linux-kernel - Re: [Intel-wired-lan] [iwl-net PATCH v2] idpf: change IRQ naming to match netdev and ethtool queue numbering

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Message-ID: <649ae4be-3081-49a2-8ac7-18724272498f@lunn.ch>
Date: Mon, 26 Jan 2026 22:12:31 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Eric Dumazet <edumazet@...gle.com>
Cc: Jacob Keller <jacob.e.keller@...el.com>,
	Brian Vazquez <brianvv@...gle.com>,
	Brian Vazquez <brianvv.kernel@...il.com>,
	Tony Nguyen <anthony.l.nguyen@...el.com>,
	Przemek Kitszel <przemyslaw.kitszel@...el.com>,
	"David S. Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	intel-wired-lan@...ts.osuosl.org,
	David Decotigny <decot@...gle.com>, Li Li <boolli@...gle.com>,
	Anjali Singhai <anjali.singhai@...el.com>,
	Sridhar Samudrala <sridhar.samudrala@...el.com>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	emil.s.tantilov@...el.com, Brett Creeley <brett.creeley@....com>,
	Aleksandr Loktionov <aleksandr.loktionov@...el.com>
Subject: Re: [Intel-wired-lan] [iwl-net PATCH v2] idpf: change IRQ naming to
 match netdev and ethtool queue numbering

On Mon, Jan 26, 2026 at 09:51:10PM +0100, Eric Dumazet wrote:
> On Mon, Jan 26, 2026 at 9:46 PM Jacob Keller <jacob.e.keller@...el.com> wrote:
> >
> >
> >
> > On 1/26/2026 9:53 AM, Andrew Lunn wrote:
> > > On Mon, Jan 26, 2026 at 12:40:15PM -0500, Brian Vazquez wrote:
> > >> On Mon, Jan 26, 2026 at 11:24 AM Andrew Lunn <andrew@...n.ch> wrote:
> > >>>
> > >>> On Mon, Jan 26, 2026 at 02:46:24PM +0000, Brian Vazquez wrote:
> > >>>> The code uses the vidx for the IRQ name but that doesn't match ethtool
> > >>>> reporting or netdev naming, this makes it hard to tune the device and
> > >>>> associate queues with IRQs. Sequentially requesting irqs starting from
> > >>>> '0' makes the output consistent.
> > >>>>
> > >>>> Before:
> > >>>>
> > >>>> ethtool -L eth1 tx 1 combined 3
> > >>>>
> > >>>> grep . /proc/irq/*/*idpf*/../smp_affinity_list
> > >>>> /proc/irq/67/idpf-Mailbox-0/../smp_affinity_list:0-55,112-167
> > >>>> /proc/irq/68/idpf-eth1-TxRx-1/../smp_affinity_list:0
> > >>>> /proc/irq/70/idpf-eth1-TxRx-3/../smp_affinity_list:1
> > >>>> /proc/irq/71/idpf-eth1-TxRx-4/../smp_affinity_list:2
> > >>>> /proc/irq/72/idpf-eth1-Tx-5/../smp_affinity_list:3
> > >>>>
> > >>>> ethtool -S eth1 | grep -v ': 0'
> > >>>> NIC statistics:
> > >>>>       tx_q-0_pkts: 1002
> > >>>>       tx_q-1_pkts: 2679
> > >>>>       tx_q-2_pkts: 1113
> > >>>>       tx_q-3_pkts: 1192 <----- tx_q-3 vs idpf-eth1-Tx-5
> > >>>>       rx_q-0_pkts: 1143
> > >>>>       rx_q-1_pkts: 3172
> > >>>>       rx_q-2_pkts: 1074
> > >>>>
> > >>>> After:
> > >>>>
> > >>>> ethtool -L eth1 tx 1 combined 3
> > >>>>
> > >>>> grep . /proc/irq/*/*idpf*/../smp_affinity_list
> > >>>>
> > >>>> /proc/irq/67/idpf-Mailbox-0/../smp_affinity_list:0-55,112-167
> > >>>> /proc/irq/68/idpf-eth1-TxRx-0/../smp_affinity_list:0
> > >>>> /proc/irq/70/idpf-eth1-TxRx-1/../smp_affinity_list:1
> > >>>> /proc/irq/71/idpf-eth1-TxRx-2/../smp_affinity_list:2
> > >>>> /proc/irq/72/idpf-eth1-Tx-3/../smp_affinity_list:3
> > >>>>
> > >>>> ethtool -S eth1 | grep -v ': 0'
> > >>>> NIC statistics:
> > >>>>       tx_q-0_pkts: 118
> > >>>>       tx_q-1_pkts: 134
> > >>>>       tx_q-2_pkts: 228
> > >>>>       tx_q-3_pkts: 138 <--- tx_q-3 matches idpf-eth1-Tx-3
> > >>>>       rx_q-0_pkts: 111
> > >>>>       rx_q-1_pkts: 366
> > >>>>       rx_q-2_pkts: 120
> > >>>
> > >>> Are there any ABI issues here?
> > >>
> > >> The patch doesn't change the format, it just fixes the numbering in
> > >> the name to make it consistent with other reporting tools. It
> > >> shouldn't break any library.
> > >
> > > But is the numbering part of the ABI?
> > >
> > > Making a comment about ABI in the commit message makes it clear it is
> > > something you have considered, and you have decided it is not an
> > > issue. If there is no such comment, reviewers probably should ask.
> > >
> > >         Andrew
> >
> > I don't see how an application can depend on the name if it can't
> > correlate it to anything meaningful. The change fixes the ID values used
> > so that they *do* correlate. If an application was previously assuming
> > it correlated to the queue ID, it would incorrect associate the IRQ with
> > the wrong queue.
> 
> Agree, this mismatch caused me some surprises, we can not keep a broken
> ABI (which has been broken by accident)

So everybody is agreed, great. I just think it would of been good to
mention ABI in the commit message, to show due diligence has been
done.

   Andrew