Re: [PATCH 2/2] drm/amdgpu: use DRM_SCHED_FENCE_DONT_PIPELINE for VM updates

[Luben Tuikov <luben.tuikov@amd.com>]

Hi Christian,

On 2022-10-14 04:15, Christian König wrote:
> Make sure that we always have a CPU round trip to let the submission
> code correctly decide if a TLB flush is necessary or not.
> 
> Signed-off-by: Christian König <christian.koenig@amd.com>
> CC: stable@vger.kernel.org # 5.19+
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_vm_sdma.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_sdma.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_sdma.c
> index 2b0669c464f6..69e105fa41f6 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_sdma.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm_sdma.c
> @@ -116,8 +116,15 @@ static int amdgpu_vm_sdma_commit(struct amdgpu_vm_update_params *p,
>  				   DMA_RESV_USAGE_BOOKKEEP);
>  	}
>  
> -	if (fence && !p->immediate)
> +	if (fence && !p->immediate) {
> +		/*
> +		 * Most hw generations now have a separate queue for page table
> +		 * updates, but when the queue is shared with userspace we need
> +		 * the extra CPU round trip to correctly flush the TLB.
> +		 */
> +		set_bit(DRM_SCHED_FENCE_DONT_PIPELINE, &f->flags);
>  		swap(*fence, f);
> +	}

Do you ever turn that bit off?

Regards
Luben

>  	dma_fence_put(f);
>  	return 0;
>