[virtio-dev] [PATCH v1 09/12] drm/virtio: implement context init: allocate an array of fence contexts
Gurchetan Singh
gurchetansingh at chromium.org
Wed Sep 15 01:25:46 UTC 2021
On Tue, Sep 14, 2021 at 10:53 AM Chia-I Wu <olvaffe at gmail.com> wrote:
> ,On Mon, Sep 13, 2021 at 6:57 PM Gurchetan Singh
> <gurchetansingh at chromium.org> wrote:
> >
> >
> >
> >
> > On Mon, Sep 13, 2021 at 11:52 AM Chia-I Wu <olvaffe at gmail.com> wrote:
> >>
> >> .
> >>
> >> On Mon, Sep 13, 2021 at 10:48 AM Gurchetan Singh
> >> <gurchetansingh at chromium.org> wrote:
> >> >
> >> >
> >> >
> >> > On Fri, Sep 10, 2021 at 12:33 PM Chia-I Wu <olvaffe at gmail.com> wrote:
> >> >>
> >> >> On Wed, Sep 8, 2021 at 6:37 PM Gurchetan Singh
> >> >> <gurchetansingh at 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 at chromium.org>
> >> >> > Acked-by: Lingfeng Yang <lfy at 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)?
> >>
> >> Fences can be implicitly shared via reservation objects associated
> >> with 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.
> >>
> >> Right, that's what I am looking for. Userspace expects implicit
> >> fencing to work. While there are works to move the userspace to do
> >> explicit fencing, it is not there yet in general and we can't require
> >> the userspace to do explicit fencing or DRM_IOCTL_VIRTGPU_WAIT.
> >
> >
> > Another option would be to use the upcoming
> DMA_BUF_IOCTL_EXPORT_SYNC_FILE + VIRTGPU_EXECBUF_FENCE_FD_IN (which checks
> the dma_fence context).
> That requires the X server / compositors to be modified. For example,
> venus works under Android (where there is explicit fencing) or under a
> modified compositor (which does DMA_BUF_IOCTL_EXPORT_SYNC_FILE or
> DRM_IOCTL_VIRTGPU_WAIT). But it does not work too well with an
> unmodified X server.
>
Some semi-recent virgl modifications will be needed regardless for interop,
such as VIRGL_CAP_V2_UNTYPED_RESOURCE (?).
Not sure aren't too many virgl users (most developers)
Does Xserver just pick up the latest Mesa release (including virgl/venus)?
Suppose context types land in 5.16, the userspace changes land (both
Venus/Virgl) in 21.2 stable releases.
https://docs.mesa3d.org/release-calendar.html
> >
> > Generally, if it only requires virgl changes, userspace changes are fine
> since OpenGL drivers implement implicit sync in many ways. Waiting on the
> reservation object in the kernel is fine too though.
> I don't think we want to assume virgl to be the only consumer of
> dma-bufs, despite that it is the most common use case.
> >
> > Though venus doesn't use the NUM_RINGS param yet. Getting all
> permutations of context type + display integration working would take some
> time (patchset mostly tested with wayland + gfxstream/Android [no implicit
> sync]).
> >
> > WDYT of someone figuring out virgl/venus interop later, independently of
> this patchset?
>
> I think we should understand the implications of multiple fence
> contexts better, even if some changes are not included in this
> patchset.
>
> From my view, we don't need implicit fencing in most cases and
> implicit fencing should be considered a legacy path. But X server /
> compositors today happen to require it. Other drivers seem to use a
> flag to control whether implicit fences are set up or waited (e.g.,
> AMDGPU_GEM_CREATE_EXPLICIT_SYNC, MSM_SUBMIT_NO_IMPLICIT, or
> EXEC_OBJECT_WRITE). It seems to be the least surprising thing to do.
>
IMO, the easiest way is just to limit the change to userspace if possible
since implicit sync is legacy/something we want to deprecate over time.
Another option is to add something like VIRTGPU_EXECBUF_EXPLICIT_SYNC
(similar to MSM_SUBMIT_NO_IMPLICIT), where the reservation objects are
waited on / added to without that flag. Since explicit sync will need new
hypercalls/params and is a major, that feature is expected to be
independent of context types.
With that option, waiting on the reservation object would just be another
bug fix + addition to 5.16 (perhaps by you) so we can proceed in parallel
faster. VIRTGPU_EXECBUF_EXPLICIT_SYNC (or an equivalent) would be added
later.
>
> >
> >>
> >>
> >>
> >>
> >> >
> >> >>
> >> >>
> >> >> > + vfpriv->num_rings = value;
> >> >> > + break;
> >> >> > default:
> >> >> > ret = -EINVAL;
> >> >> > goto out_unlock;
> >> >> > --
> >> >> > 2.33.0.153.gba50c8fa24-goog
> >> >> >
> >> >> >
> >> >> >
> ---------------------------------------------------------------------
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> >> >> > For additional commands, e-mail:
> virtio-dev-help at lists.oasis-open.org
> >> >> >
>
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