[ECOS] eCos scheduler question

[ECOS] eCos scheduler question

[Daniel Lidsten]

Hi,

I have a question about when the eCos (multi-level) scheduler does a
reschedule
between my application threads.
(Reschedule = Each time the kernel checks if any more priority thread
shall run
instead of the current thread)

As far as I understand, a reschedule is done when one the following
happens:
* Each RTC tick (default 100/second)
* When a message is posted, a semaphore is signalled etc.
* When returning from an ISR (even if DSR is not used)

Anyone know if this is correct?

/Regards
Daniel

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[ECOS] eCos scheduler question 2

[Jose Souto]

Hi,

The documentation states that the tick is 10ms.
If I make it like 1ms, what impact should I expect in kernel overhead, task
switching, etc.. ?

Regards
Jose Luiz



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Re: [ECOS] eCos scheduler question

[Nick Garnett]

"Daniel Lidsten" <Daniel.Lidsten@combitechsystems.com> writes:

> As far as I understand, a reschedule is done when one the following
> happens:
> * Each RTC tick (default 100/second)
> * When a message is posted, a semaphore is signalled etc.
> * When returning from an ISR (even if DSR is not used)
>

Note that the first case here is exactly the same as the
third. There's nothing special about RTC ticks in this regard.

> Anyone know if this is correct?
> 

It is correct. eCos has a scheduler lock which is used to protect the
scheduler's data structures. Whenever the lock is released, the kernel
looks to see if there are any better threads to run. There are
various optimizations in the unlock code to avoid doing a full
scheduling operation if it is not necessary.

-- 
Nick Garnett - eCos Kernel Architect


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