netdev - Re: [net-next/RFC PATCH v1 1/4] net: Introduce new napi fields for rx/tx queues

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Date: Tue, 1 Aug 2023 18:26:26 -0600
From: David Ahern <dsahern@...nel.org>
To: Jakub Kicinski <kuba@...nel.org>,
 "Nambiar, Amritha" <amritha.nambiar@...el.com>
Cc: netdev@...r.kernel.org, davem@...emloft.net, sridhar.samudrala@...el.com
Subject: Re: [net-next/RFC PATCH v1 1/4] net: Introduce new napi fields for
 rx/tx queues

On 7/28/23 5:09 PM, Jakub Kicinski wrote:
> On Fri, 28 Jul 2023 15:37:14 -0700 Nambiar, Amritha wrote:
>> Hi Jakub, I have the next version of patches ready (I'll send that in a 
>> bit). I suggest if you could take a look at it and let me know your 
>> thoughts and then we can proceed from there.
> 
> Great, looking forward.
> 
>> About dumping queues and NAPIs separately, are you thinking about having 
>> both per-NAPI and per-queue instances, or do you think only one will 
>> suffice. The plan was to follow this work with a 'set-napi' series, 
>> something like,
>> set-napi <napi_id> queues <q_id1, q_id2, ...>
>> to configure the queue[s] that are to be serviced by the napi instance.
>>
>> In this case, dumping the NAPIs would be beneficial especially when 
>> there are multiple queues on the NAPI.
>>
>> WRT per-queue, are there a set of parameters that needs to exposed 
>> besides what's already handled by ethtool...
> 
> Not much at this point, maybe memory model. Maybe stats if we want to
> put stats in the same command. But the fact that sysfs has a bunch of
> per queue attributes makes me think that sooner or later we'll want
> queue as a full object in netlink. And starting out that way makes 
> the whole API cleaner, at least in my opinion.
> 
> If we have another object which wants to refer to queues (e.g. page
> pool) it's easier to express the topology when it's clear what is an
> object and what's just an attribute.
> 
>> Also, to configure a queue 
>> on a NAPI, set-queue <qid> <napi_id>, the existing NAPIs would have to 
>> be looked up from the queue parameters dumped.
> 
> The look up should not be much of a problem.
> 
> And don't you think that:
> 
>   set-queue queue 1 napi-id 101
>   set-queue queue 2 napi-id 101
> 
> is more natural than:
> 
>   set-napi napi-id 101 queues [1, 2]
> 
> Especially in presence of conflicts. If user tries:
> 
>   set-napi napi-id 101 queues [1, 2]
>   set-napi napi-id 102 queues [1, 2]
> 
> Do both napis now serve those queues? May seem obvious to us, but
> "philosophically" why does setting an attribute of object 102 change
> attributes of object 101?
> 
> If we ever gain the ability to create queues it will be:
> 
>   create-queue napi-id xyz
> 
> which also matches set-queue more nicely than napi base API.
> 

I take it you have this path in mind as a means of creating
"specialized" queues (e.g., io_uring and Rx ZC). Any slides or notes on
the bigger picture?