netdev - Re: [PATCH net-next 0/5] devlink rate police limiter

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Date:   Fri, 8 Jul 2022 09:27:14 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Jiri Pirko <jiri@...dia.com>, Dima Chumak <dchumak@...dia.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        Simon Horman <horms@...ge.net.au>
Subject: Re: [PATCH net-next 0/5] devlink rate police limiter

Thu, Jul 07, 2022 at 10:16:49PM CEST, kuba@...nel.org wrote:
>On Thu, 7 Jul 2022 13:20:12 +0200 Jiri Pirko wrote:
>> Wait. Lets draw the basic picture of "the wire":
>> 
>> --------------------------+                +--------------------------
>> eswitch representor netdev|=====thewire====|function (vf/sf/whatever
>> --------------------------+                +-------------------------
>> 
>> Now the rate setting Dima is talking about, it is the configuration of
>> the "function" side. Setting the rate is limitting the "function" TX/RX
>> Note that this function could be of any type - netdev, rdma, vdpa, nvme.
>
>The patches add policing, are you saying we're gonna drop RDMA or NVMe
>I/O?

Well, there is some limit to the rate of VF anyway, so at some point,
the packets need to be dropped, with or without policing.
Not really sure how that is handled in rdma and nvme.


>
>> Configuring the TX/RX rate (including groupping) applies to all of
>> these.
>
>I don't understand why the "side of the wire" matters when the patches
>target both Rx and Tx. Surely that covers both directions.

Hmm, I believe it really does. We have objects which we configure. There
is a function object, which has some configuration (including this).
Making user to configure function object via another object (eswitch
port netdevice on the other side of the wire), is quite confusing and I
feel it is wrong. The only reason is to somehow fit TC interface for
which we don't have an anchor for port function.

What about another configuration? would it be ok to use eswitch port
netdev to configure port function too, if there is an interface for it?
I believe not, that is why we introduced port function.


>
>> Putting the configuration on the eswitch representor does not fit:
>> 1) it is configuring the other side of the wire, the configuration
>>    should be of the eswitch port. Configuring the other side is
>>    confusing and misleading. For the purpose of configuring the
>>    "function" side, we introduced "port function" object in devlink.
>> 2) it is confuguring netdev/ethernet however the confuguration applies
>>    to all queues of the function.
>
>If you think it's technically superior to put it in devlink that's fine.
>I'll repeat myself - what I'm asking for is convergence so that drivers
>don't have  to implement 3 different ways of configuring this. We have
>devlink rate for from-VF direction shaping, tc police for bi-dir
>policing and obviously legacy NDOs. None of them translate between each
>other so drivers and user space have to juggle interfaces.

The legacy ndo is legacy. Drivers that implement switchdev mode do
not implement those, and should not.