Re: This is the fourth time I’ve tried to find what led to the regression of outgoing network speed and each time I find the merge commit 8c94ccc7cd691472461448f98e2372c75849406c

[Mathias Nyman]

On 21.2.2024 1.43, Randy Dunlap wrote:
> On 2/20/24 15:41, Randy Dunlap wrote:
> > {+ tglx]
>
> (this time for real)
>
> > On 2/20/24 15:19, Mikhail Gavrilov wrote:
> > > On Mon, Feb 19, 2024 at 2:41 PM Mikhail Gavrilov
> > > <mikhail.v.gavrilov@xxxxxxxxx> wrote:
> > > > I installed irqbalance daemon and nothing changed.
> > > > So who is responsible for irq balancing?
> > >
> > > Sorry for the noise. Can anyone give me an answer?
> > > Who is responsible for distributing interrupts in Linux?
> > > I spotted network performance regression and it turned out, this was
> > > due to the network card getting other interrupt. It is a side effect
> > > of commit 57e153dfd0e7a080373fe5853c5609443d97fa5a.
> >
> > That's a merge commit (AFAIK, maybe not so much). The commit in mainline is:
> >
> > commit f977f4c9301c
> > Author: Niklas Neronin <niklas.neronin@xxxxxxxxxxxxxxx>
> > Date:   Fri Dec 1 17:06:40 2023 +0200
> >
> >      xhci: add handler for only one interrupt line
> >
> > > Installing irqbalance daemon did not help. Maybe someone experienced
> > > such a problem?
> >
> > Thomas, would you look at this, please?
> >
> > A network device and xhci (USB) driver are now sharing interrupts.
> > This causes a large performance decrease for the networking device.

Short recap:

xhci (USB) and network device didn't share interrupts, or even interrupt the
same CPU in either good or bad case.

A change in how many interrupts xhci driver requests changed which CPU
the network device interrupts.

In the bad case Mikhail Gavrilovs network device was interrupting CPU0
together with:
- IR-IO-APIC    2-edge      timer
- IR-PCI-MSIX-0000:07:00.0    1-edge      nvme1q1

In the good case network device was interrupting CPU27 together with:
- IR-PCI-MSIX-0000:04:00.0   27-edge      nvme0q27
- IR-PCI-MSIX-0000:07:00.0   28-edge      nvme1q28

Manually moving network device irq 87 from CPU0 to CPU23 helped.
(echo 800000 > /proc/irq/87/smp_affinity)

Thanks
-Mathias