[Cake] Fwd: Re: Unable to create htb tc classes more than 64K

[Cake] Fwd: Re: Unable to create htb tc classes more than 64K

[Toke Høiland-Jørgensen]

[-- Attachment #1: Type: text/plain, Size: 214 bytes --]

Turns out that with the "earliest departure time" support in sched_fq,
it is now possible to write a shaper in eBPF, thus avoiding the global
qdisc lock in sched_htb. This is pretty cool, if you ask me! :)

-Toke


[-- Attachment #2: Type: message/rfc822, Size: 11786 bytes --]

From: Eric Dumazet <eric.dumazet@gmail.com>
To: Cong Wang <xiyou.wangcong@gmail.com>, Akshat Kakkar <akshat.1984@gmail.com>
Cc: Anton Danilov <littlesmilingcloud@gmail.com>, NetFilter <netfilter-devel@vger.kernel.org>, lartc <lartc@vger.kernel.org>, netdev <netdev@vger.kernel.org>
Subject: Re: Unable to create htb tc classes more than 64K
Date: Mon, 26 Aug 2019 08:32:48 +0200
Message-ID: <9cbefe10-b172-ae2a-0ac7-d972468eb7a2@gmail.com>



On 8/25/19 7:52 PM, Cong Wang wrote:
> On Wed, Aug 21, 2019 at 11:00 PM Akshat Kakkar <akshat.1984@gmail.com> wrote:
>>
>> On Thu, Aug 22, 2019 at 3:37 AM Cong Wang <xiyou.wangcong@gmail.com> wrote:
>>>> I am using ipset +  iptables to classify and not filters. Besides, if
>>>> tc is allowing me to define qdisc -> classes -> qdsic -> classes
>>>> (1,2,3 ...) sort of structure (ie like the one shown in ascii tree)
>>>> then how can those lowest child classes be actually used or consumed?
>>>
>>> Just install tc filters on the lower level too.
>>
>> If I understand correctly, you are saying,
>> instead of :
>> tc filter add dev eno2 parent 100: protocol ip prio 1 handle
>> 0x00000001 fw flowid 1:10
>> tc filter add dev eno2 parent 100: protocol ip prio 1 handle
>> 0x00000002 fw flowid 1:20
>> tc filter add dev eno2 parent 100: protocol ip prio 1 handle
>> 0x00000003 fw flowid 2:10
>> tc filter add dev eno2 parent 100: protocol ip prio 1 handle
>> 0x00000004 fw flowid 2:20
>>
>>
>> I should do this: (i.e. changing parent to just immediate qdisc)
>> tc filter add dev eno2 parent 1: protocol ip prio 1 handle 0x00000001
>> fw flowid 1:10
>> tc filter add dev eno2 parent 1: protocol ip prio 1 handle 0x00000002
>> fw flowid 1:20
>> tc filter add dev eno2 parent 2: protocol ip prio 1 handle 0x00000003
>> fw flowid 2:10
>> tc filter add dev eno2 parent 2: protocol ip prio 1 handle 0x00000004
>> fw flowid 2:20
> 
> 
> Yes, this is what I meant.
> 
> 
>>
>> I tried this previously. But there is not change in the result.
>> Behaviour is exactly same, i.e. I am still getting 100Mbps and not
>> 100kbps or 300kbps
>>
>> Besides, as I mentioned previously I am using ipset + skbprio and not
>> filters stuff. Filters I used just to test.
>>
>> ipset  -N foo hash:ip,mark skbinfo
>>
>> ipset -A foo 10.10.10.10, 0x0x00000001 skbprio 1:10
>> ipset -A foo 10.10.10.20, 0x0x00000002 skbprio 1:20
>> ipset -A foo 10.10.10.30, 0x0x00000003 skbprio 2:10
>> ipset -A foo 10.10.10.40, 0x0x00000004 skbprio 2:20
>>
>> iptables -A POSTROUTING -j SET --map-set foo dst,dst --map-prio
> 
> Hmm..
> 
> I am not familiar with ipset, but it seems to save the skbprio into
> skb->priority, so it doesn't need TC filter to classify it again.
> 
> I guess your packets might go to the direct queue of HTB, which
> bypasses the token bucket. Can you dump the stats and check?

With more than 64K 'classes' I suggest to use a single FQ qdisc [1], and
an eBPF program using EDT model (Earliest Departure Time)

The BPF program would perform the classification, then find a data structure
based on the 'class', and then update/maintain class virtual times and skb->tstamp

TBF = bpf_map_lookup_elem(&map, &classid);

uint64_t now = bpf_ktime_get_ns();
uint64_t time_to_send = max(TBF->time_to_send, now);

time_to_send += (u64)qdisc_pkt_len(skb) * NSEC_PER_SEC / TBF->rate;
if (time_to_send > TBF->max_horizon) {
    return TC_ACT_SHOT;
}
TBF->time_to_send = time_to_send;
skb->tstamp = max(time_to_send, skb->tstamp);
if (time_to_send - now > TBF->ecn_horizon)
    bpf_skb_ecn_set_ce(skb);
return TC_ACT_OK;

tools/testing/selftests/bpf/progs/test_tc_edt.c shows something similar.


[1]  MQ + FQ if the device is multi-queues.

   Note that this setup scales very well on SMP, since we no longer are forced
 to use a single HTB hierarchy (protected by a single spinlock)

Re: [Cake] Fwd: Re: Unable to create htb tc classes more than 64K

[Stephen Hemminger]

On Mon, 26 Aug 2019 09:35:14 +0200
Toke Høiland-Jørgensen <toke@redhat.com> wrote:

> Turns out that with the "earliest departure time" support in sched_fq,
> it is now possible to write a shaper in eBPF, thus avoiding the global
> qdisc lock in sched_htb. This is pretty cool, if you ask me! :)
> 
> -Toke
> 

Thanks, I may use this to revisit doing netem in eBPF (xnetem).
Not having this feature was a show stopper at the time.