commit 4ae315b0d11882f341c22147672e1661bcb3b7d7
author David Turner <david.turner.dev@gmail.com> Thu Mar 05 10:34:25 2020 +0000
committer Commit Bot service account <commit-bot@chromium.org> Thu Mar 05 10:34:25 2020 +0000
tree f288a4414fece0f0fa7c8416dbf9ec3bfbba6164
parent 2de34c1791f301f8ec647afd9011dd3afd502465

Vulkan: Report and enable subgroup size control device extension.

Certain Vulkan ICDs (Intel ones notably) will compile SPIR-V
shaders with an liberal, compiler-selected, subgroup size (i.e.
either 8, 16 or 32). For more context, see [1].

This can be a problem for compute, when one shader stores data
in device memory using a subgroup-size dependent layout, to be
consumed by a another shader. Problems arise when the compiler
decides to compile both shaders with different subgroup sizes.

To work-around this, the VK_EXT_subgroup_size_control device
extension was introduced recently: it allows the device to
report the min/max subgroup sizes it provides, and allows
the Vulkan program to control the subgroup size precisely
if it wants to.

This patch adds support to the Vulkan backend to report and
enable the extension if it is available. Note that:

- The corresponding VkStructureType enum values and
  struct types are not rolled to the third-party Vulkan
  headers used by Dawn yet, so vulkan_platform.h has been
  modified to define them if necessary. This can be
  removed in the future when the Vulkan-Headers are
  updated in a different patch.

- This modifies VulkanDeviceInfo::GatherDeviceInfo() to
  use VkGetPhysicalDevice{Properties2,Features2} if the
  VK_KHR_get_device_properties2 instance extension is
  available. Otherwise, the Vulkan 1.0 APIs
  VkGetPhysicalDevice{Properties,Features} are used instead
  (and it is assumed that no subgroup size control is
  possible).

- This changes the definition of VulkanDeviceKnobs to
  make room for the required pNext-linked chains of
  extensions.

- A helper class, PNextChainBuilder is also provided in
  UtilsVulkan.h to make it easy to build pNext-linked
  extension struct chains at runtime, as required when
  probing device propertires/features, or when
  creating a new VkDevice handle.

Apart from that, there is no change in behaviour in this CL.
I.e. a later CL might force a specific subgroup size for
consistency, or introduce a new API to let Dawn clients
select a fixed subgroup size.

[1] https://bugs.freedesktop.org/show_bug.cgi?id=108875

Change-Id: I524af6ff3479f25b0a8bb139a062fe632c826893
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/16020
Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>