Re: Handling irqbalance in virtual environments

From	Ben Hutchings <ben@decadent.org.uk>
Newsgroups	linux.debian.kernel
Subject	Re: Handling irqbalance in virtual environments
Date	2019-04-12 22:20 +0200
Message-ID	<xMaOt-ce-5@gated-at.bofh.it> (permalink)
References	<xM0m6-2fa-5@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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On Fri, 2019-04-12 at 10:53 +0200, Bastian Blank wrote:
> Moin
> 
> 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.

Ben.

> At least Google considers the work irqbalance does to "correct" the existing
> balancing a large problem.
> 
> I'm not sure how to go forward.  I have a workaround pending for our
> cloud images to hard exclude the installation of irqbalance.[2]
> 
> Regards,
> Bastian
> 
> [1]: https://bugs.debian.org/577788
> [2]: https://salsa.debian.org/cloud-team/debian-cloud-images/merge_requests/81
-- 
Ben Hutchings
Hoare's Law of Large Problems:
   Inside every large problem is a small problem struggling to get out.

Thread

Handling irqbalance in virtual environments Bastian Blank <waldi@debian.org> - 2019-04-12 11:10 +0200
  Re: Handling irqbalance in virtual environments Bastian Blank <waldi@debian.org> - 2019-04-12 11:40 +0200
  Re: Handling irqbalance in virtual environments Ben Hutchings <ben@decadent.org.uk> - 2019-04-12 22:20 +0200
    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
      Processed: Re: Bug#926967: Don't recommend irqbalance (was: Re:  Handling irqbalance in virtual environments) "Debian Bug Tracking System" <owner@bugs.debian.org> - 2019-04-23 21:50 +0200

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