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From:   Jason Wang <jasowang@redhat.com>
Date:   Tue, 20 Dec 2022 14:27:44 +0800
Message-ID: <CACGkMEt1MkoxJQUixMsR8gVmTVUVoPh1CNo7GpbOyWGb3bzoPw@mail.gmail.com>
Subject: Re: [PATCH v2 05/11] vduse: Introduce bound workqueue for irq injection
To:     Yongji Xie <xieyongji@bytedance.com>
Cc:     "Michael S. Tsirkin" <mst@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Christoph Hellwig <hch@lst.de>,
        virtualization <virtualization@lists.linux-foundation.org>,
        linux-kernel <linux-kernel@vger.kernel.org>
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On Mon, Dec 19, 2022 at 1:04 PM Yongji Xie <xieyongji@bytedance.com> wrote:
>
> On Fri, Dec 16, 2022 at 12:02 PM Jason Wang <jasowang@redhat.com> wrote:
> >
> > On Mon, Dec 5, 2022 at 4:44 PM Xie Yongji <xieyongji@bytedance.com> wrote:
> > >
> > > This introduces a bound workqueue to support running
> > > irq callback in a specified cpu.
> > >
> > > Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
> > > ---
> > >  drivers/vdpa/vdpa_user/vduse_dev.c | 29 ++++++++++++++++++++++-------
> > >  1 file changed, 22 insertions(+), 7 deletions(-)
> > >
> > > diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
> > > index 37809bfcb7ef..d126f3e32a20 100644
> > > --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> > > +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> > > @@ -57,6 +57,7 @@ struct vduse_virtqueue {
> > >         struct vdpa_callback cb;
> > >         struct work_struct inject;
> > >         struct work_struct kick;
> > > +       int irq_effective_cpu;
> >
> > I wonder why it's a cpu number instead of a cpumask. The latter seems
> > more flexible, e.g when using NUMA.
> >
>
> This variable represents the CPU that runs the interrupt callback
> rather than CPU affinity.

Ok, but for some reason it only gets updated when a new affinity is set?

(Btw, I don't see how the code deals with cpu hotplug, do we need
cpuhot notifier?)

Thanks

>
> > >  };
> > >
> > >  struct vduse_dev;
> > > @@ -128,6 +129,7 @@ static struct class *vduse_class;
> > >  static struct cdev vduse_ctrl_cdev;
> > >  static struct cdev vduse_cdev;
> > >  static struct workqueue_struct *vduse_irq_wq;
> > > +static struct workqueue_struct *vduse_irq_bound_wq;
> > >
> > >  static u32 allowed_device_id[] = {
> > >         VIRTIO_ID_BLOCK,
> > > @@ -917,7 +919,8 @@ static void vduse_vq_irq_inject(struct work_struct *work)
> > >  }
> > >
> > >  static int vduse_dev_queue_irq_work(struct vduse_dev *dev,
> > > -                                   struct work_struct *irq_work)
> > > +                                   struct work_struct *irq_work,
> > > +                                   int irq_effective_cpu)
> > >  {
> > >         int ret = -EINVAL;
> > >
> > > @@ -926,7 +929,11 @@ static int vduse_dev_queue_irq_work(struct vduse_dev *dev,
> > >                 goto unlock;
> > >
> > >         ret = 0;
> > > -       queue_work(vduse_irq_wq, irq_work);
> > > +       if (irq_effective_cpu == -1)
> >
> > Is it better to have a macro for this magic number?
> >
>
> It makes sense to me.
>
> Thanks,
> Yongji
>