About the support for the instruction RDPMC

[U1tra1isk]

I am wonderring whether the RDPMC instrcution is supported in recent generations of CPU. My CPU is i9-10980XE and I use Debian 12.6. I run a test program using the cpuid instruction and find that the RDPMC is not supported. The test code given by ChatGPT is shown below

#include <stdio.h>
#include <cpuid.h>

void check_rdpmc_support() {
    unsigned int eax, ebx, ecx, edx;
    __cpuid(0xA, eax, ebx, ecx, edx);
    if (edx & (1 << 23)) {
        printf("RDPMC is supported\n");
    } else {
        printf("RDPMC is not supported\n");
    }
}

int main() {
    check_rdpmc_support();
    return 0;
}

It turns out to be not supported.

The most primitive problem is that I want to monitoring the performance of a circle. I tried RDMSR instruction at first, but as RDMSR needs privilege 0 and the cost of using system call is unaffordable. Also, system call also introduce unpredictable extra cost itself. This also happens on the Perf, so I turn to RDPMC. As ChatGpt says, it can be used on privilege 3, but I have never make it successfully. The test program above also indicates the RDPMC is not supported in my machine. So I am wondering whether it can be used at privilege 3. If we can use it at privilege 3, then which CPU support it in recent generations (10-14 generation)?

[edwarddavidbaker]

Thanks for opening an issue. For a RDPMC reference please review https://github.com/andikleen/pmu-tools/blob/master/jevents/rdpmc.c . Depending on your Linux distribution you may also need to set /sys/devices/cpu/rdpmc to allow user space access. The RDPMC instruction is still available on recent generations.