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docs: net: clarify the NAPI rules around XDP Tx

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page pool and XDP should not be accessed from IRQ context
which may happen if drivers try to clean up XDP TX with
NAPI budget of 0.

Link: https://lore.kernel.org/r/20230720161323.2025379-1-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Jakub Kicinski 2023-07-20 09:13:23 -07:00
parent 57f1f9dd3a
commit 32ad45b769
1 changed files with 7 additions and 6 deletions
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13
Documentation/networking/napi.rst
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@ -65,15 +65,16 @@ argument - drivers can process completions for any number of Tx
packets but should only process up to ``budget`` number of
Rx packets. Rx processing is usually much more expensive.
In other words, it is recommended to ignore the budget argument when
performing TX buffer reclamation to ensure that the reclamation is not
arbitrarily bounded; however, it is required to honor the budget argument
for RX processing.
In other words for Rx processing the ``budget`` argument limits how many
packets driver can process in a single poll. Rx specific APIs like page
pool or XDP cannot be used at all when ``budget`` is 0.
skb Tx processing should happen regardless of the ``budget``, but if
the argument is 0 driver cannot call any XDP (or page pool) APIs.
.. warning::
The ``budget`` argument may be 0 if core tries to only process Tx completions
and no Rx packets.
The ``budget`` argument may be 0 if core tries to only process
skb Tx completions and no Rx or XDP packets.
The poll method returns the amount of work done. If the driver still
has outstanding work to do (e.g. ``budget`` was exhausted)