netdev - Re: [PATCH net-next 5/7] igc: add private flag to reverse TX queue priority in TSN mode

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Message-ID: <61c54e7b-9ffd-45c4-b37f-c570e310ea45@redhat.com>
Date: Tue, 17 Jun 2025 14:45:50 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Vladimir Oltean <vladimir.oltean@....com>,
 Tony Nguyen <anthony.l.nguyen@...el.com>,
 Faizal Rahim <faizal.abdul.rahim@...ux.intel.com>
Cc: faizal.abdul.rahim@...el.com, chwee.lin.choong@...el.com,
 horms@...nel.org, vitaly.lifshits@...el.com, dima.ruinskiy@...el.com,
 Mor Bar-Gabay <morx.bar.gabay@...el.com>, davem@...emloft.net,
 edumazet@...gle.com, andrew+netdev@...n.ch, netdev@...r.kernel.org,
 kuba@...nel.org
Subject: Re: [PATCH net-next 5/7] igc: add private flag to reverse TX queue
 priority in TSN mode

On 6/17/25 2:17 PM, Vladimir Oltean wrote:
> On Tue, Jun 17, 2025 at 12:06:14PM +0200, Paolo Abeni wrote:
>> On 6/11/25 8:03 PM, Tony Nguyen wrote:
>>> To harmonize TX queue priority behavior between taprio and mqprio, and
>>> to fix these issues without breaking long-standing taprio use cases,
>>> this patch adds a new private flag, called reverse-tsn-txq-prio, to
>>> reverse the TX queue priority. It makes queue 3 the highest and queue 0
>>> the lowest, reusing the TX arbitration logic already used by mqprio.
>> Isn't the above quite the opposite of what Vladimir asked in
>> https://lore.kernel.org/all/20250214113815.37ttoor3isrt34dg@skbuf/ ?
>>
>> """
>> I would expect that for uniform behavior, you would force the users a
>> little bit to adopt the new TX scheduling mode in taprio, otherwise any
>> configuration with preemptible traffic classes would be rejected by the
>> driver.
>> """
>>
>> I don't see him commenting on later version, @Vladimir: does this fits you?
> 
> Indeed, sorry for disappearing from the patch review process.
> 
> I don't see the discrepancy between what Faizal implemented and what we
> discussed. Specifically on the bit you quoted - patch "igc: add
> preemptible queue support in taprio" refuses taprio schedules with
> preemptible TCs if the user hasn't explicitly opted into
> IGC_FLAG_TSN_REVERSE_TXQ_PRIO. If that private flag isn't set,
> everything works as currently documented, just the new features are
> gated.
> 
> The name of the private flag is debatable IMHO, because it's taprio
> specific and the name doesn't reflect that (mqprio uses the "reverse"
> priority assignment to TX queues by default, and this flag doesn't
> change that). Also, "reverse" compared to what? Both operating modes can
> equally be named "reverse". Maybe "taprio-standard-txq-priority" would
> have been clearer regarding what the flag really does. Anyway, I don't
> want to stir up a huge debate around naming if functionality-wise it's
> the same thing, they have to maintain it, I don't.
> 
> Is there something I'm missing? It feels like it.

I misread your original comment as a request to make the 'standard'
priority the default, and the current one reachable only enabling the
priv flag.

I see you are fine with the current status, so the answer to your
question is 'no' ;)

Paolo