netdev - Re: [PATCH net-next v2 06/22] ovpn: introduce the ovpn

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Date: Mon, 4 Mar 2024 23:56:59 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Antonio Quartulli <antonio@...nvpn.net>
Cc: netdev@...r.kernel.org, Jakub Kicinski <kuba@...nel.org>,
	Sergey Ryazanov <ryazanov.s.a@...il.com>,
	Paolo Abeni <pabeni@...hat.com>, Eric Dumazet <edumazet@...gle.com>
Subject: Re: [PATCH net-next v2 06/22] ovpn: introduce the ovpn_peer object

> +	ret = ptr_ring_init(&peer->tx_ring, OVPN_QUEUE_LEN, GFP_KERNEL);
> +	if (ret < 0) {
> +		netdev_err(ovpn->dev, "%s: cannot allocate TX ring\n", __func__);
> +		goto err_dst_cache;
> +	}
> +
> +	ret = ptr_ring_init(&peer->rx_ring, OVPN_QUEUE_LEN, GFP_KERNEL);
> +	if (ret < 0) {
> +		netdev_err(ovpn->dev, "%s: cannot allocate RX ring\n", __func__);
> +		goto err_tx_ring;
> +	}
> +
> +	ret = ptr_ring_init(&peer->netif_rx_ring, OVPN_QUEUE_LEN, GFP_KERNEL);
> +	if (ret < 0) {
> +		netdev_err(ovpn->dev, "%s: cannot allocate NETIF RX ring\n", __func__);
> +		goto err_rx_ring;
> +	}

These rings are 1024 entries? The real netif below also likely has
another 1024 entry ring. Rings like this are latency. Is there a BQL
like mechanism to actually keep the rings empty, throw packets away
rather than queue them, because queueing them just accumulates
latency?

So, i guess my question is, how do you avoid bufferbloat? Why do you
actually need these rings?

    Andrew