Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> writes:
> If we want to reuse a fence that is in active use by the GPU, we have to
> wait an uncertain amount of time, but if we reuse an inactive fence, we
> can change it right away. Loop through the list of available fences
> twice, ignoring any active fences on the first pass.
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Mika Kuoppala <mika.kuoppala@xxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/gt/intel_ggtt_fencing.c | 22 ++++++++++++++++++--
> 1 file changed, 20 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_ggtt_fencing.c b/drivers/gpu/drm/i915/gt/intel_ggtt_fencing.c
> index 7fb36b12fe7a..a357bb431815 100644
> --- a/drivers/gpu/drm/i915/gt/intel_ggtt_fencing.c
> +++ b/drivers/gpu/drm/i915/gt/intel_ggtt_fencing.c
> @@ -320,13 +320,31 @@ void i915_vma_revoke_fence(struct i915_vma *vma)
> fence_write(fence);
> }
>
> +static bool fence_is_active(const struct i915_fence_reg *fence)
> +{
> + return fence->vma && i915_vma_is_active(fence->vma);
> +}
> +
> static struct i915_fence_reg *fence_find(struct i915_ggtt *ggtt)
> {
> - struct i915_fence_reg *fence;
> + struct i915_fence_reg *active = NULL;
> + struct i915_fence_reg *fence, *fn;
>
> - list_for_each_entry(fence, &ggtt->fence_list, link) {
> + list_for_each_entry_safe(fence, fn, &ggtt->fence_list, link) {
> GEM_BUG_ON(fence->vma && fence->vma->fence != fence);
>
> + if (fence == active) /* now seen this fence twice */
> + active = ERR_PTR(-EAGAIN);
> +
> + /* Prefer idle fences so we do not have to wait on the GPU */
> + if (active != ERR_PTR(-EAGAIN) && fence_is_active(fence)) {
> + if (!active)
> + active = fence;
> +
> + list_move_tail(&fence->link, &ggtt->fence_list);
> + continue;
> + }
> +
> if (atomic_read(&fence->pin_count))
> continue;
>
> --
> 2.20.1
>
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