linux-kernel - Re: [PATCH net] veth: fix ethtool statistical errors

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Date:   Fri, 17 Nov 2023 10:25:47 +0100
From:   Lorenzo Bianconi <lorenzo@...nel.org>
To:     Albert Huang <huangjie.albert@...edance.com>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Toshiaki Makita <toshiaki.makita1@...il.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] veth: fix ethtool statistical errors

> if peer->real_num_rx_queues > 1, the ethtool -s command for
> veth network device will display some error statistical values.
> The value of tx_idx is reset with each iteration, so even if
> peer->real_num_rx_queues is greater than 1, the value of tx_idx
> will remain constant. This results in incorrect statistical values.
> To fix this issue, assign the value of pp_idx to tx_idx.
> 
> Fixes: 5fe6e56776ba ("veth: rely on peer veth_rq for ndo_xdp_xmit accounting")
> Signed-off-by: Albert Huang <huangjie.albert@...edance.com>
> ---
>  drivers/net/veth.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/veth.c b/drivers/net/veth.c
> index 0deefd1573cf..3a8e3fc5eeb5 100644
> --- a/drivers/net/veth.c
> +++ b/drivers/net/veth.c
> @@ -225,7 +225,7 @@ static void veth_get_ethtool_stats(struct net_device *dev,
>  	for (i = 0; i < peer->real_num_rx_queues; i++) {
>  		const struct veth_rq_stats *rq_stats = &rcv_priv->rq[i].stats;
>  		const void *base = (void *)&rq_stats->vs;
> -		unsigned int start, tx_idx = idx;
> +		unsigned int start, tx_idx = pp_idx;
>  		size_t offset;
>  
>  		tx_idx += (i % dev->real_num_tx_queues) * VETH_TQ_STATS_LEN;
> -- 
> 2.20.1
> 

Hi Albert,

Can you please provide more details about the issue you are facing?
In particular, what is the number of configured tx and rx queues for both
peers?
tx_idx is the index of the current (local) tx queue and it must restart from
idx in each iteration otherwise we will have an issue when
peer->real_num_rx_queues is greater than dev->real_num_tx_queues.

Regards,
Lorenzo

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