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