netdev - Re: [Cake] [PATCH net-next v14 6/7] sch_cake: Add overhead compensation support to the rate shaper

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Message-ID: <20180521234513.GH26212@localhost.localdomain>
Date:   Mon, 21 May 2018 20:45:13 -0300
From:   Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
To:     Toke Høiland-Jørgensen <toke@...e.dk>
Cc:     netdev@...r.kernel.org, cake@...ts.bufferbloat.net
Subject: Re: [Cake] [PATCH net-next v14 6/7] sch_cake: Add overhead
 compensation support to the rate shaper

On Mon, May 21, 2018 at 10:35:58PM +0200, Toke Høiland-Jørgensen wrote:
> +static u32 cake_overhead(struct cake_sched_data *q, const struct sk_buff *skb)
> +{
> +	const struct skb_shared_info *shinfo = skb_shinfo(skb);
> +	unsigned int hdr_len, last_len = 0;
> +	u32 off = skb_network_offset(skb);
> +	u32 len = qdisc_pkt_len(skb);
> +	u16 segs = 1;
> +
> +	q->avg_netoff = cake_ewma(q->avg_netoff, off << 16, 8);
> +
> +	if (!shinfo->gso_size)
> +		return cake_calc_overhead(q, len, off);
> +
> +	/* borrowed from qdisc_pkt_len_init() */
> +	hdr_len = skb_transport_header(skb) - skb_mac_header(skb);
> +
> +	/* + transport layer */
> +	if (likely(shinfo->gso_type & (SKB_GSO_TCPV4 |
> +						SKB_GSO_TCPV6))) {
> +		const struct tcphdr *th;
> +		struct tcphdr _tcphdr;
> +
> +		th = skb_header_pointer(skb, skb_transport_offset(skb),
> +					sizeof(_tcphdr), &_tcphdr);
> +		if (likely(th))
> +			hdr_len += __tcp_hdrlen(th);
> +	} else {

I didn't see some code limiting GSO packets to just TCP or UDP. Is it
safe to assume that this packet is an UDP one, and not SCTP or ESP,
for example?

> +		struct udphdr _udphdr;
> +
> +		if (skb_header_pointer(skb, skb_transport_offset(skb),
> +				       sizeof(_udphdr), &_udphdr))
> +			hdr_len += sizeof(struct udphdr);
> +	}
> +
> +	if (unlikely(shinfo->gso_type & SKB_GSO_DODGY))
> +		segs = DIV_ROUND_UP(skb->len - hdr_len,
> +				    shinfo->gso_size);
> +	else
> +		segs = shinfo->gso_segs;
> +
> +	len = shinfo->gso_size + hdr_len;
> +	last_len = skb->len - shinfo->gso_size * (segs - 1);
> +
> +	return (cake_calc_overhead(q, len, off) * (segs - 1) +
> +		cake_calc_overhead(q, last_len, off));
> +}
> +