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

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Date:   Mon, 19 Dec 2022 12:38:58 +0800
From:   Yongji Xie <xieyongji@...edance.com>
To:     Jason Wang <jasowang@...hat.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 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?

> 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.

> (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().

Thanks,
Yongji