get_tsc_coeff

Nasty tool that reads coefficients used to convert TSC tick deltas into nanosecond deltas, from the vvar data page mapped by the kernel into a process.

(why would you ever need this?)

Build

The project uses the meson build system.

Make sure libbpf and its dependencies are available, and then build like any other meson C project.

libbpf is only used to process kernel BTF, in a rudimentary "kernel compatability check" to ensure the tool won't run on kernels that are definitely incompatible.

meson setup builddir
ninja -C builddir

To attempt linking libbpf statically, setup the build director with:

meson setup -Dlibbpf_static=true builddir

Watch out for warnings about static versions of libbpf's own dependencies not being found.

Run

This program relies on a bunch of private vvar details. It may return bogus values or crash. You have been warned.

# obtain the coefficients used to map TSC ticks to CLOCK_MONOTONIC
# nanoseconds
builddir/get_tsc_coeff
reading CLOCK_MONOTONIC coefficients
ns = (tsc * 4909275) >> 24

# obtain the coefficients used to map TSC ticks to CLOCK_MONOTONIC_RAW
builddir/get_tsc_coeff raw
reading CLOCK_MONOTONIC_RAW coefficients
ns = (tsc * 4909064) >> 24