Re: [PATCH v2 06/11] vduse: Support automatic irq callback affinity

[Jason Wang <jasowang@redhat.com>]

On Mon, Dec 5, 2022 at 4:59 PM Xie Yongji <xieyongji@bytedance.com> wrote:
>
> This brings current interrupt affinity spreading mechanism
> to vduse device. We will make use of irq_create_affinity_masks()
> to create an irq callback affinity mask for each virtqueue of
> vduse device. Then we will choose the CPU which has the lowest
> number of interrupt allocated in the affinity mask to run the
> irq callback.

This seems a balance mechanism but it might not be the semantic of the
affinity or any reason we need to do this? I guess we should use at
least round-robin in this case.

>
> Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
> ---
>  drivers/vdpa/vdpa_user/vduse_dev.c | 50 ++++++++++++++++++++++++++++++
>  1 file changed, 50 insertions(+)
>
> diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
> index d126f3e32a20..90c2896039d9 100644
> --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> @@ -23,6 +23,7 @@
>  #include <linux/nospec.h>
>  #include <linux/vmalloc.h>
>  #include <linux/sched/mm.h>
> +#include <linux/interrupt.h>
>  #include <uapi/linux/vduse.h>
>  #include <uapi/linux/vdpa.h>
>  #include <uapi/linux/virtio_config.h>
> @@ -58,6 +59,8 @@ struct vduse_virtqueue {
>         struct work_struct inject;
>         struct work_struct kick;
>         int irq_effective_cpu;
> +       struct cpumask irq_affinity;
> +       spinlock_t irq_affinity_lock;

Ok, I'd suggest to squash this into patch 5 to make it more easier to
be reviewed.

>  };
>
>  struct vduse_dev;
> @@ -123,6 +126,7 @@ struct vduse_control {
>
>  static DEFINE_MUTEX(vduse_lock);
>  static DEFINE_IDR(vduse_idr);
> +static DEFINE_PER_CPU(unsigned long, vduse_allocated_irq);
>
>  static dev_t vduse_major;
>  static struct class *vduse_class;
> @@ -710,6 +714,49 @@ static u32 vduse_vdpa_get_generation(struct vdpa_device *vdpa)
>         return dev->generation;
>  }
>
> +static void vduse_vq_update_effective_cpu(struct vduse_virtqueue *vq)
> +{
> +       unsigned int cpu, best_cpu;
> +       unsigned long allocated, allocated_min = UINT_MAX;
> +
> +       spin_lock(&vq->irq_affinity_lock);
> +
> +       best_cpu = vq->irq_effective_cpu;
> +       if (best_cpu != -1)
> +               per_cpu(vduse_allocated_irq, best_cpu) -= 1;
> +
> +       for_each_cpu(cpu, &vq->irq_affinity) {
> +               allocated = per_cpu(vduse_allocated_irq, cpu);
> +               if (!cpu_online(cpu) || allocated >= allocated_min)
> +                       continue;
> +
> +               best_cpu = cpu;
> +               allocated_min = allocated;
> +       }
> +       vq->irq_effective_cpu = best_cpu;
> +       per_cpu(vduse_allocated_irq, best_cpu) += 1;
> +
> +       spin_unlock(&vq->irq_affinity_lock);
> +}
> +
> +static void vduse_vdpa_set_irq_affinity(struct vdpa_device *vdpa,
> +                                       struct irq_affinity *desc)
> +{
> +       struct vduse_dev *dev = vdpa_to_vduse(vdpa);
> +       struct irq_affinity_desc *affd = NULL;
> +       int i;
> +
> +       affd = irq_create_affinity_masks(dev->vq_num, desc);
> +       if (!affd)

Let's add a comment on the vdpa config ops to say set_irq_affinity()
is best effort.

Thanks

> +               return;
> +
> +       for (i = 0; i < dev->vq_num; i++) {
> +               cpumask_copy(&dev->vqs[i]->irq_affinity, &affd[i].mask);
> +               vduse_vq_update_effective_cpu(dev->vqs[i]);
> +       }
> +       kfree(affd);
> +}
> +
>  static int vduse_vdpa_set_map(struct vdpa_device *vdpa,
>                                 unsigned int asid,
>                                 struct vhost_iotlb *iotlb)
> @@ -760,6 +807,7 @@ static const struct vdpa_config_ops vduse_vdpa_config_ops = {
>         .get_config             = vduse_vdpa_get_config,
>         .set_config             = vduse_vdpa_set_config,
>         .get_generation         = vduse_vdpa_get_generation,
> +       .set_irq_affinity       = vduse_vdpa_set_irq_affinity,
>         .reset                  = vduse_vdpa_reset,
>         .set_map                = vduse_vdpa_set_map,
>         .free                   = vduse_vdpa_free,
> @@ -1380,6 +1428,8 @@ static int vduse_dev_init_vqs(struct vduse_dev *dev, u32 vq_align, u32 vq_num)
>                 INIT_WORK(&dev->vqs[i]->kick, vduse_vq_kick_work);
>                 spin_lock_init(&dev->vqs[i]->kick_lock);
>                 spin_lock_init(&dev->vqs[i]->irq_lock);
> +               spin_lock_init(&dev->vqs[i]->irq_affinity_lock);
> +               cpumask_setall(&dev->vqs[i]->irq_affinity);
>         }
>
>         return 0;
> --
> 2.20.1
>