Reading raw perf counter from kernel module

Question

My goal is to read the intel rapl counter ( perf_event_intel_rapl.c ) introduced in kernel 3.14 ( lwn-link ) from within another kernel module. Reading "general" counters is easy using perf_event_create_kernel_counter . I have found an excellent example for that: http://wadeatwork.com/?p=1SW_CPU_CLOCK

The perf manpage ( link ) says, for "non-generalized" events PERF_TYPE_RAW should be used as perf_event_attr->type together with an implementation specific config field.

My question is how I should configure the perf_event_attr struct in order to access the rapl counters. I haven't found any documentation on how to achieve this from a kernel module.

Answer 1

The perf_event support for RAPL includes generalized events that are accessible as system wide, requiring root access (sudo).

You should try the command:

sudo perf list

and see if the event power/energy-cores/ is there, if not, either your CPU has no RAPL support or perf_event does not enable the RAPL features on your CPU. If your CPU support RAPL but it's not enabled in perf_event, you can enable it by adding RAPL support for your CPU to perf_event as described in this link .

Once your CPU is supported, you can use the perf tool to do profiling with the command:

sudo perf stat -e power/energy-cores

For further details, this is a guide with steps to sample RAPL events using perf tool that describes the above with detail and provides some code.