cpu_clock_sample_group
now = cpu_clock_sample_group(clkid, p, true);
now = cpu_clock_sample_group(clkid, tsk, true);
t = cpu_clock_sample_group(clkid, tsk, false);
now = cpu_clock_sample_group(clkid, p, !sigev_none);
now = cpu_clock_sample_group(clkid, p, false);