Lee Revell wrote:
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.
And even then the task would need to be in the kernel and would be preempted
when it exits the kernel.
--
George Anzinger [email protected]
HRT (High-res-timers): http://sourceforge.net/projects/high-res-timers/
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