[Mesa-dev] [PATCH v2 2/9] anv: Submit a dummy batch when only semaphores are provided.

[Chris Wilson]

Quoting Jason Ekstrand (2017-08-04 02:25:21)
> Vulkan allows you to do a submit whose only job is to wait on and
> trigger semaphores.  The easiest way for us to support that right
> now is to insert a dummy execbuf.
> ---
> diff --git a/src/intel/vulkan/anv_device.c b/src/intel/vulkan/anv_device.c
> index 793e519..0f0aa22 100644
> --- a/src/intel/vulkan/anv_device.c
> +++ b/src/intel/vulkan/anv_device.c
> @@ -1014,6 +1014,28 @@ anv_device_init_border_colors(struct anv_device *device)
>                                                      border_colors);
>  }
>  
> +static void
> +anv_device_init_trivial_batch(struct anv_device *device)
> +{
> +   anv_bo_init_new(&device->trivial_batch_bo, device, 4096);

Is this created with ASYNC? Just thinking that you only want the
external ordering constraints on this bo, and not accidentally serialize
between contexts.

> +   void *map = anv_gem_mmap(device, device->trivial_batch_bo.gem_handle,
> +                            0, 4096, 0);
> +
> +   struct anv_batch batch = {
> +      .start = map,
> +      .next = map,
> +      .end = map + 4096,
> +   };
> +
> +   anv_batch_emit(&batch, GEN7_MI_BATCH_BUFFER_END, bbe);
> +   anv_batch_emit(&batch, GEN7_MI_NOOP, noop);
> +
> +   if (!device->info.has_llc)
> +      gen_clflush_range(map, batch.next - map);
> +
> +   anv_gem_munmap(map, device->trivial_batch_bo.size);
> +}

> diff --git a/src/intel/vulkan/anv_private.h b/src/intel/vulkan/anv_private.h
> index b599db3..bc67bb6 100644
> --- a/src/intel/vulkan/anv_private.h
> +++ b/src/intel/vulkan/anv_private.h
> @@ -745,6 +745,7 @@ struct anv_device {
>      struct anv_state_pool                       surface_state_pool;
>  
>      struct anv_bo                               workaround_bo;
> +    struct anv_bo                               trivial_batch_bo;

Do you use all 4096 bytes of the workaround_bo, or could you spare 64?
;)

> diff --git a/src/intel/vulkan/anv_queue.c b/src/intel/vulkan/anv_queue.c
> index 446c3de..9934fef 100644
> --- a/src/intel/vulkan/anv_queue.c
> +++ b/src/intel/vulkan/anv_queue.c
> @@ -159,6 +159,23 @@ VkResult anv_QueueSubmit(
>     pthread_mutex_lock(&device->mutex);
>  
>     for (uint32_t i = 0; i < submitCount; i++) {
> +      if (pSubmits[i].commandBufferCount == 0) {
> +         /* If we don't have any command buffers, we need to submit a dummy
> +          * batch to give GEM something to wait on.  We could, potentially,
> +          * come up with something more efficient but this shouldn't be a
> +          * common case.
> +          */
> +         result = anv_cmd_buffer_execbuf(device, NULL,
> +                                         pSubmits[i].pWaitSemaphores,
> +                                         pSubmits[i].waitSemaphoreCount,
> +                                         pSubmits[i].pSignalSemaphores,
> +                                         pSubmits[i].signalSemaphoreCount);

Might as well just pass &pSubmits[i] along?
-Chris