[RFC PATCH 2/2] drm/amdgpu: Dummy CS for VM sync of compute VMs

[Christian König]

Am 10.03.23 um 23:16 schrieb Felix Kuehling:
> Use dummy command submissions with a 0-sized IB on a compute VM to flush
> TLBs and signal the fence in SW. This allows applications with user mode
> queues to sync with asynchronous VM updates through the CS API.

Ok that is really hacky. Going to sync up with Shashank if we can 
implement the TLB flush fence a bit earlier.

Christian.

>
> Signed-off-by: Felix Kuehling <Felix.Kuehling at amd.com>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_ib.c | 9 +++++++++
>   1 file changed, 9 insertions(+)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ib.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ib.c
> index bcccc348dbe2..3f35d04bd4f7 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ib.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ib.c
> @@ -171,6 +171,15 @@ int amdgpu_ib_schedule(struct amdgpu_ring *ring, unsigned num_ibs,
>   		return -EINVAL;
>   	}
>   
> +	if (ib->length_dw == 0 && vm->is_compute_context) {
> +		/* Hack: Dummy CS. Just flush TLBs and signal the fence. */
> +		r = amdgpu_amdkfd_flush_tlb(adev, vm, TLB_FLUSH_LEGACY);
> +		if (r)
> +			return r;
> +		*f = &job->hw_fence;
> +		return dma_fence_signal(*f);
> +	}
> +
>   	alloc_size = ring->funcs->emit_frame_size + num_ibs *
>   		ring->funcs->emit_ib_size;
>