Measuring CPU utlization

this measurement is actually meaningless in RTX. in Linux systems, the scheduler has window of a predetermined size in which tasks are executed; if there is time left in it, the idle task is run. but RTX does not work like that. what you can do it use the __weak function void rt_post_taskswitch(U32 new_task) to log the timestamp at which a context switch has occured (use a free running hardware timer for that). it is called when a context switch happens. maybe you can compute how much of its time slice each task has consumed every period of something similar.

this measurement is actually meaningless in RTX. in Linux systems, the scheduler has window of a predetermined size in which tasks are executed; if there is time left in it, the idle task is run. but RTX does not work like that. what you can do it use the __weak function void rt_post_taskswitch(U32 new_task) to log the timestamp at which a context switch has occured (use a free running hardware timer for that). it is called when a context switch happens. maybe you can compute how much of its time slice each task has consumed every period of something similar.

Hello Tamir,

Why do you think, this approach wont work in RTX?

Even if RTX is preemptive and doesn't have a fixed window size to execute tasks, I believe, then also this approach could give a measure of CPU idle time. Isnt it?

If i use context switching to save a timer value, then also i need to check for idle task's id etc...and then its just a matter of using a time difference right away instead of using variables.

Am I missing something?

Thanks & Best Regards,
Vivek

Vivek,

the fact that the idle task is not executed does not mean the processor is 100% loaded. proof? you can probably add a task that needs to wait for a predetermined period before waking up (even quite often) and it will probably never miss its deadline.

"the fact that the idle task is not executed does not mean the processor is 100% loaded. proof? you can probably add a task that needs to wait for a predetermined period before waking up (even quite often) and it will probably never miss its deadline."

Is that proof?

You can always add a task and have it run without it missing it's deadline so long as the priorities are suitable. (i.e., higher priority than others that are ready to run.)

Those lower priority tasks will still be consuming CPU cycles if they're ready to run.

ok, it's not "proof" - I just wanted to demonstrate that one cannot conclude anything based on idle task.