linux-kernel - Re: [PATCH v3 2/2] powerpc/pseries: pass MSI affinity to irq_create

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Date:   Thu, 26 Nov 2020 14:22:24 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Marc Zyngier <maz@...nel.org>, Laurent Vivier <lvivier@...hat.com>
Cc:     Denis Kirjanov <kda@...ux-powerpc.org>,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        Christoph Hellwig <hch@....de>,
        Paul Mackerras <paulus@...ba.org>, Greg Kurz <groug@...d.org>,
        linuxppc-dev@...ts.ozlabs.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        linux-block@...r.kernel.org, "Michael S . Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH v3 2/2] powerpc/pseries: pass MSI affinity to irq_create_mapping()

Marc Zyngier <maz@...nel.org> writes:
> On 2020-11-25 16:24, Laurent Vivier wrote:
>> On 25/11/2020 17:05, Denis Kirjanov wrote:
>>> On 11/25/20, Laurent Vivier <lvivier@...hat.com> wrote:
>>>> With virtio multiqueue, normally each queue IRQ is mapped to a CPU.
>>>> 
>>>> But since commit 0d9f0a52c8b9f ("virtio_scsi: use virtio IRQ 
>>>> affinity")
>>>> this is broken on pseries.
>>> 
>>> Please add "Fixes" tag.
>> 
>> In fact, the code in commit 0d9f0a52c8b9f is correct.
>> 
>> The problem is with MSI/X irq affinity and pseries. So this patch
>> fixes more than virtio_scsi. I put this information because this
>> commit allows to clearly show the problem. Perhaps I should remove
>> this line in fact?
>
> This patch does not fix virtio_scsi at all, which as you noticed, is
> correct. It really fixes the PPC MSI setup, which is starting to show
> its age. So getting rid of the reference seems like the right thing to 
> do.

It's still useful to refer to that commit if the code worked prior to
that commit. But you should make it clearer that 0d9f0a52c8b9f wasn't in
error, it just exposed an existing shortcoming of the arch code.

cheers