netdev - Re: [PATCH net-next 3/3] net: xilinx: axienet: Add statistics support

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Message-ID: <40cff9a6-bad3-4f85-8cbc-6d4bc72f9b9f@lunn.ch>
Date: Tue, 11 Jun 2024 02:26:47 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Sean Anderson <sean.anderson@...ux.dev>
Cc: Radhey Shyam Pandey <radhey.shyam.pandey@....com>,
	netdev@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Michal Simek <michal.simek@....com>,
	Jakub Kicinski <kuba@...nel.org>,
	Russell King <linux@...linux.org.uk>,
	Paolo Abeni <pabeni@...hat.com>, Eric Dumazet <edumazet@...gle.com>,
	linux-kernel@...r.kernel.org,
	"David S . Miller" <davem@...emloft.net>
Subject: Re: [PATCH net-next 3/3] net: xilinx: axienet: Add statistics support

> +static u64 axienet_stat(struct axienet_local *lp, enum temac_stat stat)
> +{
> +	return u64_stats_read(&lp->hw_stats[stat]);
> +}
> @@ -1695,6 +1760,35 @@ axienet_get_stats64(struct net_device *dev, struct rtnl_link_stats64 *stats)
>  		stats->tx_packets = u64_stats_read(&lp->tx_packets);
>  		stats->tx_bytes = u64_stats_read(&lp->tx_bytes);
>  	} while (u64_stats_fetch_retry(&lp->tx_stat_sync, start));
> +
> +	if (!(lp->features & XAE_FEATURE_STATS))
> +		return;
> +
> +	do {
> +		start = u64_stats_fetch_begin(&lp->hw_stat_sync);
> +		stats->rx_length_errors =
> +			axienet_stat(lp, STAT_RX_LENGTH_ERRORS);

I'm i reading this correctly. You are returning the counters from the
last refresh period. What is that? 2.5Gbps would wrapper around a 32
byte counter in 13 seconds. I hope these statistics are not 13 seconds
out of date?

Since axienet_stats_update() also uses the lp->hw_stat_sync, i don't
see why you cannot read the hardware counter value and update to the
latest value.

       Andrew