netdev - Re: [RFC] Packet pacing (offload) for flow-aggregates and forwarding use-cases

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Message-ID: <46bb3497-a3cf-84ce-d0b5-855ecedbac15@mellanox.com>
Date:   Thu, 26 Mar 2020 16:42:01 +0200
From:   Yossi Kuperman <yossiku@...lanox.com>
To:     Eric Dumazet <eric.dumazet@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jiri Pirko <jiri@...lanox.com>
Cc:     Rony Efraim <ronye@...lanox.com>
Subject: Re: [RFC] Packet pacing (offload) for flow-aggregates and forwarding
 use-cases


On 24/03/2020 21:26, Eric Dumazet wrote:
>
> On 3/24/20 12:05 PM, Yossi Kuperman wrote:
>> Hello,
>>
>>  
>>
>> We would like to support a forwarding use-case in which flows are classified and paced
>>
>> according to the selected class. For example, a packet arrives at the ingress hook of interface
>>
>> eth0,  performing a sequence of filters and being redirected to interface eth1. Pacing takes
>>
>> place at the egress qdisc of eth1.
>>
>>  
>>
>> FQ queuing discipline is classless and cannot provide such functionality. Each flow is
>>
>> paced independently, and different pacing is only configurable via a socket-option—less
>>
>> suitable for forwarding  use-case.
>>
>>  
>>
>> It is worth noting that although this functionality might be implemented by stacking multiple
>>
>> queuing disciplines, it will be very difficult to offload to hardware.
>>
>>  
>>
>> We propose introducing yet another classful qdisc, where the user can specify in advance the
>>
>> desired classes (i.e. pacing) and provide filters to classify flows accordingly. Similar to other
>>
>> qdiscs, if skb->priority is already set, we can skip the classification; useful for forwarding
>>
>> use-case, as the user can set the priority field in ingress. Works nicely with OVS/TC.
>>
>>  
>>
>> Any thoughts please?
>>
> Why not using HTB for this typical use case ?


As far as I understand HTB is meant for rate-limiting, is the implementation fine-grained enough to support pacing

as well?