[AZURE RTOS][SMP] Azure rtos SMP flow

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[AZURE RTOS][SMP] Azure rtos SMP flow

igenS 21

Hi ,
I have query ,this is more related to clarifying if my understanding of Threadx-SMP flow is correct .

1) In Smp mode (taken Cortex_a7_smp as reference) , Timer interrupt goes only to Primary core.

2) Primary core only , runs scheduler code ,bookkeeping operation (like time slice decrement ,etc ) of all threads (threads running on primary core and secondary core ) is done by core 0 on each tick.
When a time slice of thread running on secondary core expires, primary core updates the thread_execute pointer of secondary core with next thread
and generates the IPI for secondary core.

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Scott Azure RTOS 4,051

The ThreadX timer thread can execute on any core. I believe in some of our examples (e.g. https://github.com/azure-rtos/threadx/blob/master/ports_smp/cortex_a53_smp/ac6/example_build/sample_threadx/timer_interrupts.c#L57-#L59) the timer is set to interrupt only core 0. That is just example code we used from ARM.
No. The scheduler will run on any core (and do housekeeping like updating time slice).

igenS 21 Reputation points

2022-08-23T17:25:10.533+00:00

Thanks Scott for your reply.

I am little confused from your below reply
No. The scheduler will run on any core (and do housekeeping like updating time slice).

Did you mean that at any time t ,scheduler is running on all the cores

But i think scheduler will run on only the core to which timer tick is routed, my conclusion is based on below observations

Today ,we booted azure on our board in SMP mode ,for which we routed timer tick to core 0 {we selected core 0 as primary core} ,
We are able to see task running on all core and we have not enabled any timer interrupt handling on other cores.

Is it like we can boot threadx in SMP in 2 ways :

1) Routing tick to one core and other cores relying on IPI for scheduling the task ?

2) We can route tick to all the cores ,and each handling scheduler by itself ?

Can you point me to any doc where i can find in-depth Threadx Rtos internals .
Scott Azure RTOS 4,051 Reputation points

2022-08-23T18:19:46.557+00:00

The scheduler has the ability to run on any core. For example, if a thread running on core 1 suspends, the scheduler will run on that core to determine what thread will run next.
It is possible that the scheduler will be running on all cores at once, for example if all threads are sleeping.

Correct, ThreadX SMP can be run in either of those two ways. There is more info in the defines here: https://learn.microsoft.com/en-us/azure/rtos/threadx/threadx-smp/chapter2
(see TX_THREAD_SMP_INTER_CORE_INTERRUPT and TX_THREAD_SMP_ONLY_CORE_0_DEFAULT). For the Cortex-A7, TX_THREAD_SMP_INTER_CORE_INTERRUPT is defined in tx_port.h.
Let me know if you have further questions.
igenS 21 Reputation points

2022-08-24T17:14:19.223+00:00

Our test results now look inline with your comments.

Will try booting SMP ,with timer interrupt routed to all the core.
And if any doubt in that flow will raise a new ticket.
Thanks for clarifying the doubts.

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[AZURE RTOS][SMP] Azure rtos SMP flow

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