This program displays the count of actual CPU core cycles executed by the current core (using the related PMC which I believe is UNHALTED_CORE_CYCLES)
#include <unistd.h>
#include <cstdio>
int main(int argc, char* argv[]){
unsigned long a, d, c, result;
c = (1UL<<30)+1;
__asm__ volatile("rdpmc" : "=a" (a), "=d" (d) : "c" (c));
result = (a | (d << 32));
printf("Current cycles : %lu\n", result);
}
It works well on Intel processors, but displays a "Segmentation fault" on AMD ones (7001 and 7002). My first guess was to find a new c value related to CPU_CLOCKS_UNHALTED AMD event (0x76) without success for the moment
- I didn't do anything special on the Intel side. Does this PMC is enabled by default?
- How can I make it work on AMD?
- I tried to enable the counter with the wrmsr commands listed here but they also gave me a "Segmentation fault" right away
- I tried the following command
echo 2 | sudo tee /sys/devices/cpu/rdpmc # enable RDPMC always, not just when a perf event is open
