Re: [PATCH net] net: thunderbolt: Count delivered packets in rx_packets and rx_bytes

[Simon Horman <horms@kernel.org>]

On Sat, Aug 15, 2026 at 10:21:52AM +0000, Fan Ye via B4 Relay wrote:
> From: Fan Ye <fy15309206903@gmail.com>
> 
> tbnet_poll() increments rx_packets once per received frame because that is
> the NAPI work unit, and then adds the same number to stats.rx_packets. An
> skb is handed to the stack only when the last frame of a packet arrives,
> so once the MTU exceeds TBNET_MAX_PAYLOAD_SIZE the statistic reports
> frames. tx_packets is bumped once per skb, so the two ends of a link
> disagree: at MTU 65330 the receiver reports 16 times the packets its
> sender sent.
> 
> rx_bytes has the matching problem: frames of a packet that is later
> dropped mid-assembly are already accounted, so it does not correspond to
> rx_packets as documented. Account for both where the packet is completed,
> and leave the NAPI work counter alone.
> 
> Fixes: e69b6c02b4c3 ("net: Add support for networking over Thunderbolt cable")
> Assisted-by: Claude:claude-opus-5
> Signed-off-by: Fan Ye <fy15309206903@gmail.com>
> ---
> Seen at MTU 65330 on an ASM4242 host-to-host link, where a packet is 16
> frames. On the receiver rx_bytes/rx_packets came out at 4083.9, i.e.
> TBNET_MAX_PAYLOAD_SIZE, and rx_packets ran 15.9x the IP layer's InReceives;
> with the patch they are 65308.3 and 0.99. At the default MTU a packet fits
> in one frame and the counters already agree, which is why this went
> unnoticed.

Reviewed-by: Simon Horman <horms@kernel.org>