tree 940030b29e2c776dc7ce5d6abdc0aebea95f158d
parent 984493d0ac077cccbe4e5b83ab6028aaa5d40357
author Corentin Wallez <cwallez@chromium.org> 1592294068 +0000
committer Commit Bot service account <commit-bot@chromium.org> 1592294068 +0000

Reland: Vulkan: Report and enable subgroup size control device extension.

Reland after a refactor of how the extension handling work in the Vulkan
backend.

The original author is David Turner <david.turner.dev@gmail.com>.

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:

- 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.

- This modifies VulkanDeviceInfo::GatherDeviceInfo() to
  use PNextChainBuilder to query extension features and properties
  in a single call to vkGetPhysicalDevice{Properties,Features}2.

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

Bug: dawn:464
Change-Id: I01e5c28e7dac66f0a57bf35532eb192912b254fa
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/23201
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>