sees the new consumer index. \ + * Pairs with barrier in netif_txq_try_stop(). \ + */ \ + netdev_txq_completed_mb(txq, pkts, bytes); \ + \ + _res = -1; \ + if (pkts && likely(get_desc >= start_thrs)) { \ + _res = 1; \ + if (unlikely(netif_tx_queue_stopped(txq)) && \ + !(down_cond)) { \ + netif_tx_wake_queue(txq); \ + _res = 0; \ + } \ + } \ + _res; \ + }) + +#define netif_txq_completed_wake(txq, pkts, bytes, get_desc, start_thrs) \ + __netif_txq_completed_wake(txq, pkts, bytes, get_desc, start_thrs, false) + +/* subqueue variants follow */ + +#define netif_subqueue_try_stop(dev, idx, get_desc, start_thrs) \ + ({ \ + struct netdev_queue *txq; \ + \ + txq = netdev_get_tx_queue(dev, idx); \ + netif_txq_try_stop(txq, get_desc, start_thrs); \ + }) + +#define netif_subqueue_maybe_stop(dev, idx, get_desc, stop_thrs, start_thrs) \ + ({ \ + struct netdev_queue *txq; \ + \ + txq = netdev_get_tx_queue(dev, idx); \ + netif_txq_maybe_stop(txq, get_desc, stop_thrs, start_thrs); \ + }) + +#define netif_subqueue_completed_wake(dev, idx, pkts, bytes, \ + get_desc, start_thrs) \ + ({ \ + struct netdev_queue *txq; \ + \ + txq = netdev_get_tx_queue(dev, idx); \ + netif_txq_completed_wake(txq, pkts, bytes, \ + get_desc, start_thrs); \ + }) + +#endif |