Re: 2.6.11 timeval_to_jiffies() wrong for ms resolution timers

[George Anzinger <george@mvista.com>]

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   george@mvista.com
HRT (High-res-timers):  http://sourceforge.net/projects/high-res-timers/