schedulersimplesmp priority lifo on executing

[Sebastian Huber]

On 2014-05-12 19:37, Jennifer Averett wrote:
> Attached is a scheduler simulator scenario, expected, and output files from one of
> the  tests for the smp simple scheduler.  It appears that tasks of
>   the same priority running on different cores are no longer selected for
> preemption in fifo order.  The executing list is FIFO per priority and the
> search is from the rear so the newest at a priority is selected, not
> the oldest.

Yes, this conforms to the requirements of the G-FP (global fixed priority) 
scheduler.  The highest priority (lowest priority number) threads get a 
processor assigned.  So in your scenario we start with four idle threads (id.prio):

i4.255 <= i3.255 <= i2.255 <= i1.255

Start tasks t1, t2, t3, t4 and t5.

t1.3 < t5.5 < t2.6 < t3.7 < t4.8 < i4.255 <= i3.255 <= i2.255 <= i1.255

Start tasks t6 and t7.  Please note that t6 has a lower priority than t5 (see 
also _Scheduler_priority_Enqueue()).  For example on a uni-processor system if 
you execute with priority X and start a task with priority X, then there will 
be no pre-emption.

t1.3 < t5.5 <= t6.5 <= t7.5 < t2.6 < t3.7 < t4.8 < i4.255 <= i3.255 <= i2.255 
<= i1.255

Start task t8.

t1.3 < t8.4 < t5.5 <= t6.5 <= t7.5 < t2.6 < t3.7 < t4.8 < i4.255 <= i3.255 <= 
i2.255 <= i1.255

This is why t8.4 uses the processor previously assigned to t7.5.

>
> This was confirmed on the simple SMP priority but should also be on
> the regular SMP priority. I just haven't confirmed it yet.
>
> This is the type of thing the scheduler simulator is very good at helping
> to root out. I don't know if a test exists to verify this behaviour. But it changed
> from the original implementation.
>
> Jennifer Averett
> On-Line Applications Research
>


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Sebastian Huber, embedded brains GmbH

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