[Mesa-dev] [PATCH vulkan/spec 1/3] Add an extension to specify that derivative groups are quads
Jason Ekstrand
jason at jlekstrand.net
Wed Nov 7 03:52:58 UTC 2018
On Tue, Nov 6, 2018 at 9:43 PM Roland Scheidegger <sroland at vmware.com>
wrote:
> Am 06.11.18 um 22:48 schrieb Jason Ekstrand:
> > This came to the top of my list recently due to a difference between
> > OpenGL and Vulkan discard operations and D3D's discard operation. The
> > OpenGL and Vulkan discard is defined to be control flow and derivatives
> > are undefined after discard. With D3D, derivatives are considered
> > well-defined after discard.
> >
> > In order to work around this, DXVK (and I would assume VKD3D though I'm
> > not sure), simply sets a global boolean instead of doing the discard and
> > then emits `if (do_discard) discard;` at the end of the shader. For
> > complex shadaers, this leads to the shader doing way more work than
> > needed and poor performance.
> Is that really all they do? This will not work in presence of UAVs
> (shader images / ssbos), since after a discard writes must have no effect.
>
I'm not sure off-hand how UAVs are handled in the presence of discards. I
would guess something like if (!discard) writeUAV();
> > If, on the other hand, they knew that
> > derivative groups are just subgroup quads, they could do something
> > better:
> >
> > bool want_discard;
> >
> > void d3d_discard()
> > {
> > want_discard = true;
> > if (subgroupClusteredAnd(want_discard, 4))
> > discard;
> > }
> >
> > void main()
> > {
> > want_discard = false;
> >
> > // stuff
> >
> > if (some_condition)
> > d3d_discard();
> >
> > // Exepensive stuff
> Expensive
>
> >
> > if (want_discard)
> > discard;
> If the expensive stuff includes buffer / image writes, that still
> wouldn't work as far as I can tell (although it could be fixed, just
> like without the extension, by wrapping the writes with if (!want_discard).
>
Correct. However, the common case is UBO pulls and textures.
--Jason
> Roland
>
>
> > }
> > ---
> > chapters/features.txt | 21 +++++++++++++++++++++
> > chapters/shaders.txt | 12 ++++++++++++
> > chapters/textures.txt | 8 ++++++++
> > include/vulkan/vulkan_core.h | 15 +++++++++++++--
> > xml/vk.xml | 13 ++++++++++---
> > 5 files changed, 64 insertions(+), 5 deletions(-)
> >
> > diff --git a/chapters/features.txt b/chapters/features.txt
> > index 08c8d8420..3d22972ea 100644
> > --- a/chapters/features.txt
> > +++ b/chapters/features.txt
> > @@ -2969,6 +2969,27 @@ more slink:VkSubgroupFeatureFlagBits.
> >
> > endif::VK_VERSION_1_1[]
> >
> > +ifdef::VK_EXT_derivative_group_quad[]
> > +
> >
> +[open,refpage='VkPhysicalDeviceDerivativeGroupQuadPropertiesEXT',desc='Structure
> describing the relationship between derivative groups and subgroup quads
> for an implementation',type='structs']
> > +--
> > +
> > +The sname:VkPhysicalDeviceDerivativeGroupQuadPropertiesEXT structure is
> > +defined as:
> > +
> >
> +include::../api/structs/VkPhysicalDeviceDerivativeGroupQuadPropertiesEXT.txt[]
> > +
> > +The members of the
> sname:VkPhysicalDeviceDerivativeGroupQuadPropertiesEXT
> > +structure describe the following implementation-dependent limits:
> > +
> > + * pname:derivativeGroupsAreSubgroupQuads is a boolean that specifies
> that
> > + derivative groups in fragment shaders correspond to subgroup quads.
> > +--
> > +
> >
> +include::../validity/structs/VkPhysicalDeviceDerivativeGroupQuadPropertiesEXT.txt[]
> > +
> > +endif::VK_EXT_derivative_group_quad[]
> > +
> > ifdef::VK_EXT_blend_operation_advanced[]
> >
> >
> [open,refpage='VkPhysicalDeviceBlendOperationAdvancedPropertiesEXT',desc='Structure
> describing advanced blending limits that can be supported by an
> implementation',type='structs']
> > diff --git a/chapters/shaders.txt b/chapters/shaders.txt
> > index 5cb3edb35..11d3ea9db 100644
> > --- a/chapters/shaders.txt
> > +++ b/chapters/shaders.txt
> > @@ -808,6 +808,11 @@ A _derivative group_ (see the subsection "`Control
> Flow`" of section 2 of
> > the SPIR-V 1.00 Revision 4 specification) for a fragment shader is the
> set
> > of invocations generated by a single primitive (point, line, or
> triangle),
> > including any helper invocations generated by that primitive.
> > +ifdef::VK_EXT_derivative_group_quad[]
> > +If the fname:derivativeGroupsAreSubgroupQuads field of
> > +slink:VkPhysicalDeviceDerivativeGroupQuadPropertiesEXT is
> ename:VK_TRUE, a
> > +derivative group for a fragment shader is a single subgroup quad.
> > +endif::VK_EXT_derivative_group_quad[]
> > ifdef::VK_NV_compute_shader_derivatives[]
> > A derivative group for a compute shader is a single local workgroup.
> > endif::VK_NV_compute_shader_derivatives[]
> > @@ -920,6 +925,13 @@ The operations supported are add, mul, min, max,
> and, or, xor.
> >
> > The quad subgroup operations allow clusters of 4 invocations (a quad),
> to
> > share data efficiently with each other.
> > +ifdef::VK_EXT_derivative_group_quad[]
> > +For fragment shaders, if the fname:derivativeGroupsAreSubgroupQuads
> field of
> > +slink:VkPhysicalDeviceDerivativeGroupQuadPropertiesEXT is ename:VK_TRUE,
> > +each quad corresponds to one of the groups of four shader
> > +invocations used for
> > +<<texture-derivatives-compute,derivatives>>.
> > +endif::VK_EXT_derivative_group_quad[]
> > ifdef::VK_NV_compute_shader_derivatives[]
> > For compute shaders using the code:DerivativeGroupQuadsNV or
> > code:DerivativeGroupLinearNV execution modes, each quad corresponds to
> one
> > diff --git a/chapters/textures.txt b/chapters/textures.txt
> > index a7bfaedc3..46a292381 100644
> > --- a/chapters/textures.txt
> > +++ b/chapters/textures.txt
> > @@ -1387,6 +1387,14 @@ Implementations must: make the same choice of
> either coarse or fine for both
> > code:OpDPdx and code:OpDPdy, and implementations should: make the choice
> > that is more efficient to compute.
> >
> > +ifdef::VK_EXT_derivative_group_quad[]
> > +If the fname:derivativeGroupsAreSubgroupQuads field of
> > +slink:VkPhysicalDeviceDerivativeGroupQuadPropertiesEXT is ename:VK_TRUE,
> > +the 2x2 neighborhood of fragments corresponds exactly to a subgroup quad
> > +the invocations in each quad are ordered to have attribute values of
> > +P~i0,j0~, P~i1,j0~, P~i0,j1~, and P~i1,j1~, respectively.
> > +endif::VK_EXT_derivative_group_quad[]
> > +
> > ifdef::VK_NV_compute_shader_derivatives[]
> > [[texture-derivatives-compute]]
> > === Compute Shader Derivatives
> > diff --git a/include/vulkan/vulkan_core.h b/include/vulkan/vulkan_core.h
> > index 4cd8ed51d..7b304eafe 100644
> > --- a/include/vulkan/vulkan_core.h
> > +++ b/include/vulkan/vulkan_core.h
> > @@ -451,6 +451,7 @@ typedef enum VkStructureType {
> > VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_EXCLUSIVE_SCISSOR_FEATURES_NV =
> 1000205002,
> > VK_STRUCTURE_TYPE_CHECKPOINT_DATA_NV = 1000206000,
> > VK_STRUCTURE_TYPE_QUEUE_FAMILY_CHECKPOINT_PROPERTIES_NV =
> 1000206001,
> > +
> VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_DERIVATIVE_GROUP_QUAD_PROPERTIES_EXT =
> 1000209000,
> > VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_VULKAN_MEMORY_MODEL_FEATURES_KHR
> = 1000211000,
> > VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_PCI_BUS_INFO_PROPERTIES_EXT =
> 1000212000,
> > VK_STRUCTURE_TYPE_IMAGEPIPE_SURFACE_CREATE_INFO_FUCHSIA =
> 1000214000,
> > @@ -7791,8 +7792,6 @@ typedef struct
> VkPipelineCoverageModulationStateCreateInfoNV {
> >
> >
> > #define VK_EXT_image_drm_format_modifier 1
> > -#define VK_EXT_EXTENSION_159_SPEC_VERSION 0
> > -#define VK_EXT_EXTENSION_159_EXTENSION_NAME "VK_EXT_extension_159"
> > #define VK_EXT_IMAGE_DRM_FORMAT_MODIFIER_SPEC_VERSION 1
> > #define VK_EXT_IMAGE_DRM_FORMAT_MODIFIER_EXTENSION_NAME
> "VK_EXT_image_drm_format_modifier"
> >
> > @@ -8791,6 +8790,18 @@ VKAPI_ATTR void VKAPI_CALL
> vkGetQueueCheckpointDataNV(
> > VkCheckpointDataNV* pCheckpointData);
> > #endif
> >
> > +#define VK_EXT_derivative_group_quad 1
> > +#define VK_EXT_DERIVATIVE_GROUP_QUAD_SPEC_VERSION 1
> > +#define VK_EXT_DERIVATIVE_GROUP_QUAD_EXTENSION_NAME
> "VK_EXT_derivative_group_quad"
> > +
> > +typedef struct VkPhysicalDeviceDerivativeGroupQuadPropertiesEXT {
> > + VkStructureType sType;
> > + const void* pNext;
> > + VkBool32 derivativeGroupsAreSubgroupQuads;
> > +} VkPhysicalDeviceDerivativeGroupQuadPropertiesEXT;
> > +
> > +
> > +
> > #define VK_EXT_pci_bus_info 1
> > #define VK_EXT_PCI_BUS_INFO_SPEC_VERSION 1
> > #define VK_EXT_PCI_BUS_INFO_EXTENSION_NAME "VK_EXT_pci_bus_info"
> > diff --git a/xml/vk.xml b/xml/vk.xml
> > index 24cc3ce78..93dc66159 100644
> > --- a/xml/vk.xml
> > +++ b/xml/vk.xml
> > @@ -3590,6 +3590,11 @@ server.
> > <member>const <type>void</type>*
> <name>pNext</name></member>
> > <member><type>VkMemoryOverallocationBehaviorAMD</type>
> <name>overallocationBehavior</name></member>
> > </type>
> > + <type category="struct"
> name="VkPhysicalDeviceDerivativeGroupQuadPropertiesEXT"
> structextends="VkPhysicalDeviceProperties2">
> > + <member
> values="VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_DERIVATIVE_GROUP_QUAD_PROPERTIES_EXT"><type>VkStructureType</type>
> <name>sType</name></member>
> > + <member>const <type>void</type>*
> <name>pNext</name></member>
> > + <member><type>VkBool32</type>
> <name>derivativeGroupsAreSubgroupQuads</name></member>
> > + </type>
> > </types>
> >
> > <comment>Vulkan enumerant (token) definitions</comment>
> > @@ -9893,10 +9898,12 @@ server.
> > <enum value=""VK_KHR_extension_209""
> name="VK_KHR_EXTENSION_209_EXTENSION_NAME"/>
> > </require>
> > </extension>
> > - <extension name="VK_INTEL_extension_210" number="210"
> type="device" author="INTEL" contact="Jason Ekstrand @jekstrand"
> supported="disabled">
> > + <extension name="VK_EXT_derivative_group_quad" number="210"
> type="device" requiresCore="1.1" author="EXT" contact="Jason Ekstrand
> @jekstrand" supported="vulkan">
> > <require>
> > - <enum value="0"
> name="VK_KHR_EXTENSION_210_SPEC_VERSION"/>
> > - <enum value=""VK_KHR_extension_210""
> name="VK_KHR_EXTENSION_210_EXTENSION_NAME"/>
> > + <enum value="1"
> name="VK_EXT_DERIVATIVE_GROUP_QUAD_SPEC_VERSION"/>
> > + <enum value=""VK_EXT_derivative_group_quad""
> name="VK_EXT_DERIVATIVE_GROUP_QUAD_EXTENSION_NAME"/>
> > + <enum offset="0" extends="VkStructureType"
> name="VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_DERIVATIVE_GROUP_QUAD_PROPERTIES_EXT"/>
> > + <type
> name="VkPhysicalDeviceDerivativeGroupQuadPropertiesEXT"/>
> > </require>
> > </extension>
> > <extension name="VK_INTEL_extension_211" number="211"
> type="device" author="INTEL" contact="Jason Ekstrand @jekstrand"
> supported="disabled">
> >
>
>
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