RE: [PATCH net] docs: net: clarify the NAPI rules around XDP Tx

[Wei Fang <wei.fang@nxp.com>]

> -----Original Message-----
> From: Jakub Kicinski <kuba@kernel.org>
> Sent: 2023年7月21日 0:13
> To: davem@davemloft.net
> Cc: netdev@vger.kernel.org; edumazet@google.com; pabeni@redhat.com;
> Jakub Kicinski <kuba@kernel.org>; corbet@lwn.net; linux-doc@vger.kernel.org
> Subject: [PATCH net] docs: net: clarify the NAPI rules around XDP Tx
> 
> 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.
> 
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>
> ---
> CC: corbet@lwn.net
> CC: linux-doc@vger.kernel.org
> ---
>  Documentation/networking/napi.rst | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/Documentation/networking/napi.rst
> b/Documentation/networking/napi.rst
> index a7a047742e93..7bf7b95c4f7a 100644
> --- a/Documentation/networking/napi.rst
> +++ b/Documentation/networking/napi.rst
> @@ -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.
> 
Can I ask a stupid question why tx processing cannot call any XDP (or page pool)
APIs if the "budget" is 0?