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Bug#926967: Don't recommend irqbalance (was: Re: Handling irqbalance in virtual environments)

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On Fri, Apr 12, 2019 at 10:56:29PM +0200, Bastian Blank wrote:
> > On Fri, 2019-04-12 at 10:53 +0200, Bastian Blank wrote:
> > > It turns out we got again problems with irqbalance.
> > > 
> > > It was added as recommends of the main image in 3.16, as it was reported
> > > that older kernels move all interrupts to CPU 0 without help.[1]
> > > 
> > > In the meantime the kernel can do balancing on it's own.  In 4.9, I've
> > > seen it working with aacraid, each queue gets hard pinned to it's own
> > > CPU from 0 to $NRCPUS.  In 4.19 I've seen the same working properly with
> > > virtio-net.
> > > 
> > > With 4.19, even on real hardware, where interrupts have an affinity for
> > > all cpus, each interrupt is actually delivered to different cpu.
> > > 
> > > Random example for this, it even selects only one thread of each core:
> > > 
> > > >  26:    0    0    0    0   92    0    0    0  IR-PCI-MSI 3670017-edge      eno1-TxRx-0
> > > >  27:    0    0    0    0    0  167    0    0  IR-PCI-MSI 3670018-edge      eno1-TxRx-1
> > > >  28:    0    0    0    0    0    0  467    0  IR-PCI-MSI 3670019-edge      eno1-TxRx-2
> > > >  29:    0    0    0    0    0    0    0  454  IR-PCI-MSI 3670020-edge      eno1-TxRx-3
> > > 
> > > Now irqbalance comes to re-do the existing pinning, and the result is not
> > > longer correct but $RANDOM for the hard queue-to-cpu case of virtio.
> > 
> > Then let's drop the recommendation.
> 
> Okay.

+1 !  On what appears to be a related note, irqbalance + linux-4.19
appears to cause a 1.5-to-2.5w power regression on my Thinkpad X220 vs
irqbalance + linux-4.9, even when no VMs are running.

Cheers,
Nicholas

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Bug#926967: Don't recommend irqbalance (was: Re: Handling irqbalance in virtual environments) Bastian Blank <waldi@debian.org> - 2019-04-12 23:10 +0200
  Bug#926967: Don't recommend irqbalance (was: Re: Handling irqbalance in virtual environments) Nicholas D Steeves <nsteeves@gmail.com> - 2019-04-15 01:00 +0200
  Bug#926967: Don't recommend irqbalance (was: Re: Handling irqbalance in virtual environments) Bastian Blank <waldi@debian.org> - 2019-04-23 21:50 +0200

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