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Author	SHA1	Message	Date
Heiner Kallweit	cb18e5595d	net: add macro netif_subqueue_completed_wake Add netif_subqueue_completed_wake, complementing the subqueue versions netif_subqueue_try_stop and netif_subqueue_maybe_stop. Reviewed-by: Jacob Keller <jacob.e.keller@intel.com> Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com> Signed-off-by: Paolo Abeni <pabeni@redhat.com>	2023-04-18 12:59:01 +02:00
Jakub Kicinski	301f227fc8	net: piggy back on the memory barrier in bql when waking queues 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>	2023-04-10 17:56:18 -07:00
Jakub Kicinski	c91c46de6b	net: provide macros for commonly copied lockless queue stop/wake code A lot of drivers follow the same scheme to stop / start queues without introducing locks between xmit and NAPI tx completions. I'm guessing they all copy'n'paste each other's code. The original code dates back all the way to e1000 and Linux 2.6.19. Smaller drivers shy away from the scheme and introduce a lock which may cause deadlocks in netpoll. Provide macros which encapsulate the necessary logic. The macros do not prevent false wake ups, the extra barrier required to close that race is not worth it. See discussion in: https://lore.kernel.org/all/c39312a2-4537-14b4-270c-9fe1fbb91e89@gmail.com/ Acked-by: Herbert Xu <herbert@gondor.apana.org.au> Signed-off-by: Jakub Kicinski <kuba@kernel.org>	2023-04-10 17:56:18 -07:00

Author

SHA1

Message

Date

Heiner Kallweit

cb18e5595d

net: add macro netif_subqueue_completed_wake

Add netif_subqueue_completed_wake, complementing the subqueue versions
netif_subqueue_try_stop and netif_subqueue_maybe_stop.

Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

2023-04-18 12:59:01 +02:00

Jakub Kicinski

301f227fc8

net: piggy back on the memory barrier in bql when waking queues

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>

2023-04-10 17:56:18 -07:00

Jakub Kicinski

c91c46de6b

net: provide macros for commonly copied lockless queue stop/wake code

A lot of drivers follow the same scheme to stop / start queues
without introducing locks between xmit and NAPI tx completions.
I'm guessing they all copy'n'paste each other's code.
The original code dates back all the way to e1000 and Linux 2.6.19.

Smaller drivers shy away from the scheme and introduce a lock
which may cause deadlocks in netpoll.

Provide macros which encapsulate the necessary logic.

The macros do not prevent false wake ups, the extra barrier
required to close that race is not worth it. See discussion in:
https://lore.kernel.org/all/c39312a2-4537-14b4-270c-9fe1fbb91e89@gmail.com/

Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

2023-04-10 17:56:18 -07:00

3 Commits