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From: "Toke Høiland-Jørgensen" <toke@toke.dk>
To: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Cc: netdev@vger.kernel.org, cake@lists.bufferbloat.net
Subject: Re: [Cake] [PATCH net-next v14 6/7] sch_cake: Add overhead compensation support to the rate shaper
Date: Wed, 23 May 2018 00:06:42 +0200	[thread overview]
Message-ID: <87lgcbxs3x.fsf@toke.dk> (raw)
In-Reply-To: <20180522202241.GJ5488@localhost.localdomain>

Marcelo Ricardo Leitner <marcelo.leitner@gmail.com> writes:

> On Tue, May 22, 2018 at 10:44:53AM +0200, Toke Høiland-Jørgensen wrote:
>> 
>> 
>> On 22 May 2018 01:45:13 CEST, Marcelo Ricardo Leitner <marcelo.leitner@gmail.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? :)
>
> As long as it doesn't go further than this, it is. As in, it is just
> validating if it can contain an UDP header, and if so, account for its
> size, without actually reading the header.
>
> Considering everything !TCP as UDP work as an approximation, which is
> quite accurate. SCTP header is just 4 bytes bigger than UDP header and
> is equal to ESP header size.

Yup, that seems close enough for our purposes. Thanks for explaining.
Didn't actually know that GSO handles other protocols as well :)

-Toke

  reply	other threads:[~2018-05-22 22:06 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-21 20:35 [Cake] [PATCH net-next v14 0/7] sched: Add Common Applications Kept Enhanced (cake) qdisc Toke Høiland-Jørgensen
2018-05-21 20:35 ` [Cake] [PATCH net-next v14 7/7] sch_cake: Conditionally split GSO segments Toke Høiland-Jørgensen
2018-05-21 20:35 ` [Cake] [PATCH net-next v14 5/7] sch_cake: Add DiffServ handling Toke Høiland-Jørgensen
2018-05-21 20:35 ` [Cake] [PATCH net-next v14 1/7] sched: Add Common Applications Kept Enhanced (cake) qdisc Toke Høiland-Jørgensen
2018-05-21 20:35 ` [Cake] [PATCH net-next v14 6/7] sch_cake: Add overhead compensation support to the rate shaper Toke Høiland-Jørgensen
2018-05-21 23:45   ` Marcelo Ricardo Leitner
2018-05-22  8:44     ` Toke Høiland-Jørgensen
2018-05-22 20:22       ` Marcelo Ricardo Leitner
2018-05-22 22:06         ` Toke Høiland-Jørgensen [this message]
2018-05-21 20:35 ` [Cake] [PATCH net-next v14 4/7] sch_cake: Add NAT awareness to packet classifier Toke Høiland-Jørgensen
2018-05-21 23:34   ` Marcelo Ricardo Leitner
2018-05-22  8:45     ` Toke Høiland-Jørgensen
2018-05-21 20:35 ` [Cake] [PATCH net-next v14 3/7] sch_cake: Add optional ACK filter Toke Høiland-Jørgensen
2018-05-21 21:15   ` Eric Dumazet
2018-05-21 20:35 ` [Cake] [PATCH net-next v14 2/7] sch_cake: Add ingress mode Toke Høiland-Jørgensen

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