On Thu, 2005-05-26 at 14:10 -0400, Richard B. Johnson wrote:
> The time for a sleeping (waiting) task to get the CPU is much
> greater than the jitter. Once in the ISR, some wake-up call
> is "scheduled" and the interrupt returns. A CPU hog may have
> been using the CPU when the interrupt occurred. It will continue
> to use the CPU until its time-slot (quantum) has expired. This
> could be a whole millisecond if HZ is 1000, 10 milliseconds if
> 100. It's only then that your sleeping task gets awakened
> by the interrupting event.
>
> So, accurate waking up is not guaranteed on any multi-user,
> multitasking system because you don't know what a user has
> been doing with the CPU. On a dedicated machine, one can
> have tasks that are most always sleeping or waiting for
> I/O so, the latency can come way down. However, signaling
> a task, based upon some time will never be very accurate
> anywhere.
Not quite, if your sleeping task has higher priority than the CPU hog it
will preempt the CPU hog immediately on return from the interrupt.
Unless you've disabled preemption of course, which would be stupid in
this case.
Lee
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