Re: [PATCH net] net: stmmac: count XDP_PASS frames in rx_packets on the XSK zero-copy path

[Lorenzo Bianconi <lorenzo.bianconi@oss.qualcomm.com>]

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> In the AF_XDP zero-copy RX path, frames that the XDP program passes to
> the stack are handed over by stmmac_dispatch_skb_zc(). That function
> increments rx_pkt_n instead of rx_packets since
> commit 133466c3bbe1 ("net: stmmac: use per-queue 64 bit statistics where necessary").
> 
> stmmac_rx_zc() already adds every processed frame to rx_pkt_n, so each
> XDP_PASS frame is counted twice there, and rx_packets, which
> ndo_get_stats64() reports, never counts them: on a zero-copy queue
> rx_bytes grows with the passed frames while rx_packets stays still.
> 
> Count the frame in rx_packets, as the regular RX path and the code
> before that commit did.
> 
> Found while testing AF_XDP zero-copy on an ADSP-SC598 (adi-dwmac,
> 100 Mbit/s link): rx_pkt_n grew almost twice as fast as the frames the
> MAC delivered, while "ip -s link" counted almost none.
> 
> Tested on that board with a 6.18-based kernel, whose zero-copy RX
> accounting matches net. An AF_XDP zero-copy socket on queue 0 received
> frames of one EtherType while UDP traffic was passed to the stack. In a
> run with 60 s of traffic before the change, rx_pkt_n was 1.88 times the
> frames that reached the driver (MAC frames minus RX FIFO overflows) and
> "ip -s link" counted 55 RX packets. In the same test with the change,
> rx_pkt_n equals the frames that reached the driver and rx_packets equals
> the frames passed to the stack.
> 
> Fixes: 133466c3bbe1 ("net: stmmac: use per-queue 64 bit statistics where necessary")
> Signed-off-by: Anandu Padinhare <Anandu.Padinhare@electrifex.com>

Reviewed-by: Lorenzo Bianconi <lorenzo.bianconi@oss.qualcomm.com>

> ---
>  drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> index a2177777727e..f8dceafdda2d 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> @@ -5587,7 +5587,7 @@ static void stmmac_dispatch_skb_zc(struct stmmac_priv *priv, u32 queue,
>  	napi_gro_receive(&ch->rxtx_napi, skb);
>  
>  	u64_stats_update_begin(&rxq_stats->napi_syncp);
> -	u64_stats_inc(&rxq_stats->napi.rx_pkt_n);
> +	u64_stats_inc(&rxq_stats->napi.rx_packets);
>  	u64_stats_add(&rxq_stats->napi.rx_bytes, len);
>  	u64_stats_update_end(&rxq_stats->napi_syncp);
>  }
> 
> base-commit: f66469d9905b39d2c260a15d7d6db450f4db67c1
> 

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