Code demonstrating the apparent missed REF_TSC cycles when TurboBoost is enabled, as described on this Stack Overflow question.

Clone, Build and Install Kernel Module

git clone --recursive https://github.com/travisdowns/turbo-cycles-mystery
cd turbo-cycles-mystery
make
sudo insmod libpfc/pfc.ko

Run

make run

This will prompt you for root credentials to install the pfc.ko kernel module, as well as enable userland rdpmc calls. The demo process itself is not run as root. You can inpsect the makefile for details.

Typical Output

TurboBoost OFF

Pinned to CPU 0
CPU# REF_TSC   rdtsc Eff Mhz
   0 2589.52 2591.93 2589.07
   0 2590.80 2591.94 2590.81
   0 2590.38 2591.94 2590.10
   0 2590.80 2591.94 2590.66
   0 2590.57 2591.94 2590.61
   0 2590.70 2591.94 2590.23
   0 2590.66 2591.94 2591.07
   0 2590.33 2591.94 2590.38
   0 2590.24 2591.94 2590.05
   0 2590.83 2591.94 2591.12
   0 2590.63 2591.94 2590.22
   0 2590.56 2591.94 2590.29
   0 2590.88 2591.94 2590.82
   0 2590.35 2591.94 2588.98
   0 2590.71 2591.94 2590.67
   ...

TurboBoost ON

Pinned to CPU 0
CPU# REF_TSC   rdtsc Eff Mhz
   0 2451.80 2591.93 3238.33
   0 2452.46 2591.94 3240.19
   0 2478.53 2591.94 3303.37
   0 2482.48 2591.94 3299.19
   0 2461.07 2591.93 3274.17
   0 2445.60 2591.94 3247.31
   0 2452.25 2591.94 3259.14
   0 2460.98 2591.94 3252.05
   0 2491.09 2591.94 3221.34
   0 2347.04 2591.94 3110.03
   0 2296.06 2591.94 2976.21
   0 2289.50 2591.94 3015.82
   0 2289.61 2591.94 3032.19
   0 2278.37 2591.94 3014.59
   0 2285.70 2591.94 3032.06