Detect current CPU Clock Speed Programmatically on OS X?

Question

I just bought a nifty MBA 13" Core i7. I'm told the CPU speed varies automatically, and pretty wildly, too. I'd really like to be able to monitor this with a simple app.

Are there any Cocoa or C calls to find the current clock speed, without actually affecting it?

Edit: I'm OK with answers using Terminal calls, as well as programmatic.

Thanks!

Solution 1

Try this tool called "Intel Power Gadget". It displays IA frequency and IA power in real time.

http://software.intel.com/sites/default/files/article/184535/intel-power-gadget-2.zip

Solution 2

You can query the CPU speed easily via sysctl, either by command line:

sysctl hw.cpufrequency

Or via C:

#include <stdio.h>
#include <sys/types.h>
#include <sys/sysctl.h>

int main() {
        int mib[2];
        unsigned int freq;
        size_t len;

        mib[0] = CTL_HW;
        mib[1] = HW_CPU_FREQ;
        len = sizeof(freq);
        sysctl(mib, 2, &freq, &len, NULL, 0);

        printf("%u\n", freq);

        return 0;
}

Solution 3

Since it's an Intel processor, you could always use RDTSC. That's an assembler instruction that returns the current cycle counter — a 64bit counter that increments every cycle. It'd be a little approximate but e.g.

#include <stdio.h>
#include <stdint.h>
#include <unistd.h>

uint64_t rdtsc(void)
{
    uint32_t ret0[2];
    __asm__ __volatile__("rdtsc" : "=a"(ret0[0]), "=d"(ret0[1]));
    return ((uint64_t)ret0[1] << 32) | ret0[0];
}

int main(int argc, const char * argv[])
{
    uint64_t startCount = rdtsc();
    sleep(1);
    uint64_t endCount = rdtsc();

    printf("Clocks per second: %llu", endCount - startCount);

    return 0;
}

Output 'Clocks per second: 2002120630' on my 2Ghz MacBook Pro.

Comments

[Tim]

On my MBA, it shows 1.8ghz, which is exactly right, but is there any way to force the i7 into turbo boost?

[Mysticial]

rdtsc is not a reliable way to measure a processor's clock speed. It does not adjust itself to turbo-boost/CPU-throttling (among other things).

[Tommy]

@Mysticial on the contrary; it's usually advised as being an unreliable way to measure a CPU's clock speed exactly because it is affected by turbo boost and CPU throttling.

[Mysticial]

@Tommy My tests suggests other wise. On my Xeon at stock 3.2 GHz rdtsc always says 3.2 GHz regardless of what I set the multiplier to (2.4, 2.6, 2.8, 3.0, 3.2 GHz... all get reported as 3.2 GHz by rdtsc) rdtsc seems to change only when you start messing with the bus speeds.

[Tim]

Is there a way to determine what the multiplier is? I'm interested in both knowing what speedstep pulls the CPU down to at idle and where TurboBoost puts the CPU under load.

[Mysticial]

@Tim, I think you have to access the BIOS to get bus-speed/multiplier information. There's no easy way to do that since there are hundreds of different motherboard/BIOS/CPU systems...

[Tim]

@Mystical I've seen some apps around which claim to find the information about current core speed, including Intel's own app (on Windows), but no source code anywhere. I'm sure there's a way to do it - Intel has a big ole' pdf with sample code but I can't get it to compile - though I'll continue trying.

[Tim]

Unfortunately, this seems to return the "box advertised" speed (now 2.3ghz on my MBPR) but not the SpeedStep adjusted speed.

[Tim]

However, this is a useful and easy insight into the use of sysctl, so thank you for that!

[Tim]

This is really exactly what I wanted. It even includes sample objective-c... Perfect!

[Tim]

Running sysctl kern.clockrate at command line gives me a steady kern.clockrate: { hz = 100, tick = 10000, tickadj = 2, profhz = 100, stathz = 100 } where the Intel CPU profiler is showing varying values, so I don't think this works with the speedstep adjustments.

[mist]

Does not give current, but advertised speed. hw.cpufrequency, hw.cpufrequency_min, hw.cpufrequency_max all give the same.

[Ken Aspeslagh]

This code will overflow the Hz on the new generation of > 4Ghz processors. Need to use this instead. sysctlbyname("hw.cpufrequency_max", &speed, &len, NULL, 0); to support a 64-bit value for the frequency.

[rogerdpack]

hmm sysctl hw.cpufrequency always reports 2500000000 for me. The Intel Power Gadgetreports varying "IA" values from 1.3Ghz to 3.4GHz, wonder if there's a way to get more up to date values...