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On Fri, 23 May 2003 17:19:39 +0200
Lukas Ruf <ruf@rawip.org> wrote:
>I would like to have a function that gets triggered every second to
>read the actual state of the counters, this function is called
>timed_func() later. The function should be triggered irrespective of
>the status of the other functionality /* I know about the race
>conditions... and the fact that the linux kernel is not
>interruptible per node */
>
>Ideas:
>
>In my mind the following ideas on came up how this problem could be
>solved in principle:
>
>a) implement timed_func() as a "normal" function in the same module
> -- this would be the easiest.
>
>b) implement timed_func() as a separate module-function. There, I
> assume there is no difference executionwise.
>
>c) implement timed_func() as an own kernel_thread such that it gets a
> schedulable entity.
>
>My Questions:
>
>- Is it possible to have timed_func() being launched every second in
> cases a) & b) or is the whole kernel module blocked until the
> function gets executed?
>
> If it would be possible to implement a) or b), how could I achieve
> this?
>
>- Is there another solution/idea that has not come to my mind so far?
The solution to your problem is really simple. You just need to
schedule a periodic kernel timer. This is the most straightforward
solution for your needs since kernel timer functions are always called
at just the right time even if the processor is executing a system
call. So what you need is simply a code like this one.
In module initialization
init_timer(&timer);
timer.expires = jiffies + HZ;
timer.function = handler;
add_timer(&timer);
Then, in handler() code put as last instructions,
timer.expires = jiffies + HZ;
add_timer(&timer);
When kernel timer function has been executed, it reschedules a new
kernel timer. If you have timer as global you don't need to define
again the field function. Obvioulsy, you can't assume that the next
call to handler() will be done after *exactly* HZ ticks but I think
that it's the easiest solution for your purposes.
PS If you have a copy of Linux Device Drivers please take a look at
page 203.
Regards.
- --
Angelo Dell'Aera 'buffer'
Antifork Research, Inc. http://buffer.antifork.org
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