CODEWITHSUNDEEP
vulkan
CoderInHome
CoderInHome

Reputation: 15

vulkan compute shader direct access to CPU allocated memory

Is there any way in vulkan computer shader to bind specific location in CPU memory, So that I can directly access it in shader language.

For example, if I have a variable declaration int a[]={contents........};, can I bind the address of a to say binding location 0 and then access in glsl something like this

layout(std430,binding = 0) {
int a[];
}

I want do this because to I don't want spend time on writing and reading from buffer.

Upvotes: 1

Views: 1268

Answers (2)

krOoze
krOoze

Reputation: 13246

I want do this because to I don't want spend time on writing and reading from buffer.

Vulkan is exactly for people that do want to spend time managing how the data flows. You might want to consider some rapid prototyping framework or math library instead.

Is there any way in vulkan computer shader to bind specific location in CPU memory

Yes, but it won't save you any time.

Firstly Vulkan does allow allocation of CPU memory via VK_MEMORY_PROPERTY_HOST_VISIBLE_BIT|VK_MEMORY_PROPERTY_HOST_COHERENT_BIT. So you could allocate your stuff in that VkDeviceMemory, map it, do your CPU stuff in that address space, and then use it on GPU.

Second way is via using the VK_EXT_external_memory_host extension, which allows you to import your pointer into Vulkan as VK_EXTERNAL_MEMORY_HANDLE_TYPE_HOST_ALLOCATION_BIT_EXT. But it is involved in its own way, and the driver might say "nope", so you are back to square one.

Upvotes: 0

Nicol Bolas
Nicol Bolas

Reputation: 473302

Generally, you cannot make the GPU access memory that Vulkan did not allocate itself for the GPU. The exception to this are external allocations made by other APIs that themselves are allocating GPU-accessible memory.

Just taking a random stack or global pointer and shoving it at Vulkan isn't going to work.

I want something like cudaHostGetDevicePointer in CUDA

What you're asking for here is not what that function does. That function takes a CPU pointer to CPU-accessible memory which CUDA allocated for you and which you previously mapped into a CPU address range. The pointer you give it must be within a mapped region of GPU memory.

You can't just shove a stack/global variable at it and expect it to work. The variable would have to be within the mapped allocation, and a global or stack variable can't be within such an allocation.

Vulkan doesn't have a way to reverse-engineer a pointer into a mapped range of device memory back to the VkDeviceMemory object it was mapped from. This is in part because Vulkan doesn't have pointers to allocations; you have to use VkDeviceMemory object, which you create and manage yourself. But if you need to know where a CPU-accessible pointer was mapped from, you can keep track of that yourself.

Upvotes: 2

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