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

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Date:   Wed, 25 Nov 2020 16:42:30 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     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>,
        Michael Ellerman <mpe@...erman.id.au>,
        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()

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.

I'm also not keen on the BugId thing. It should really be a lore link.
I also cannot find any such tag in the kernel, nor is it a documented
practice. The last reference to a Bugzilla entry seems to have happened
with 786b5219081ff16 (five years ago).

Thanks,

         M.
-- 
Jazz is not dead. It just smells funny...