Multiple hardware timers in Linux

Question

Problem - There is an intermittent clock drift (of 2 seconds) on my Linux system, so once in a while the kernel timer threads get executed 2 seconds + timeout time

Question - There are multiple hardware clocksources (TSC, HPET, ACPI_PM), is it possible to create kernel timer threads that forcibly uses a secondary clocksource as a fallback, if the primary clocksource drifts..?

Answer 1

What you describe doesn't sound like clock drift (systematic error) but rather like lost timer interrupts. If you have another piece of hardware that can generate timed interrupts (HPET, RTC, but not TSC), you can make your time-sensitive processing from either the timer or the interrupt handler (or handlers), whichever happens first, you just need to design some kind of synchronization between them.

If you experience genuine clock drift, when the speed of your clock is less than real time, you can try to estimate it and compensate when timers are scheduled. But lost interrupts is a sign of a more serious problem and it makes sense to address the root cause, which may affect your secondary interrupt source as well.