netdev - Re: [PATCH net-next v2 03/10] tun: switch to net core provided statistics counters

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Message-ID: <dcb51de1-5e11-7c07-9784-bf3546a1246a@gmail.com>
Date:   Fri, 6 Nov 2020 08:48:48 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>,
        Willem de Bruijn <willemb@...gle.com>
Cc:     David Miller <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Harald Welte <laforge@...monks.org>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        osmocom-net-gprs@...ts.osmocom.org, wireguard@...ts.zx2c4.com,
        Steffen Klassert <steffen.klassert@...unet.com>
Subject: Re: [PATCH net-next v2 03/10] tun: switch to net core provided
 statistics counters

On 06.11.2020 02:14, Jakub Kicinski wrote:
> On Wed, 4 Nov 2020 15:25:24 +0100 Heiner Kallweit wrote:
>> @@ -1066,7 +1054,7 @@ static netdev_tx_t tun_net_xmit(struct sk_buff *skb, struct net_device *dev)
>>  	return NETDEV_TX_OK;
>>  
>>  drop:
>> -	this_cpu_inc(tun->pcpu_stats->tx_dropped);
>> +	dev->stats.tx_dropped++;
>>  	skb_tx_error(skb);
>>  	kfree_skb(skb);
>>  	rcu_read_unlock();
> 
> This is no longer atomic. Multiple CPUs may try to update it at the
> same time.
> 
> Do you know what the story on dev->rx_dropped is? The kdoc says drivers
> are not supposed to use it but:
> 
> drivers/net/ipvlan/ipvlan_core.c:               atomic_long_inc(&skb->dev->rx_dropped);
> drivers/net/macvlan.c:  atomic_long_inc(&skb->dev->rx_dropped);
> drivers/net/vxlan.c:            atomic_long_inc(&vxlan->dev->rx_dropped);
> 
> Maybe tun can use it, too?
> 
Thanks, yes that should be possible. Here we speak about tx_dropped,
but AFAICS the same applies as for rx_dropped. Will change it accordingly
in a v3.