Re: [Intel-gfx] [PATCH v10 09/15] drm/syncobj: Add deadline support for syncobj waits

[Faith Ekstrand <faith@gfxstrand.net>]

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On Wed, Mar 8, 2023 at 9:54 AM Rob Clark <robdclark@gmail.com> wrote:

> From: Rob Clark <robdclark@chromium.org>
>
> Add a new flag to let userspace provide a deadline as a hint for syncobj
> and timeline waits.  This gives a hint to the driver signaling the
> backing fences about how soon userspace needs it to compete work, so it
> can addjust GPU frequency accordingly.  An immediate deadline can be
> given to provide something equivalent to i915 "wait boost".
>
> v2: Use absolute u64 ns value for deadline hint, drop cap and driver
>     feature flag in favor of allowing count_handles==0 as a way for
>     userspace to probe kernel for support of new flag
> v3: More verbose comments about UAPI
>
> Signed-off-by: Rob Clark <robdclark@chromium.org>
> ---
>  drivers/gpu/drm/drm_syncobj.c | 64 ++++++++++++++++++++++++++++-------
>  include/uapi/drm/drm.h        | 17 ++++++++++
>  2 files changed, 68 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
> index 0c2be8360525..a85e9464f07b 100644
> --- a/drivers/gpu/drm/drm_syncobj.c
> +++ b/drivers/gpu/drm/drm_syncobj.c
> @@ -126,6 +126,11 @@
>   * synchronize between the two.
>   * This requirement is inherited from the Vulkan fence API.
>   *
> + * If &DRM_SYNCOBJ_WAIT_FLAGS_WAIT_DEADLINE is set, the ioctl will also
> set
> + * a fence deadline hint on the backing fences before waiting, to provide
> the
> + * fence signaler with an appropriate sense of urgency.  The deadline is
> + * specified as an absolute &CLOCK_MONOTONIC value in units of ns.
> + *
>   * Similarly, &DRM_IOCTL_SYNCOBJ_TIMELINE_WAIT takes an array of syncobj
>   * handles as well as an array of u64 points and does a host-side wait on
> all
>   * of syncobj fences at the given points simultaneously.
> @@ -973,7 +978,8 @@ static signed long
> drm_syncobj_array_wait_timeout(struct drm_syncobj **syncobjs,
>                                                   uint32_t count,
>                                                   uint32_t flags,
>                                                   signed long timeout,
> -                                                 uint32_t *idx)
> +                                                 uint32_t *idx,
> +                                                 ktime_t *deadline)
>  {
>         struct syncobj_wait_entry *entries;
>         struct dma_fence *fence;
> @@ -1053,6 +1059,15 @@ static signed long
> drm_syncobj_array_wait_timeout(struct drm_syncobj **syncobjs,
>                         drm_syncobj_fence_add_wait(syncobjs[i],
> &entries[i]);
>         }
>
> +       if (deadline) {
> +               for (i = 0; i < count; ++i) {
> +                       fence = entries[i].fence;
> +                       if (!fence)
> +                               continue;
> +                       dma_fence_set_deadline(fence, *deadline);
> +               }
> +       }
> +
>         do {
>                 set_current_state(TASK_INTERRUPTIBLE);
>
> @@ -1151,7 +1166,8 @@ static int drm_syncobj_array_wait(struct drm_device
> *dev,
>                                   struct drm_file *file_private,
>                                   struct drm_syncobj_wait *wait,
>                                   struct drm_syncobj_timeline_wait
> *timeline_wait,
> -                                 struct drm_syncobj **syncobjs, bool
> timeline)
> +                                 struct drm_syncobj **syncobjs, bool
> timeline,
> +                                 ktime_t *deadline)
>  {
>         signed long timeout = 0;
>         uint32_t first = ~0;
> @@ -1162,7 +1178,8 @@ static int drm_syncobj_array_wait(struct drm_device
> *dev,
>                                                          NULL,
>
>  wait->count_handles,
>                                                          wait->flags,
> -                                                        timeout, &first);
> +                                                        timeout, &first,
> +                                                        deadline);
>                 if (timeout < 0)
>                         return timeout;
>                 wait->first_signaled = first;
> @@ -1172,7 +1189,8 @@ static int drm_syncobj_array_wait(struct drm_device
> *dev,
>
>  u64_to_user_ptr(timeline_wait->points),
>
>  timeline_wait->count_handles,
>
>  timeline_wait->flags,
> -                                                        timeout, &first);
> +                                                        timeout, &first,
> +                                                        deadline);
>                 if (timeout < 0)
>                         return timeout;
>                 timeline_wait->first_signaled = first;
> @@ -1243,17 +1261,22 @@ drm_syncobj_wait_ioctl(struct drm_device *dev,
> void *data,
>  {
>         struct drm_syncobj_wait *args = data;
>         struct drm_syncobj **syncobjs;
> +       unsigned possible_flags;
> +       ktime_t t, *tp = NULL;
>         int ret = 0;
>
>         if (!drm_core_check_feature(dev, DRIVER_SYNCOBJ))
>                 return -EOPNOTSUPP;
>
> -       if (args->flags & ~(DRM_SYNCOBJ_WAIT_FLAGS_WAIT_ALL |
> -                           DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT))
> +       possible_flags = DRM_SYNCOBJ_WAIT_FLAGS_WAIT_ALL |
> +                        DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT |
> +                        DRM_SYNCOBJ_WAIT_FLAGS_WAIT_DEADLINE;
> +
> +       if (args->flags & ~possible_flags)
>                 return -EINVAL;
>
>         if (args->count_handles == 0)
> -               return -EINVAL;
> +               return 0;
>

Did you intend this change? If so, why? What does waiting with no handles
gain us? I mean, it's probably fine but it seems unrelated to this change.

        ret = drm_syncobj_array_find(file_private,
>                                      u64_to_user_ptr(args->handles),
> @@ -1262,8 +1285,13 @@ drm_syncobj_wait_ioctl(struct drm_device *dev, void
> *data,
>         if (ret < 0)
>                 return ret;
>
> +       if (args->flags & DRM_SYNCOBJ_WAIT_FLAGS_WAIT_DEADLINE) {
> +               t = ns_to_ktime(args->deadline_ns);
> +               tp = &t;
> +       }
> +
>         ret = drm_syncobj_array_wait(dev, file_private,
> -                                    args, NULL, syncobjs, false);
> +                                    args, NULL, syncobjs, false, tp);
>
>         drm_syncobj_array_free(syncobjs, args->count_handles);
>
> @@ -1276,18 +1304,23 @@ drm_syncobj_timeline_wait_ioctl(struct drm_device
> *dev, void *data,
>  {
>         struct drm_syncobj_timeline_wait *args = data;
>         struct drm_syncobj **syncobjs;
> +       unsigned possible_flags;
> +       ktime_t t, *tp = NULL;
>         int ret = 0;
>
>         if (!drm_core_check_feature(dev, DRIVER_SYNCOBJ_TIMELINE))
>                 return -EOPNOTSUPP;
>
> -       if (args->flags & ~(DRM_SYNCOBJ_WAIT_FLAGS_WAIT_ALL |
> -                           DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT |
> -                           DRM_SYNCOBJ_WAIT_FLAGS_WAIT_AVAILABLE))
> +       possible_flags = DRM_SYNCOBJ_WAIT_FLAGS_WAIT_ALL |
> +                        DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT |
> +                        DRM_SYNCOBJ_WAIT_FLAGS_WAIT_AVAILABLE |
> +                        DRM_SYNCOBJ_WAIT_FLAGS_WAIT_DEADLINE;
> +
> +       if (args->flags & ~possible_flags)
>                 return -EINVAL;
>
>         if (args->count_handles == 0)
> -               return -EINVAL;
> +               return -0;
>

Did you intend this change? -0 is a pretty weird integer.


>         ret = drm_syncobj_array_find(file_private,
>                                      u64_to_user_ptr(args->handles),
> @@ -1296,8 +1329,13 @@ drm_syncobj_timeline_wait_ioctl(struct drm_device
> *dev, void *data,
>         if (ret < 0)
>                 return ret;
>
> +       if (args->flags & DRM_SYNCOBJ_WAIT_FLAGS_WAIT_DEADLINE) {
> +               t = ns_to_ktime(args->deadline_ns);
> +               tp = &t;
> +       }
> +
>         ret = drm_syncobj_array_wait(dev, file_private,
> -                                    NULL, args, syncobjs, true);
> +                                    NULL, args, syncobjs, true, tp);
>
>         drm_syncobj_array_free(syncobjs, args->count_handles);
>
> diff --git a/include/uapi/drm/drm.h b/include/uapi/drm/drm.h
> index 642808520d92..bff0509ac8b6 100644
> --- a/include/uapi/drm/drm.h
> +++ b/include/uapi/drm/drm.h
> @@ -887,6 +887,7 @@ struct drm_syncobj_transfer {
>  #define DRM_SYNCOBJ_WAIT_FLAGS_WAIT_ALL (1 << 0)
>  #define DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT (1 << 1)
>  #define DRM_SYNCOBJ_WAIT_FLAGS_WAIT_AVAILABLE (1 << 2) /* wait for time
> point to become available */
> +#define DRM_SYNCOBJ_WAIT_FLAGS_WAIT_DEADLINE (1 << 3) /* set fence
> deadline based to deadline_ns */
>  struct drm_syncobj_wait {
>         __u64 handles;
>         /* absolute timeout */
> @@ -895,6 +896,14 @@ struct drm_syncobj_wait {
>         __u32 flags;
>         __u32 first_signaled; /* only valid when not waiting all */
>         __u32 pad;
> +       /**
> +        * @deadline_ns - fence deadline hint
> +        *
> +        * Deadline hint, in absolute CLOCK_MONOTONIC, to set on backing
> +        * fence(s) if the DRM_SYNCOBJ_WAIT_FLAGS_WAIT_DEADLINE flag is
> +        * set.
> +        */
> +       __u64 deadline_ns;
>  };
>
>  struct drm_syncobj_timeline_wait {
> @@ -907,6 +916,14 @@ struct drm_syncobj_timeline_wait {
>         __u32 flags;
>         __u32 first_signaled; /* only valid when not waiting all */
>         __u32 pad;
> +       /**
> +        * @deadline_ns - fence deadline hint
> +        *
> +        * Deadline hint, in absolute CLOCK_MONOTONIC, to set on backing
> +        * fence(s) if the DRM_SYNCOBJ_WAIT_FLAGS_WAIT_DEADLINE flag is
> +        * set.
> +        */
> +       __u64 deadline_ns;
>  };
>
>
> --
> 2.39.2
>
>

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