Re: [PATCH] nouveau: rip out busy fence waits

[Ben Skeggs <bskeggs@xxxxxxxxxx>]

On 17/4/24 15:40, Dave Airlie wrote:

> External email: Use caution opening links or attachments
>
>
> From: Dave Airlie <airlied@xxxxxxxxxx>
>
> I'm pretty sure this optimisation is actually not a great idea,
> and is racy with other things waiting for fences.
>
> Just nuke it, there should be no need to do fence waits in a
> busy CPU loop.
>
> Signed-off-by: Dave Airlie <airlied@xxxxxxxxxx>

Reviewed-by: Ben Skeggs <bskeggs@xxxxxxxxxx>


> ---
>   drivers/gpu/drm/nouveau/nouveau_bo.c    |  2 +-
>   drivers/gpu/drm/nouveau/nouveau_chan.c  |  2 +-
>   drivers/gpu/drm/nouveau/nouveau_dmem.c  |  2 +-
>   drivers/gpu/drm/nouveau/nouveau_fence.c | 30 +------------------------
>   drivers/gpu/drm/nouveau/nouveau_fence.h |  2 +-
>   drivers/gpu/drm/nouveau/nouveau_gem.c   |  2 +-
>   6 files changed, 6 insertions(+), 34 deletions(-)
>
> diff --git a/drivers/gpu/drm/nouveau/nouveau_bo.c b/drivers/gpu/drm/nouveau/nouveau_bo.c
> index 8a30f5a0525b..a4e8f625fce6 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_bo.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_bo.c
> @@ -902,7 +902,7 @@ nouveau_bo_move_m2mf(struct ttm_buffer_object *bo, int evict,
>           * Without this the operation can timeout and we'll fallback to a
>           * software copy, which might take several minutes to finish.
>           */
> -       nouveau_fence_wait(fence, false, false);
> +       nouveau_fence_wait(fence, false);
>          ret = ttm_bo_move_accel_cleanup(bo, &fence->base, evict, false,
>                                          new_reg);
>          nouveau_fence_unref(&fence);
> diff --git a/drivers/gpu/drm/nouveau/nouveau_chan.c b/drivers/gpu/drm/nouveau/nouveau_chan.c
> index 7c97b2886807..66fca95c10c7 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_chan.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_chan.c
> @@ -72,7 +72,7 @@ nouveau_channel_idle(struct nouveau_channel *chan)
>
>                  ret = nouveau_fence_new(&fence, chan);
>                  if (!ret) {
> -                       ret = nouveau_fence_wait(fence, false, false);
> +                       ret = nouveau_fence_wait(fence, false);
>                          nouveau_fence_unref(&fence);
>                  }
>
> diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c b/drivers/gpu/drm/nouveau/nouveau_dmem.c
> index 12feecf71e75..033a09cd3c8f 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
> @@ -128,7 +128,7 @@ static void nouveau_dmem_page_free(struct page *page)
>   static void nouveau_dmem_fence_done(struct nouveau_fence **fence)
>   {
>          if (fence) {
> -               nouveau_fence_wait(*fence, true, false);
> +               nouveau_fence_wait(*fence, false);
>                  nouveau_fence_unref(fence);
>          } else {
>                  /*
> diff --git a/drivers/gpu/drm/nouveau/nouveau_fence.c b/drivers/gpu/drm/nouveau/nouveau_fence.c
> index c3ea3cd933cd..8de941379324 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_fence.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_fence.c
> @@ -312,39 +312,11 @@ nouveau_fence_wait_legacy(struct dma_fence *f, bool intr, long wait)
>          return timeout - t;
>   }
>
> -static int
> -nouveau_fence_wait_busy(struct nouveau_fence *fence, bool intr)
> -{
> -       int ret = 0;
> -
> -       while (!nouveau_fence_done(fence)) {
> -               if (time_after_eq(jiffies, fence->timeout)) {
> -                       ret = -EBUSY;
> -                       break;
> -               }
> -
> -               __set_current_state(intr ?
> -                                   TASK_INTERRUPTIBLE :
> -                                   TASK_UNINTERRUPTIBLE);
> -
> -               if (intr && signal_pending(current)) {
> -                       ret = -ERESTARTSYS;
> -                       break;
> -               }
> -       }
> -
> -       __set_current_state(TASK_RUNNING);
> -       return ret;
> -}
> -
>   int
> -nouveau_fence_wait(struct nouveau_fence *fence, bool lazy, bool intr)
> +nouveau_fence_wait(struct nouveau_fence *fence, bool intr)
>   {
>          long ret;
>
> -       if (!lazy)
> -               return nouveau_fence_wait_busy(fence, intr);
> -
>          ret = dma_fence_wait_timeout(&fence->base, intr, 15 * HZ);
>          if (ret < 0)
>                  return ret;
> diff --git a/drivers/gpu/drm/nouveau/nouveau_fence.h b/drivers/gpu/drm/nouveau/nouveau_fence.h
> index bc13110bdfa4..88213014b675 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_fence.h
> +++ b/drivers/gpu/drm/nouveau/nouveau_fence.h
> @@ -23,7 +23,7 @@ void nouveau_fence_unref(struct nouveau_fence **);
>
>   int  nouveau_fence_emit(struct nouveau_fence *);
>   bool nouveau_fence_done(struct nouveau_fence *);
> -int  nouveau_fence_wait(struct nouveau_fence *, bool lazy, bool intr);
> +int  nouveau_fence_wait(struct nouveau_fence *, bool intr);
>   int  nouveau_fence_sync(struct nouveau_bo *, struct nouveau_channel *, bool exclusive, bool intr);
>
>   struct nouveau_fence_chan {
> diff --git a/drivers/gpu/drm/nouveau/nouveau_gem.c b/drivers/gpu/drm/nouveau/nouveau_gem.c
> index 49c2bcbef129..f715e381da69 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_gem.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_gem.c
> @@ -928,7 +928,7 @@ nouveau_gem_ioctl_pushbuf(struct drm_device *dev, void *data,
>          }
>
>          if (sync) {
> -               if (!(ret = nouveau_fence_wait(fence, false, false))) {
> +               if (!(ret = nouveau_fence_wait(fence, false))) {
>                          if ((ret = dma_fence_get_status(&fence->base)) == 1)
>                                  ret = 0;
>                  }
> --
> 2.43.2