[Mesa-dev] [PATCH] radv: Change memory type order for GPUs without dedicated VRAM

[Bas Nieuwenhuizen]

On Sun, Jun 2, 2019 at 12:32 PM Alex Smith <asmith at feralinteractive.com> wrote:
>
> Put the uncached GTT type at a higher index than the visible VRAM type,
> rather than having GTT first.
>
> When we don't have dedicated VRAM, we don't have a non-visible VRAM
> type, and the property flags for GTT and visible VRAM are identical.
> According to the spec, for types with identical flags, we should give
> the one with better performance a lower index.
>
> Previously, apps which follow the spec guidance for choosing a memory
> type would have picked the GTT type in preference to visible VRAM (all
> Feral games will do this), and end up with lower performance.
>
> On a Ryzen 5 2500U laptop (Raven Ridge), this improves average FPS in
> the Rise of the Tomb Raider benchmark by up to ~30%. Tested a couple of
> other (Feral) games and saw similar improvement on those as well.
>
> Signed-off-by: Alex Smith <asmith at feralinteractive.com>
> ---
> I noticed that the memory types advertised on my Raven laptop looked a
> bit odd so played around with it and found this. I'm not sure if it is
> actually expected that the performance difference between visible VRAM
> and GTT is so large, seeing as it's not dedicated VRAM, but the results
> are clear (and consistent, tested multiple times).

AFAIU it is still using different memory paths, with GTT using
different pagetables (those from the CPU I believe on APUs) and
possible CPU snooping.

Main risk here seems applications pushing out driver internal stuff
(descriptor sets etc.) from "VRAM", posssibly hitting perf elsewhere.
That said,

Reviewed-by: Bas Nieuwenhuizen <bas at basnieuwenhuizen.nl>

> ---
>  src/amd/vulkan/radv_device.c | 18 +++++++++++++++---
>  1 file changed, 15 insertions(+), 3 deletions(-)
>
> diff --git a/src/amd/vulkan/radv_device.c b/src/amd/vulkan/radv_device.c
> index 3cf050ed220..d36ee226ebd 100644
> --- a/src/amd/vulkan/radv_device.c
> +++ b/src/amd/vulkan/radv_device.c
> @@ -171,12 +171,11 @@ radv_physical_device_init_mem_types(struct radv_physical_device *device)
>                         .heapIndex = vram_index,
>                 };
>         }
> -       if (gart_index >= 0) {
> +       if (gart_index >= 0 && device->rad_info.has_dedicated_vram) {
>                 device->mem_type_indices[type_count] = RADV_MEM_TYPE_GTT_WRITE_COMBINE;
>                 device->memory_properties.memoryTypes[type_count++] = (VkMemoryType) {
>                         .propertyFlags = VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT |
> -                       VK_MEMORY_PROPERTY_HOST_COHERENT_BIT |
> -                       (device->rad_info.has_dedicated_vram ? 0 : VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT),
> +                       VK_MEMORY_PROPERTY_HOST_COHERENT_BIT,
>                         .heapIndex = gart_index,
>                 };
>         }
> @@ -189,6 +188,19 @@ radv_physical_device_init_mem_types(struct radv_physical_device *device)
>                         .heapIndex = visible_vram_index,
>                 };
>         }
> +       if (gart_index >= 0 && !device->rad_info.has_dedicated_vram) {
> +               /* Put GTT after visible VRAM for GPUs without dedicated VRAM
> +                * as they have identical property flags, and according to the
> +                * spec, for types with identical flags, the one with greater
> +                * performance must be given a lower index. */
> +               device->mem_type_indices[type_count] = RADV_MEM_TYPE_GTT_WRITE_COMBINE;
> +               device->memory_properties.memoryTypes[type_count++] = (VkMemoryType) {
> +                       .propertyFlags = VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT |
> +                       VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT |
> +                       VK_MEMORY_PROPERTY_HOST_COHERENT_BIT,
> +                       .heapIndex = gart_index,
> +               };
> +       }
>         if (gart_index >= 0) {
>                 device->mem_type_indices[type_count] = RADV_MEM_TYPE_GTT_CACHED;
>                 device->memory_properties.memoryTypes[type_count++] = (VkMemoryType) {
> --
> 2.21.0
>
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