Delays, clocks, timers, hrtimers, etc

[Russell King - ARM Linux]

On Fri, Feb 06, 2015 at 06:21:37PM -0800, Mason wrote:
> Also, reading arch/arm/kernel/smp_twd.c, I see that frequency changes
> due to cpufreq are properly accounted for. (Although I imagine they do
> introduce a small error in time-keeping because moving from freq_A to
> freq_B is not instantaneous, so the exact time elapsed in-between is
> impossible to determine.)

TWD is not used for time keeping as such.  As I explained in one of my
previous emails, local timers are used to signal events.

The active clocksource is used to determine the passing of time-of-day,
and sched_clock is used to account for process time by the scheduler.

An early/late/missed local timer interrupt has no impact on time keeping.

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