topic >>...Why is the limit set to in OpenCL* for CPU

Allocating large buffers

Luis_Aguilar — Sat, 15 Jun 2013 13:29:16 GMT

Hi,

How can I allocate a single large buffer of 8GB ?

My Core i7 reports

CL_DEVICE_GLOBAL_MEM_SIZE: 16780570624

but

CL_DEVICE_MAX_MEM_ALLOC_SIZE: 4195142656

How can I increase the MAX ALLOC SIZE limit in Intel OpenCL SDK?

Thanks

Sorry it took a while for

Raghupathi_M_Intel — Wed, 21 Aug 2013 18:48:29 GMT

Sorry it took a while for responding. Not sure if you are still looking for an answer. In theory you cannot allocate a buffer whose size is more than CL_DEVICE_MAX_MEM_ALLOC_SIZE (OpenCL doesn't allow that). But if you need a buffer that's larger than CL_DEVICE_MAX_MEM_ALLOC_SIZE, you might have to allocate multiple buffers and implement logic in your code to merge the result from these multiple buffers. What exactly are you trying to do?

Thanks,
Raghu

I know this is an old thread,

joshbowden — Fri, 25 Jul 2014 01:53:49 GMT

I know this is an old thread, however I have the same issue - I cannot allocate buffers that are > 1/4th of my available memory due to someone implementing an artificial limit.

The OpenCL specification does not seem to imply this limit. Please read https://www.khronos.org/registry/cl/specs/opencl-1.2.pdf on page 39 table 4.3 it states:

CL_DEVICE_MAX_MEM_ALLOC_SIZE
cl_ulong
Max size of memory object allocation in bytes. The minimum value is max (1/4th of CL_DEVICE_GLOBAL_MEM_SIZE , 128*1024*1024) for devices that are not of type CL_DEVICE_TYPE_CUSTOM.

Can someone please tell me why Intel OpenCL drivers (v4.4 of July 2014) impose the minimum value and not just let the CL_DEVICE_MAX_MEM_ALLOC_SIZE be set to be as big as the memory available?

Thanks,
Josh

I know this thread is old and

Harald_S_ — Fri, 02 Sep 2016 17:30:56 GMT

I know this thread is old and was unearthed before but this is exactly the question I would like to ask and I did not want to open another thread. Maybe somebody got the answer somewhere in the meantime.

Why is the limit set to 1/4th?

Thank you

Do you need to know just for

Jeffrey_M_Intel1 — Sat, 10 Sep 2016 00:36:29 GMT

Do you need to know just for CPU, or do you need more info about the GPU max alloc size too?

Especially CPU but if you can

Harald_S_ — Wed, 14 Sep 2016 18:44:06 GMT

Especially CPU but if you can tell me about the GPU limitation as well I would appreciate that. :)

>>My Core i7 reports

SergeyKostrov — Thu, 15 Sep 2016 00:29:03 GMT

>>My Core i7 reports >> >>CL_DEVICE_GLOBAL_MEM_SIZE: 16780570624 >> >>but >> >>CL_DEVICE_MAX_MEM_ALLOC_SIZE: 4195142656 I just checked a video card on my Dell Precision Mobile Workstation ( M4700 ) and it looks like the 1/4th-rule is applicable to all devices: ... oclDeviceQuery.exe Starting... OpenCL SW Info: CL_PLATFORM_NAME: NVIDIA CUDA CL_PLATFORM_VERSION: OpenCL 1.2 CUDA 8.0.0 OpenCL SDK Revision: 7027912 OpenCL Device Info: 1 devices found supporting OpenCL: --------------------------------- Device Quadro K1000M --------------------------------- CL_DEVICE_NAME: Quadro K1000M CL_DEVICE_VENDOR: NVIDIA Corporation CL_DRIVER_VERSION: 369.26 CL_DEVICE_VERSION: OpenCL 1.2 CUDA CL_DEVICE_OPENCL_C_VERSION: OpenCL C 1.2 CL_DEVICE_TYPE: CL_DEVICE_TYPE_GPU CL_DEVICE_MAX_COMPUTE_UNITS: 1 CL_DEVICE_MAX_WORK_ITEM_DIMENSIONS: 3 CL_DEVICE_MAX_WORK_ITEM_SIZES: 1024 / 1024 / 64 CL_DEVICE_MAX_WORK_GROUP_SIZE: 1024 CL_DEVICE_MAX_CLOCK_FREQUENCY: 850 MHz CL_DEVICE_ADDRESS_BITS: 64 CL_DEVICE_MAX_MEM_ALLOC_SIZE: 512 MByte CL_DEVICE_GLOBAL_MEM_SIZE: 2048 MByte CL_DEVICE_ERROR_CORRECTION_SUPPORT: no CL_DEVICE_LOCAL_MEM_TYPE: local CL_DEVICE_LOCAL_MEM_SIZE: 48 KByte CL_DEVICE_MAX_CONSTANT_BUFFER_SIZE: 64 KByte CL_DEVICE_QUEUE_PROPERTIES: CL_QUEUE_OUT_OF_ORDER_EXEC_MODE_ENABLE CL_DEVICE_QUEUE_PROPERTIES: CL_QUEUE_PROFILING_ENABLE CL_DEVICE_IMAGE_SUPPORT: 1 CL_DEVICE_MAX_READ_IMAGE_ARGS: 256 CL_DEVICE_MAX_WRITE_IMAGE_ARGS: 16 CL_DEVICE_SINGLE_FP_CONFIG: denorms INF-quietNaNs round-to-nearest round-to-zero round-to-inf fma ...

>>...Why is the limit set to

SergeyKostrov — Thu, 15 Sep 2016 00:41:54 GMT

>>...Why is the limit set to 1/4th? I think this needs to be addressed to somebody from Khronos who is responsible for OpenCL specifications.

I'm not an expert on the

joshbowden — Thu, 15 Sep 2016 01:14:16 GMT

I'm not an expert on the OpenCL specification, however this is what OpenCL 1.2 spec sheet says: "The minimum value is max (1/4th of CL_DEVICE_GLOBAL_MEM_SIZE , 128*1024*1024) "

so, the specification specifies a minimum value. This does not mean the minimum value should be implemented as the maximum value!

There is a 2nd part of the

SergeyKostrov — Thu, 15 Sep 2016 15:12:45 GMT

There is a 2nd part of the statement about "...for devices that are not of type CL_DEVICE_TYPE_CUSTOM..." In case of my Quadro K1000M card this is: ... CL_DEVICE_TYPE: CL_DEVICE_TYPE_GPU ... I wonder if Altera FPGA cards are classified as CL_DEVICE_TYPE_CUSTOM and do Not have that restriction. Could somebody from Intel verify it?