301f227fc8
Drivers call netdev_tx_completed_queue() right before netif_txq_maybe_wake(). If BQL is enabled netdev_tx_completed_queue() should issue a memory barrier, so we can depend on that separating the stop check from the consumer index update, instead of adding another barrier in netif_txq_maybe_wake(). This matters more than the barriers on the xmit path, because the wake condition is almost always true. So we issue the consumer side barrier often. Wrap netdev_tx_completed_queue() in a local helper to issue the barrier even if BQL is disabled. Keep the same semantics as netdev_tx_completed_queue() (barrier only if bytes != 0) to make it clear that the barrier is conditional. Plus since macro gets pkt/byte counts as arguments now - we can skip waking if there were no packets completed. Signed-off-by: Jakub Kicinski <kuba@kernel.org>
164 lines
5.5 KiB
C
164 lines
5.5 KiB
C
/* 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); \
|
|
})
|
|
|
|
#endif
|