Re: [PATCH net-next v2 2/4] eth: mpnic: report per-queue stats

[netdev-bot+sashiko@kernel.org]

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- [Medium] This patch reports the RCQ `rcq.packets` and `rcq.bytes`
  counters as the netdev qstats `rx-packets` and `rx-bytes` attributes.

--

eth: mpnic: report per-queue stats

This commit exposes the per-ring packet and byte counters through the
netdev queue stats API. Counters for deactivated rings are reported
through the base stats.

> diff --git a/drivers/net/ethernet/meta/mpnic/mpnic_netdev.c b/drivers/net/ethernet/meta/mpnic/mpnic_netdev.c
> index 5164475a0f943..c2f4a326a8f0f 100644
> --- a/drivers/net/ethernet/meta/mpnic/mpnic_netdev.c
> +++ b/drivers/net/ethernet/meta/mpnic/mpnic_netdev.c

[ ... ]

> @@ -146,6 +147,77 @@ static const struct net_device_ops mpnic_netdev_ops = {
>  	.ndo_get_stats64	= mpnic_get_stats64,
>  };
>  
> +static void mpnic_get_queue_stats_rx(struct net_device *dev, int idx,
> +				     struct netdev_queue_stats_rx *rx)
> +{
> +	struct mpnic_net *mpn = netdev_priv(dev);
> +	struct mpnic_ring *rxr = mpn->rx[idx];
> +	struct mpnic_queue_stats *stats;
> +	unsigned int start;
> +	u64 bytes, packets;
> +
> +	if (!rxr)
> +		return;
> +
> +	stats = &rxr->stats;
> +	do {
> +		start = u64_stats_fetch_begin(&stats->syncp);
> +		bytes = u64_stats_read(&stats->rcq.bytes);
> +		packets = u64_stats_read(&stats->rcq.packets);
> +	} while (u64_stats_fetch_retry(&stats->syncp, start));
> +
> +	rx->bytes = bytes;
> +	rx->packets = packets;
> +}

[Severity: Medium]
Do rcq.packets and rcq.bytes match the qstats meaning of rx-packets and
rx-bytes?

The netdev.yaml spec defines rx-packets as "Number of wire packets
successfully received and passed to the stack". It defines rx-bytes as
"Successfully received bytes, see rx-packets".

In mpnic_clean_rcq() in mpnic_txrx.c, packets++ runs for every META
completion, including completions where the driver drops the packet:

drivers/net/ethernet/meta/mpnic/mpnic_txrx.c:mpnic_clean_rcq() {
    ...
			if (likely(!(rcd &
				     MPNIC_RCD_META_UNCORRECTABLE_ERR_MASK) &&
				   !state->pkt.add_frag_failed)) {
				bytes += xdp_get_buff_len(&state->pkt.buff);
				skb = xdp_build_skb_from_buff(&state->pkt.buff);
			}

			if (likely(skb)) {
				napi_gro_receive(&nv->napi, skb);
			} else {
				mpnic_put_pkt_buff(&state->pkt, true);
				if (rcd & MPNIC_RCD_META_UNCORRECTABLE_ERR_MASK)
					errors++;
				else
					dropped++;
			}

			state->pkt.buff.data_hard_start = NULL;
			packets++;
    ...
	u64_stats_add(&rcq->stats.rcq.packets, packets - errors);
	u64_stats_add(&rcq->stats.rcq.bytes, bytes);
	u64_stats_add(&rcq->stats.rcq.dropped, dropped);
    ...
}

Only errors are subtracted from packets. If add_frag_failed is set, or if
xdp_build_skb_from_buff() returns NULL, the packet is counted in dropped
and also in rx-packets.

The buffer length is also added to bytes before xdp_build_skb_from_buff()
runs. A failed skb build therefore still counts toward rx-bytes. An
add_frag_failed drop adds to packets but not to bytes, so the two
counters also disagree with each other.

mpnic_get_base_stats() reports the same values once
mpnic_aggregate_ring_rcq_counters() folds them into base->rx. The
miscount carries over after a ring is deactivated.

fbnic_clean_rcq() handles this by jumping to next_dont_count for dropped
packets, so they are counted in neither packets nor bytes. Could mpnic
do the same?

The counter semantics come from "eth: mpnic: count packets, bytes, and
drops per ring" earlier in this series. This patch is the one that
exposes them as qstats rx-packets and rx-bytes.

The later patch "eth: mpnic: count Rx allocation failures" also counts
skb build failures in alloc_failed. Those packets still stay in packets
and bytes.

[ ... ]

-- 
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