netdev - Re: [PATCH net-next v11 11/23] ovpn: store tunnel and transport statistics

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Message-ID: <41d80bb3-0bcc-44da-a5f0-d933d7c0e85a@openvpn.net>
Date: Thu, 31 Oct 2024 14:12:44 +0100
From: Antonio Quartulli <antonio@...nvpn.net>
To: Sabrina Dubroca <sd@...asysnail.net>
Cc: Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, Donald Hunter <donald.hunter@...il.com>,
 Shuah Khan <shuah@...nel.org>, ryazanov.s.a@...il.com,
 Andrew Lunn <andrew@...n.ch>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH net-next v11 11/23] ovpn: store tunnel and transport
 statistics



On 31/10/2024 12:37, Sabrina Dubroca wrote:
> 2024-10-29, 11:47:24 +0100, Antonio Quartulli wrote:
>> @@ -136,6 +139,10 @@ void ovpn_decrypt_post(void *data, int ret)
>>   		goto drop;
>>   	}
>>   
>> +	/* increment RX stats */
>> +	ovpn_peer_stats_increment_rx(&peer->vpn_stats, skb->len);
>> +	ovpn_peer_stats_increment_rx(&peer->link_stats, orig_len);
> 
> [I don't know much about the userspace implementation, so maybe this
> is a silly question]
> 
> What's the value of keeping track of 2 separate stats if they are
> incremented exactly at the same time? Packet count will be the same,
> and the difference in bytes will be just measuring the encap overhead.
> 
> Should one of them be "packets/individual messages that get received
> over the UDP/TCP link" and the other "packets that get passed up to
> the stack"?

You're correct: link_stats if "received over the TCP/UDP socket", while 
vpn_stats if what is passing through the ovpn virtual device.

Packet count may not match though, for example when something happens 
between "received packet on the link" and "packet passed up to the 
device" (i.e. decryption error).

This makes me wonder why we increment them at the very same place....
link_stats should be increased upon RX from the socket, while vpn_stats 
just before delivery. I'll double check.

> 
> 
>> @@ -197,6 +206,8 @@ void ovpn_encrypt_post(void *data, int ret)
>>   		goto err;
>>   
>>   	skb_mark_not_on_list(skb);
>> +	ovpn_peer_stats_increment_tx(&peer->link_stats, skb->len);
>> +	ovpn_peer_stats_increment_tx(&peer->vpn_stats, orig_len);
>>   
>>   	switch (peer->sock->sock->sk->sk_protocol) {
>>   	case IPPROTO_UDP:
> 
> And on TX maybe something like "packets that the stack wants to send
> through the tunnel" and "packets that actually make it onto the
> UDP/TCP socket after encap/encrypt"?

Correct.

Same issue here. Increments should not happen back to back.


Thanks a lot for spotting these.

Regards,


> 

-- 
Antonio Quartulli
OpenVPN Inc.