Re: [Cake] Using cake to shape 1000’s of users.

[Dave Taht <dave.taht@gmail.com>]

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On Sat, Jul 28, 2018 at 10:38 AM Pete Heist <pete@heistp.net> wrote:
>
>
> On Jul 28, 2018, at 10:56 AM, Toke Høiland-Jørgensen <toke@toke.dk> wrote:
>
> Note that with the existing tc classifier stuff we already added to
> Cake, we basically have this already (eBPF can map traffic to tin and
> flow however it pleases).
>
>
> Sorry, this just jostled in my brain now that I may be able to implement member fairness today, based on what you wrote earlier in a thread that I entirely missed: https://lists.bufferbloat.net/pipermail/cake/2018-May/003811.html
>
> George posted an example of assigning packets to a tin: https://lists.bufferbloat.net/pipermail/cake/2018-May/003809.html
>
> How does one send packets to a specific flow / queue?

It's essentially above. I think you can actually do it in pure bpf
without skbedit, I'd written a tc bpf flow classifier for acks quite
some time ago. The not current version is attached. I really need to
finish up some ack related stuff.
Using a bpf map to this then setting the flowid directly?


> This wouldn’t give both per-member and per-flow fairness, but at least per-member fairness might be possible. There are 1024(?) queues available and 800 members, so I’m just speculating that I could map members to a number from 0 to 800 (active member IDs packed and zero-based would work) and assign each member to their own flow. Thanks... :)
>
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--

Dave Täht
CEO, TekLibre, LLC
http://www.teklibre.com
Tel: 1-669-226-2619

[-- Attachment #2: ack_recognise.c --]
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/* ack_recogniser: An eBPF program that correctly recognises modern TCP ACKs,
   with tcp option fields.
 */

#include "bpf_api.h"
#include "uapi/linux/if_ether.h"
#include "uapi/linux/ip.h"
#include "uapi/linux/in.h"
// #include "uapi/linux/ipv6.h" // iproute2 doesn't import this header
#include "uapi/linux/tcp.h"

/* Idealized syntax example to move acks into a priority queue:

tc qdisc del dev $IFACE root 2> /dev/null
tc qdisc add dev $IFACE root handle 1: prio bands 3 priomap 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
tc qdisc add dev $IFACE parent 1:1 handle 10:1 fq_codel
tc qdisc add dev $IFACE parent 1:2 handle 20:1 fq_codel
tc qdisc add dev $IFACE parent 1:3 handle 30:1 fq_codel

tc filter add dev $IFACE  prio 1 bpf object-file ack_recognise.o da ack_match flowid 10:1 # 1:1?

*/

/* A pure ack contains the ip header, the tcp header + options, flags with the
 * ack field set, and no additional payload. That last bit is what every prior
 * ack filter gets wrong, they typically assume an obsolete 64 bytes.
 */

__section_cls_entry
int ack_match(struct __sk_buff *skb)
{
	void *data = (void *)(long)skb->data;
	void *data_end = (void *)(long)skb->data_end;
	struct ethhdr *eth = data;
	struct iphdr *iph = data + sizeof(*eth);
	struct tcphdr *tcp;
	int len, isize;

	if (data + sizeof(*eth) + sizeof(*iph) + sizeof(*tcp) > data_end)
		return 0;

	if (eth->h_proto != htons(ETH_P_IP))
		return 0;

	if (iph->version == 4) {
		if(iph->protocol != IPPROTO_TCP)
			return 0;
		len = iph->tot_len; // htons?
		if(iph->ihl > 4) {
			isize = (iph->ihl+1) * 4 - sizeof(*iph);
			tcp = data + sizeof(*eth) + isize;
		} else {
			return 0;
		}
/* grump: iproute2 does not export ip6hdrs
	} else  if (iph->version == 6) {
		struct ipv6hdr iph6 = (struct ipv6hdr *) iph;
// FIXME: walk ip6hdrs appropriately
		if(iph6->nexthdr != IPPROTO_TCP)
			return 0;
		len = iph6->payload_len;
		isize = sizeof(*iph6) + ??;
		tcp = data + sizeof(*eth) + isize;
		*/
	} else
		return 0;

	if (!tcp->ack) return 0;

	if (isize + sizeof(*tcp) + tcp->doff*4 == len)
		return -1; // We matched, return TC_ACT_RECLASSIFY?

	return 0;
}

char __license[] __section("license") = "GPL";