linux-kernel - Re: [PATCH v2 03/11] vdpa: Add set_irq_affinity callback in vdpa_config

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Message-ID: <CACGkMEtoX_jPkJnCB6bx0qkB4pfOAPcSDAdwmd9pL4d8Z3cnEg@mail.gmail.com>
Date:   Mon, 19 Dec 2022 14:06:20 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Yongji Xie <xieyongji@...edance.com>
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Christoph Hellwig <hch@....de>,
        virtualization <virtualization@...ts.linux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 03/11] vdpa: Add set_irq_affinity callback in vdpa_config_ops

On Mon, Dec 19, 2022 at 12:39 PM Yongji Xie <xieyongji@...edance.com> wrote:
>
> On Fri, Dec 16, 2022 at 11:58 AM Jason Wang <jasowang@...hat.com> wrote:
> >
> > On Mon, Dec 5, 2022 at 4:43 PM Xie Yongji <xieyongji@...edance.com> wrote:
> > >
> > > This introduces set_irq_affinity callback in
> > > vdpa_config_ops so that vdpa device driver can
> > > get the interrupt affinity hint from the virtio
> > > device driver. The interrupt affinity hint would
> > > be needed by the interrupt affinity spreading
> > > mechanism.
> > >
> > > Signed-off-by: Xie Yongji <xieyongji@...edance.com>
> > > ---
> > >  drivers/virtio/virtio_vdpa.c | 4 ++++
> > >  include/linux/vdpa.h         | 8 ++++++++
> > >  2 files changed, 12 insertions(+)
> > >
> > > diff --git a/drivers/virtio/virtio_vdpa.c b/drivers/virtio/virtio_vdpa.c
> > > index 08084b49e5a1..4731e4616ee0 100644
> > > --- a/drivers/virtio/virtio_vdpa.c
> > > +++ b/drivers/virtio/virtio_vdpa.c
> > > @@ -275,9 +275,13 @@ static int virtio_vdpa_find_vqs(struct virtio_device *vdev, unsigned int nvqs,
> > >         struct virtio_vdpa_device *vd_dev = to_virtio_vdpa_device(vdev);
> > >         struct vdpa_device *vdpa = vd_get_vdpa(vdev);
> > >         const struct vdpa_config_ops *ops = vdpa->config;
> > > +       struct irq_affinity default_affd = { 0 };
> > >         struct vdpa_callback cb;
> > >         int i, err, queue_idx = 0;
> > >
> > > +       if (ops->set_irq_affinity)
> > > +               ops->set_irq_affinity(vdpa, desc ? desc : &default_affd);
> >
> > I wonder if we need to do this in vhost-vDPA.
>
> I don't get why we need to do this in vhost-vDPA? Should this be done in VM?

If I was not wrong, this tries to set affinity on the host instead of
the guest. More below.

>
> > Or it's better to have a
> > default affinity by the vDPA parent
> >
>
> I think both are OK. But the default value should always be zero, so I
> put it in a common place.

I think we should either:

1) document the zero default value in vdpa.c
2) set the zero in both vhost-vdpa and virtio-vdpa, or in the vdpa core

>
> > (Looking at virtio-pci, it doesn't do something like this).
> >
>
> Yes, but we did something like this in the pci layer:
> pci_alloc_irq_vectors_affinity().

Ok.

Thanks

>
> Thanks,
> Yongji
>