On 01/03/06, Philippe Gerum <[EMAIL PROTECTED]> wrote:
Dmitry Adamushko wrote:
> On 01/03/06, *Philippe Gerum* <[EMAIL PROTECTED] <mailto:[EMAIL PROTECTED]>>
> wrote:
>      The other option I've described for
>     dealing with overruns in rt_task_wait_period would be as follows:
>     - save the count of overruns
>     - clear the count of overruns  /* i.e. "purge" */
>     - return both the saved count and -ETIMEDOUT to the user.
>     This way, rt_task_wait_period would return only once with an error
>     status, telling
>     the user about the exact count of pending overruns in the same time.
> I definitely agree with you here.
> IMHO, there is no point in calling rt_task_wait_period() a few
> times in a row just to clean up the "poverrun" counter
> (if there were a few overruns) when the whole may be reported at once.
> This former way just gives unnecessary overhead.

My concern is that some recovery procedure might require to get the exact number
of pending overruns to operate properly in order to catch up with the missing
expiries, and there is no way to get this information out of the current API (!).
Even calling rt_task_wait_period in loop and testing for -ETIMEDOUT is unusable,
since well, we would obviously get blocked when the overrun count drops to zero,
which is not what we want in order to be able to run the recovery procedure asap.

All in all, I would vote for changing the current rt_task_wait_period() interface.

> Actually, there is a kind of application that must not rely on
> the "poverrun" counter, the klatency/latency utility and alike.
> They are run normally (at least at the very first time) in the untrusted
> environment
> where SMI or something similar - that may prevent a CPU from handling normal
> interrupts for quite a long time - make occur happily.
> As the "poeverrun" counting is dependent on the timer interrupt,
> it becomes irrelevant.
> Something like
> overruns = (real_time_of_wakeup - desired_time_of_wakeup) / period (*)
> should be rather used there (of course, the timing source must not be
> interrupt-dependent).

Ah! you know what, I'm pretty sure that one of your very first public posts on the
RTAI/fusion mailing list at that time, was exactely about this issue :o)

Good memory indeed; so it's too earlier for you to get retired :o)



Best regards,
Dmitry Adamushko
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