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

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Date:   Tue, 22 May 2018 10:44:53 +0200
From:   Toke Høiland-Jørgensen <toke@...e.dk>
To:     Marcelo Ricardo Leitner <marcelo.leitner@...il.com>
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 22 May 2018 01:45:13 CEST, Marcelo Ricardo Leitner <marcelo.leitner@...il.com> wrote:
>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?

As the comment says, I nicked this from the qdisc init code.
So I assume it's safe? :)

>> +		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));
>> +}
>> +