RE: [PATCH] mlx4: give precise rx/tx bytes/packets counters

[David Laight <David.Laight@ACULAB.COM>]

From: Of Eric Dumazet
> Sent: 25 November 2016 15:46
> mlx4 stats are chaotic because a deferred work queue is responsible
> to update them every 250 ms.
> 
> Even sampling stats every one second with "sar -n DEV 1" gives
> variations like the following :
...
> This patch allows rx/tx bytes/packets counters being folded at the
> time we need stats.
> 
> We now can fetch stats every 1 ms if we want to check NIC behavior
> on a small time window. It is also easier to detect anomalies.
...
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Cc: Tariq Toukan <tariqt@mellanox.com>
...
>  	for (i = 0; i < priv->rx_ring_num; i++) {
> -		stats->rx_packets += priv->rx_ring[i]->packets;
> -		stats->rx_bytes += priv->rx_ring[i]->bytes;
> -		sw_rx_dropped += priv->rx_ring[i]->dropped;
> -		priv->port_stats.rx_chksum_good += priv->rx_ring[i]->csum_ok;
> -		priv->port_stats.rx_chksum_none += priv->rx_ring[i]->csum_none;
> -		priv->port_stats.rx_chksum_complete += priv->rx_ring[i]->csum_complete;
> -		priv->xdp_stats.rx_xdp_drop    += priv->rx_ring[i]->xdp_drop;
> -		priv->xdp_stats.rx_xdp_tx      += priv->rx_ring[i]->xdp_tx;
> -		priv->xdp_stats.rx_xdp_tx_full += priv->rx_ring[i]->xdp_tx_full;
> +		const struct mlx4_en_rx_ring *ring = priv->rx_ring[i];
> +
> +		sw_rx_dropped			+= READ_ONCE(ring->dropped);
> +		priv->port_stats.rx_chksum_good += READ_ONCE(ring->csum_ok);
> +		priv->port_stats.rx_chksum_none += READ_ONCE(ring->csum_none);
> +		priv->port_stats.rx_chksum_complete += READ_ONCE(ring->csum_complete);
> +		priv->xdp_stats.rx_xdp_drop	+= READ_ONCE(ring->xdp_drop);
> +		priv->xdp_stats.rx_xdp_tx	+= READ_ONCE(ring->xdp_tx);
> +		priv->xdp_stats.rx_xdp_tx_full	+= READ_ONCE(ring->xdp_tx_full);

This chunk (and the one after) seem to be adding READ_ONCE() and don't
seem to be related to the commit message.

	David