Re: [PATCH net v3 2/4] gve: Fix backward stats when interface goes down or configuration is adjusted

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- [Medium] When XDP is attached, the new base snapshot counts XDP TX ring
  traffic only at teardown, so device-level netdev qstats tx-packets/tx-…

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gve: Fix backward stats when interface goes down or configuration is adjusted

This patch keeps baseline rtnl and qstats counters in gve_priv so that
device statistics do not go backwards across queue teardown. Ring counters
are folded into the base in gve_queues_mem_remove() and in
gve_rx_queue_stop(). gve_get_base_stats() now reports the saved values
instead of zeros.

> diff --git a/drivers/net/ethernet/google/gve/gve_main.c b/drivers/net/ethernet/google/gve/gve_main.c
> index 26fdd22644f4d..52c152a986eb7 100644
> --- a/drivers/net/ethernet/google/gve/gve_main.c
> +++ b/drivers/net/ethernet/google/gve/gve_main.c

[ ... ]

> @@ -646,6 +688,9 @@ static void gve_queues_mem_remove(struct gve_priv *priv)
>  	gve_get_curr_alloc_cfgs(priv, &tx_alloc_cfg, &rx_alloc_cfg);
>  
>  	spin_lock_bh(&priv->stats_lock);
> +	gve_get_ring_stats(priv, &priv->base_net_stats);
> +	gve_get_ring_err_stats(priv, &priv->base_ring_err_stats);
> +
>  	priv->tx = NULL;
>  	priv->rx = NULL;
>  	spin_unlock_bh(&priv->stats_lock);

[Severity: Medium]
With an XDP program attached, will the device-level qstats tx-packets and
tx-bytes jump forward on every ifdown or reconfiguration?

The TX loop in gve_get_ring_stats() goes up to gve_num_tx_queues(), and
that count includes the XDP TX rings:

    return priv->tx_cfg.num_queues + priv->tx_cfg.num_xdp_queues;

As a result, the full pkt_done/bytes_done history of the XDP TX rings
ends up in base_net_stats.tx_*. Those counters are updated by
gve_clean_xdp_done() and by the DQO XDP path.

While the interface is up, qstats never reads those rings live:

gve_queues_start()
    netif_set_real_num_tx_queues(dev, priv->tx_cfg.num_queues);

netdev_nl_stats_by_netdev()
    netdev_stat_queue_sum(netdev, 0, netdev->real_num_rx_queues, &rx_sum,
                          0, netdev->real_num_tx_queues, &tx_sum);

So gve_get_tx_queue_stats() is only called for the non-XDP TX queues. The
new gve_get_base_stats() returns only the saved snapshot.

The qstats device total therefore leaves out live XDP TX traffic. Then,
when gve_close() or gve_adjust_config() reaches gve_queues_mem_remove(),
all of that traffic shows up at once. gve_get_stats() counts the live XDP
rings the whole time, so rtnl and qstats report different totals while
the interface is up.

The netdev_stat_ops kernel-doc says get_base_stats "can also be used to
report any miscellaneous packets transferred outside of the main set of
queues used by the networking stack".

Should gve_get_base_stats() also add the live counters of
tx[tx_cfg.num_queues .. gve_num_tx_queues())? The other option is to
limit the teardown snapshot's TX loop to tx_cfg.num_queues.

> @@ -2844,12 +2901,22 @@ static void gve_get_base_stats(struct net_device *dev,
>  			       struct netdev_queue_stats_rx *rx,
>  			       struct netdev_queue_stats_tx *tx)
>  {

[ ... ]

> +	spin_lock_bh(&priv->stats_lock);
> +	rx->packets = base_stats->rx_packets;
> +	rx->bytes = base_stats->rx_bytes;
> +	rx->alloc_fail = base_err_stats->rx_alloc_fails;
>  
> -	tx->packets = 0;
> -	tx->bytes = 0;
> +	tx->packets = base_stats->tx_packets;
> +	tx->bytes = base_stats->tx_bytes;
> +	spin_unlock_bh(&priv->stats_lock);
>  }

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Sashiko AI review · https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20261023204706.3112215-1-hramamurthy%40google.com