The
profil() function enables or disables program counter profiling of the current process. If profiling is enabled, then at every clock tick, the kernel updates an appropriate count in the
samples buffer.
The buffer
samples contains
size bytes and is divided into a series of 16-bit bins. Each bin counts the number of times the program counter was in a particular address range in the process when a clock tick occurred while profiling was enabled. For a given program counter address, the number of the corresponding bin is given by the relation:
[(pc - offset) / 2] * scale / 65536
The
offset parameter is the lowest address at which the kernel takes program counter samples. The
scale parameter ranges from 1 to 65536 and can be used to change the span of the bins. A scale of 65536 maps each bin to 2 bytes of address range; a scale of 32768 gives 4 bytes, 16384 gives 8 bytes and so on. Intermediate values provide approximate intermediate ranges. A
scale value of 0 disables profiling.