netdev - Re: [PATCH net-next v2 08/22] ovpn: implement basic TX path (UDP)

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Message-ID: <87ttlgrb86.fsf@toke.dk>
Date: Fri, 08 Mar 2024 16:31:53 +0100
From: Toke Høiland-Jørgensen <toke@...hat.com>
To: Antonio Quartulli <antonio@...nvpn.net>, netdev@...r.kernel.org
Cc: Jakub Kicinski <kuba@...nel.org>, Sergey Ryazanov
 <ryazanov.s.a@...il.com>, Paolo Abeni <pabeni@...hat.com>, Eric Dumazet
 <edumazet@...gle.com>, Antonio Quartulli <antonio@...nvpn.net>
Subject: Re: [PATCH net-next v2 08/22] ovpn: implement basic TX path (UDP)

Antonio Quartulli <antonio@...nvpn.net> writes:

> +/* send skb to connected peer, if any */
> +static void ovpn_queue_skb(struct ovpn_struct *ovpn, struct sk_buff *skb, struct ovpn_peer *peer)
> +{
> +	int ret;
> +
> +	if (likely(!peer))
> +		/* retrieve peer serving the destination IP of this packet */
> +		peer = ovpn_peer_lookup_by_dst(ovpn, skb);
> +	if (unlikely(!peer)) {
> +		net_dbg_ratelimited("%s: no peer to send data to\n", ovpn->dev->name);
> +		goto drop;
> +	}
> +
> +	ret = ptr_ring_produce_bh(&peer->tx_ring, skb);
> +	if (unlikely(ret < 0)) {
> +		net_err_ratelimited("%s: cannot queue packet to TX ring\n", peer->ovpn->dev->name);
> +		goto drop;
> +	}
> +
> +	if (!queue_work(ovpn->crypto_wq, &peer->encrypt_work))
> +		ovpn_peer_put(peer);
> +
> +	return;
> +drop:
> +	if (peer)
> +		ovpn_peer_put(peer);
> +	kfree_skb_list(skb);
> +}

So this puts packets on a per-peer 1024-packet FIFO queue with no
backpressure? That sounds like a pretty terrible bufferbloat situation.
Did you do any kind of latency-under-load testing of this, such as
running the RRUL test[0] through it?

-Toke

[0] https://flent.org/tests.html#the-realtime-response-under-load-rrul-test