Quoting Christian König (2019-08-07 14:53:11)
> Other cores don't busy wait any more and we removed the last user of checking
> the seqno for changes. Drop updating the number for shared fences altogether.
>
> Signed-off-by: Christian König <christian.koenig@xxxxxxx>
Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> ---
> drivers/dma-buf/reservation.c | 6 ------
> drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c | 7 +------
> 2 files changed, 1 insertion(+), 12 deletions(-)
>
> diff --git a/drivers/dma-buf/reservation.c b/drivers/dma-buf/reservation.c
> index 8fcaddffd5d4..90bc6ef03598 100644
> --- a/drivers/dma-buf/reservation.c
> +++ b/drivers/dma-buf/reservation.c
> @@ -237,9 +237,6 @@ void reservation_object_add_shared_fence(struct reservation_object *obj,
> fobj = reservation_object_get_list(obj);
> count = fobj->shared_count;
>
> - preempt_disable();
> - write_seqcount_begin(&obj->seq);
> -
> for (i = 0; i < count; ++i) {
>
> old = rcu_dereference_protected(fobj->shared[i],
> @@ -257,9 +254,6 @@ void reservation_object_add_shared_fence(struct reservation_object *obj,
> RCU_INIT_POINTER(fobj->shared[i], fence);
> /* pointer update must be visible before we extend the shared_count */
> smp_store_mb(fobj->shared_count, count);
> -
> - write_seqcount_end(&obj->seq);
> - preempt_enable();
> dma_fence_put(old);
> }
> EXPORT_SYMBOL(reservation_object_add_shared_fence);
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
> index fe062b76ec91..a4640ddc24d1 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c
> @@ -251,12 +251,7 @@ static int amdgpu_amdkfd_remove_eviction_fence(struct amdgpu_bo *bo,
> new->shared_max = old->shared_max;
> new->shared_count = k;
>
> - /* Install the new fence list, seqcount provides the barriers */
> - preempt_disable();
> - write_seqcount_begin(&resv->seq);
> - RCU_INIT_POINTER(resv->fence, new);
> - write_seqcount_end(&resv->seq);
> - preempt_enable();
> + rcu_assign_pointer(resv->fence, new);
but you'll probably want a local ack for amdgpu/
-Chris
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