netdev - Re: [PATCH net-next RFC] net: x25: Queue received packets in the drivers instead of per-CPU queues

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Date:   Tue, 09 Mar 2021 14:23:41 +0100
From:   Martin Schiller <ms@....tdt.de>
To:     Xie He <xie.he.0141@...il.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Krzysztof Halasa <khc@...waw.pl>, linux-x25@...r.kernel.org,
        netdev@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next RFC] net: x25: Queue received packets in the
 drivers instead of per-CPU queues

On 2021-03-05 06:43, Xie He wrote:
> X.25 Layer 3 (the Packet Layer) expects layer 2 to provide a reliable
> datalink service such that no packets are reordered or dropped. And
> X.25 Layer 2 (the LAPB layer) is indeed designed to provide such 
> service.
> 
> However, this reliability is not preserved when a driver calls 
> "netif_rx"
> to deliver the received packets to layer 3, because "netif_rx" will put
> the packets into per-CPU queues before they are delivered to layer 3.
> If there are multiple CPUs, the order of the packets may not be 
> preserved.
> The per-CPU queues may also drop packets if there are too many.
> 
> Therefore, we should not call "netif_rx" to let it queue the packets.
> Instead, we should use our own queue that won't reorder or drop 
> packets.
> 
> This patch changes all X.25 drivers to use their own queues instead of
> calling "netif_rx". The patch also documents this requirement in the
> "x25-iface" documentation.

I've tested the hdlc_x25 driver.
Looks good to me.

Acked-by: Martin Schiller <ms@....tdt.de>