netdev - Re: [RFC PATCH net-next v1 1/2] net: add name field to napi struct

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Message-ID: <2ce5ff9d-7453-f48e-7e84-539752f72be5@oss.nxp.com>
Date:   Tue, 11 May 2021 18:44:26 +0200
From:   Yannick Vignon <yannick.vignon@....nxp.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Antoine Tenart <atenart@...nel.org>,
        Wei Wang <weiwan@...gle.com>, Taehee Yoo <ap420073@...il.com>,
        Alexander Lobakin <alobakin@...me>,
        netdev <netdev@...r.kernel.org>,
        Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Jose Abreu <joabreu@...opsys.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Joakim Zhang <qiangqing.zhang@....com>,
        sebastien.laveze@....nxp.com,
        Yannick Vignon <yannick.vignon@....com>
Subject: Re: [RFC PATCH net-next v1 1/2] net: add name field to napi struct

On 5/6/2021 7:35 PM, Eric Dumazet wrote:
> On Thu, May 6, 2021 at 7:20 PM Yannick Vignon
> <yannick.vignon@....nxp.com> wrote:
>>
>> From: Yannick Vignon <yannick.vignon@....com>
>>
>> An interesting possibility offered by the new thread NAPI code is to
>> fine-tune the affinities and priorities of different NAPI instances. In a
>> real-time networking context, this makes it possible to ensure packets
>> received in a high-priority queue are always processed, and with low
>> latency.
>>
>> However, the way the NAPI threads are named does not really expose which
>> one is responsible for a given queue. Assigning a more explicit name to
>> NAPI instances can make that determination much easier.
>>
>> Signed-off-by: Yannick Vignon <yannick.vignon@....com>
>> -
> 
> Having to change drivers seems a lot of work
> 
> How about exposing thread id (and napi_id eventually) in
> /sys/class/net/eth0/queues/*/kthread_pid  ?
> 

This seemed like a good idea, but after looking into how to actually 
implement it, I can't find a way to "map" rx queues to napi instances. 
Am I missing something?

In the end, I'm afraid that the NAPI<->RX queue mapping is only known 
within the drivers, so we'll have no choice but to modify them
to extract that information somehow.