OpenCL doesn't use full power of the gpu?

I have an AMD 6490m gpu. On the specification it says that its frequency is 700 mhz, but when I obtain the max clock frequency parameter from the opencl api I get 150 mhz. Does anyone know what is the problem?

my platform:
Apple Apple OpenCL 1.2 (Sep 20 2014 22:01:02), FULL_PROFILE

CL_DEVICE_NAME = ATI Radeon HD 6490M
CL_DEVICE_VENDOR = AMD
CL_DEVICE_VERSION = OpenCL 1.2
CL_DRIVER_VERSION = 1.2 (Sep 28 2014 22:27:20)
CL_DEVICE_MAX_COMPUTE_UNITS = 2
CL_DEVICE_MAX_WORK_ITEM_DIMENSIONS = 3
CL_DEVICE_MAX_WORK_ITEM_SIZES = 256 / 256 / 256
CL_DEVICE_MAX_WORK_GROUP_SIZE = 256
CL_DEVICE_MAX_CLOCK_FREQUENCY = 150 MHz
CL_DEVICE_GLOBAL_MEM_SIZE = 256 MB
CL_DEVICE_ERROR_CORRECTION_SUPPORT = NO
CL_DEVICE_LOCAL_MEM_SIZE = 32 kB
CL_DEVICE_MAX_CONSTANT_BUFFER_SIZE = 64 kB

It turned out that AMD implementation returns the value of max clock frequency based on the kind of work the gpu does. If it is or was under heavy work it returns the correct value, otherwise returns the 150 mhz.