netdev - Re: [RFC PATCH 01/13] net: dsa: add plumbing for custom netdev statistics

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Message-ID: <20201018094951.0016f208@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Sun, 18 Oct 2020 09:49:51 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     netdev@...r.kernel.org, andrew@...n.ch, f.fainelli@...il.com,
        vivien.didelot@...il.com, Christian Eggers <ceggers@...i.de>,
        Kurt Kanzenbach <kurt@...utronix.de>
Subject: Re: [RFC PATCH 01/13] net: dsa: add plumbing for custom netdev
 statistics

On Sun, 18 Oct 2020 00:35:59 +0300 Vladimir Oltean wrote:
> DSA needs to push a header onto every packet on TX, and this might cause
> reallocation under certain scenarios, which might affect, for example,
> performance.
> 
> But reallocated packets are not standardized in struct pcpu_sw_netstats,
> struct net_device_stats or anywhere else, it seems, so we need to roll
> our own extra netdevice statistics and expose them to ethtool.
> 
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>

Could you consider adding "driver" stats under RTM_GETSTATS, 
or a similar new structured interface over ethtool?

Looks like the statistic in question has pretty clear semantics,
and may be more broadly useful.

> +/* Driver statistics, other than those in struct rtnl_link_stats64.
> + * These are collected per-CPU and aggregated by ethtool.
> + */
> +struct dsa_slave_stats {
> +	__u64			tx_reallocs;

s/__u/u/

> +	struct u64_stats_sync	syncp;
> +} __aligned(1 * sizeof(u64));

Why aligned to u64? Compiler should pick a reasonable alignment here 
by itself.