Is it possible to achieve the same level of parallelism with a multiple core CPU device as that of multiple heterogenous devices ( like GPU and CPU ) in OpenCL?
I have an intel i5 and am looking to optimise my code. When I query the platform for devices I get only one device returned: the CPU. I was wondering how I could optimise my code by using this.
Also, if I used a single command queue for this device, would the application automatically assign the kernels to different compute devices or does it have to be done manually by the programmer?
Short answer: yes, it will run in parallel and no, no need to do it manually.
Long answer:
Either you need to revise your OpenCL vocabulary or I didn’t understand your question. You only have one device and core != device!
One CPU, regardless of how many cores it has, is one device. The same goes for a GPU: one GPU, which has hundreds of cores, is only one device. You send jobs to the device through the queue and the device’s driver. Your jobs can (and will) be split up into work-items. Then, some (how many depends on the device/driver) work-items are executed in parallel. On the GPU aswell as on the CPU, one work-item is executed by one kernel. (This might not be completely true but it is a very helpful abstraction.)
If you enqueue several kernels in one queue (without connecting them through a wait event!), the driver may or may not run them in parallel.
It is the very goal of OpenCL to allow you to compute work-items in parallel regardless of whether it is using several devices’ cores in parallel or only a single devices cores.
If this confuses you, watch these really good (and long) videos: http://macresearch.org/opencl