Re: [PATCH v2] block: fix rdma queue mapping

Shiraz Saleem
2018-10-24T00:09:23Z

On Tue, Oct 23, 2018 at 03:25:06PM -0600, Sagi Grimberg wrote:
>
> >>>> Christoph, Sagi: it seems you think /proc/irq/$IRP/smp_affinity
> >>>> shouldn't be allowed if drivers support managed affinity. Is that correct?
> >>>
> >>> Not just shouldn't, but simply can't.
> >>>
> >>>> But as it stands, things are just plain borked if an rdma driver
> >>>> supports ib_get_vector_affinity() yet the admin changes the affinity via
> >>>> /proc...
> >>>
> >>> I think we need to fix ib_get_vector_affinity to not return anything
> >>> if the device doesn't use managed irq affinity.
> >>
> >> Steve, does iw_cxgb4 use managed affinity?
> >>
> >> I'll send a patch for mlx5 to simply not return anything as managed
> >> affinity is not something that the maintainers want to do.
> >
> > I'm beginning to think I don't know what "managed affinity" actually is. Currently iw_cxgb4 doesn't support ib_get_vector_affinity(). I have a patch for it, but ran into this whole issue with nvme failing if someone changes the affinity map via /proc.
>
> That means that the pci subsystem gets your vector(s) affinity right and
> immutable. It also guarantees that you have reserved vectors and not get
> a best effort assignment when cpu cores are offlined.
>
> You can simply enable it by adding PCI_IRQ_AFFINITY to
> pci_alloc_irq_vectors() or call pci_alloc_irq_vectors_affinity()
> to communicate post/pre vectors that don't participate in
> affinitization (nvme uses it for admin queue).
>
> This way you can easily plug ->get_vector_affinity() to return
> pci_irq_get_affinity(dev, vector)
>
> The original patch set from hch:
> https://lwn.net/Articles/693653/

Sagi - From what I can tell, i40iw is also exposed to this same issue if the IRQ affinity
is configured by user.

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