How to get the max memory allocation size for a single buffer?

jjfumero commented 2 years ago

I am allocating some large buffers with zeMemAllocShared, zeMemAllocDevice and zeMemAllocHost functions from Level Zero. I am able to allocate ~4.9GB on my system, despite the fact that, with my configuration, OpenCL max allocation is set to 4 GiB for the same Intel HD graphics.

  Address bits                                    64, Little-Endian
  Global memory size                              26706980864 (24.87GiB)
  Error Correction support                        No
  Max memory allocation                           4294959104 (4GiB)

Is there any way in Level Zero to obtain the max allocation size for a single buffer? I was looking at this struct, but I can't find such information: https://spec.oneapi.io/level-zero/latest/core/api.html?highlight=device_memory_properties#_CPPv429ze_device_memory_properties_t

Also, is there any way to allocate more than 5GB for a single buffer?

bmyates commented 2 years ago

I think maxMemAllocSize in ze_device_properties_t is what you are looking for.

There is also an extension that will let you allocate beyond that limit. See ze_relaxed_allocation_limits_exp_desc_t

jjfumero commented 2 years ago

Thank you @bmyates. That's exactly what I was looking for.

jjfumero commented 2 years ago

Interesting. This seems to work. I am able to allocate 8GB.

./levelZeroAlloc 8147483648
Device   : Intel(R) UHD Graphics [0x9bc4]
Type     : GPU
Vendor ID: 8086

Allocating Shared: 8147483648 bytes - 8.14748 (GB)  ----- [OK]

Just for reference, this works (e.g,, a shared memory buffer):

ze_device_mem_alloc_desc_t memAllocDesc = {ZE_STRUCTURE_TYPE_DEVICE_MEM_ALLOC_DESC};
memAllocDesc.flags = ZE_DEVICE_MEM_ALLOC_FLAG_BIAS_CACHED;
memAllocDesc.ordinal = 0;

ze_host_mem_alloc_desc_t hostDesc = {ZE_STRUCTURE_TYPE_HOST_MEM_ALLOC_DESC};

ze_relaxed_allocation_limits_exp_desc_t exceedCapacity = {
        ZE_STRUCTURE_TYPE_RELAXED_ALLOCATION_LIMITS_EXP_DESC,
        nullptr, 
        ZE_RELAXED_ALLOCATION_LIMITS_EXP_FLAG_MAX_SIZE
    };

void *sharedBuffer = nullptr;

hostDesc.pNext = &exceedCapacity;
memAllocDesc.pNext = &exceedCapacity;

result = zeMemAllocShared(context, &memAllocDesc, &hostDesc, allocSize, 128, device, &sharedBuffer);

A follow-up question is from the comment in the SPEC:

Allocation size may exceed ze_device_properties_t.maxMemAllocSize.

https://github.com/oneapi-src/level-zero/blob/master/include/ze_api.h#L6312

Does this mean that the requested extended size is not guaranteed?

jandres742 commented 2 years ago

@jjfumero this is a question on spec. Please move it to https://github.com/oneapi-src/level-zero-spec/issues

oneapi-src / level-zero

How to get the max memory allocation size for a single buffer? #88