Re: [virtio-dev] [PATCH v1 09/12] drm/virtio: implement context init: allocate an array of fence contexts

[Gurchetan Singh <gurchetansingh@chromium.org>]

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On Fri, Sep 10, 2021 at 12:33 PM Chia-I Wu <olvaffe@gmail.com> wrote:

> On Wed, Sep 8, 2021 at 6:37 PM Gurchetan Singh
> <gurchetansingh@chromium.org> wrote:
> >
> > We don't want fences from different 3D contexts (virgl, gfxstream,
> > venus) to be on the same timeline.  With explicit context creation,
> > we can specify the number of ring each context wants.
> >
> > Execbuffer can specify which ring to use.
> >
> > Signed-off-by: Gurchetan Singh <gurchetansingh@chromium.org>
> > Acked-by: Lingfeng Yang <lfy@google.com>
> > ---
> >  drivers/gpu/drm/virtio/virtgpu_drv.h   |  3 +++
> >  drivers/gpu/drm/virtio/virtgpu_ioctl.c | 34 ++++++++++++++++++++++++--
> >  2 files changed, 35 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.h
> b/drivers/gpu/drm/virtio/virtgpu_drv.h
> > index a5142d60c2fa..cca9ab505deb 100644
> > --- a/drivers/gpu/drm/virtio/virtgpu_drv.h
> > +++ b/drivers/gpu/drm/virtio/virtgpu_drv.h
> > @@ -56,6 +56,7 @@
> >  #define STATE_ERR 2
> >
> >  #define MAX_CAPSET_ID 63
> > +#define MAX_RINGS 64
> >
> >  struct virtio_gpu_object_params {
> >         unsigned long size;
> > @@ -263,6 +264,8 @@ struct virtio_gpu_fpriv {
> >         uint32_t ctx_id;
> >         uint32_t context_init;
> >         bool context_created;
> > +       uint32_t num_rings;
> > +       uint64_t base_fence_ctx;
> >         struct mutex context_lock;
> >  };
> >
> > diff --git a/drivers/gpu/drm/virtio/virtgpu_ioctl.c
> b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
> > index f51f3393a194..262f79210283 100644
> > --- a/drivers/gpu/drm/virtio/virtgpu_ioctl.c
> > +++ b/drivers/gpu/drm/virtio/virtgpu_ioctl.c
> > @@ -99,6 +99,11 @@ static int virtio_gpu_execbuffer_ioctl(struct
> drm_device *dev, void *data,
> >         int in_fence_fd = exbuf->fence_fd;
> >         int out_fence_fd = -1;
> >         void *buf;
> > +       uint64_t fence_ctx;
> > +       uint32_t ring_idx;
> > +
> > +       fence_ctx = vgdev->fence_drv.context;
> > +       ring_idx = 0;
> >
> >         if (vgdev->has_virgl_3d == false)
> >                 return -ENOSYS;
> > @@ -106,6 +111,17 @@ static int virtio_gpu_execbuffer_ioctl(struct
> drm_device *dev, void *data,
> >         if ((exbuf->flags & ~VIRTGPU_EXECBUF_FLAGS))
> >                 return -EINVAL;
> >
> > +       if ((exbuf->flags & VIRTGPU_EXECBUF_RING_IDX)) {
> > +               if (exbuf->ring_idx >= vfpriv->num_rings)
> > +                       return -EINVAL;
> > +
> > +               if (!vfpriv->base_fence_ctx)
> > +                       return -EINVAL;
> > +
> > +               fence_ctx = vfpriv->base_fence_ctx;
> > +               ring_idx = exbuf->ring_idx;
> > +       }
> > +
> >         exbuf->fence_fd = -1;
> >
> >         virtio_gpu_create_context(dev, file);
> > @@ -173,7 +189,7 @@ static int virtio_gpu_execbuffer_ioctl(struct
> drm_device *dev, void *data,
> >                         goto out_memdup;
> >         }
> >
> > -       out_fence = virtio_gpu_fence_alloc(vgdev,
> vgdev->fence_drv.context, 0);
> > +       out_fence = virtio_gpu_fence_alloc(vgdev, fence_ctx, ring_idx);
> >         if(!out_fence) {
> >                 ret = -ENOMEM;
> >                 goto out_unresv;
> > @@ -691,7 +707,7 @@ static int virtio_gpu_context_init_ioctl(struct
> drm_device *dev,
> >                 return -EINVAL;
> >
> >         /* Number of unique parameters supported at this time. */
> > -       if (num_params > 1)
> > +       if (num_params > 2)
> >                 return -EINVAL;
> >
> >         ctx_set_params =
> memdup_user(u64_to_user_ptr(args->ctx_set_params),
> > @@ -731,6 +747,20 @@ static int virtio_gpu_context_init_ioctl(struct
> drm_device *dev,
> >
> >                         vfpriv->context_init |= value;
> >                         break;
> > +               case VIRTGPU_CONTEXT_PARAM_NUM_RINGS:
> > +                       if (vfpriv->base_fence_ctx) {
> > +                               ret = -EINVAL;
> > +                               goto out_unlock;
> > +                       }
> > +
> > +                       if (value > MAX_RINGS) {
> > +                               ret = -EINVAL;
> > +                               goto out_unlock;
> > +                       }
> > +
> > +                       vfpriv->base_fence_ctx =
> dma_fence_context_alloc(value);
> With multiple fence contexts, we should do something about implicit
> fencing.
>
> The classic example is Mesa and X server.  When both use virgl and the
> global fence context, no dma_fence_wait is fine.  But when Mesa uses
> venus and the ring fence context, dma_fence_wait should be inserted.
>

 If I read your comment correctly, the use case is:

context A (venus)

sharing a render target with

context B (Xserver backed virgl)

?

Which function do you envisage dma_fence_wait(...) to be inserted?  Doesn't
implicit synchronization mean there's no fence to share between contexts
(only buffer objects)?

It may be possible to wait on the reservation object associated with a
buffer object from a different context (userspace can also do
DRM_IOCTL_VIRTGPU_WAIT), but not sure if that's what you're looking for.


>
> > +                       vfpriv->num_rings = value;
> > +                       break;
> >                 default:
> >                         ret = -EINVAL;
> >                         goto out_unlock;
> > --
> > 2.33.0.153.gba50c8fa24-goog
> >
> >
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> >
>

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