IRQ assignment for queues

IRQ assignment for queues

[Srivats P]

Hi,

Not a XDP question, but more generic about IRQ assignment for queues.

For a NIC which has separate RX and TX queues (no COMBINED queues), I
see in /proc/interrupts that only 1 IRQ is assigned.

srivatsp@EXA8:~$ sudo ethtool -L enp5s0f1 rx 1 tx 1 combined 0
combined unmodified, ignoring
srivatsp@EXA8:~$ ethtool -l enp5s0f1
Channel parameters for enp5s0f1:
Pre-set maximums:
RX:             4
TX:             4
Other:          0
Combined:       0
Current hardware settings:
RX:             1
TX:             1
Other:          0
Combined:       0

srivatsp@EXA8:~$ cat /proc/interrupts | grep enp5s0f1
 73:          0          2          0          0   ITS-MSI 2623488
Edge      enp5s0f1-rxtx-0
 89:          0          0          0          0   ITS-MSI 2623504
Edge      enp5s0f1-rbdr-0
 92:          0          0          0          0   ITS-MSI 2623507
Edge      enp5s0f1-qset-err-0

Is the IRQ for the RX queue or TX queue or both? Does Tx need an IRQ?

Srivats

Re: IRQ assignment for queues

[Zvi Effron]

On Tue, Apr 20, 2021 at 11:57 PM Srivats P <pstavirs@gmail.com> wrote:
>
> Hi,
>
> Not a XDP question, but more generic about IRQ assignment for queues.
>
> For a NIC which has separate RX and TX queues (no COMBINED queues), I
> see in /proc/interrupts that only 1 IRQ is assigned.
>
> ...
>
> srivatsp@EXA8:~$ cat /proc/interrupts | grep enp5s0f1
>  73:          0          2          0          0   ITS-MSI 2623488
> Edge      enp5s0f1-rxtx-0
>  89:          0          0          0          0   ITS-MSI 2623504
> Edge      enp5s0f1-rbdr-0
>  92:          0          0          0          0   ITS-MSI 2623507
> Edge      enp5s0f1-qset-err-0
>
> Is the IRQ for the RX queue or TX queue or both? Does Tx need an IRQ?

I see the IRQ name has "rxtx" in it. From my experience, that's the
same type of designation used for combined queues, and indicates that
the IRQ is for both RX and TX. I'm not sure which driver you're using,
though, and my experience is mostly with i40e and ena drivers, so it
could be incorrect when applied to your case.

--Zvi

Re: IRQ assignment for queues

[Srivats P]

On Thu, Apr 22, 2021 at 3:14 AM Zvi Effron <zeffron@riotgames.com> wrote:
>
> On Tue, Apr 20, 2021 at 11:57 PM Srivats P <pstavirs@gmail.com> wrote:
> >
> > Hi,
> >
> > Not a XDP question, but more generic about IRQ assignment for queues.
> >
> > For a NIC which has separate RX and TX queues (no COMBINED queues), I
> > see in /proc/interrupts that only 1 IRQ is assigned.
> >
> > ...
> >
> > srivatsp@EXA8:~$ cat /proc/interrupts | grep enp5s0f1
> >  73:          0          2          0          0   ITS-MSI 2623488
> > Edge      enp5s0f1-rxtx-0
> >  89:          0          0          0          0   ITS-MSI 2623504
> > Edge      enp5s0f1-rbdr-0
> >  92:          0          0          0          0   ITS-MSI 2623507
> > Edge      enp5s0f1-qset-err-0
> >
> > Is the IRQ for the RX queue or TX queue or both? Does Tx need an IRQ?
>
> I see the IRQ name has "rxtx" in it. From my experience, that's the
> same type of designation used for combined queues, and indicates that
> the IRQ is for both RX and TX.

I guessed as much (based on i40e combined TxRx queues experience), but
wanted to confirm.

> I'm not sure which driver you're using,

This output and query was for the Cavium ThunderX nic_vf driver specifically.

> though, and my experience is mostly with i40e and ena drivers, so it
> could be incorrect when applied to your case.
>
> --Zvi