WQ: Iterate whole ready list if task priority has been set

[colinthomas-z80]

Proposed Changes

Addresses #4276

We cannot partially iterate the ready list and leave it out of order if we wish to maintain priority scheduling. If a task priority is set by the user, revert to iterating the entire list each scheduling attempt.

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[btovar]

ready to merge?

[dthain]

Hold on a minute...

[dthain]

I don't think send_one_task has the desired effect. If no tasks are schedulable, it will rotate through the entire list, yes. But if it starts working through the list and finds one halfway, then it will return after rotating half the list, and the priority order is lost. Or am I misunderstanding something?

[colinthomas-z80]

You're right I think. Maybe I can just switch back to list_iterate

[btovar]

list_rotate was added for performance advantages, right?
Would it be better to keep it and count how many rotations where done and then rotate back to the start if needed?

[colinthomas-z80]

That could get complicated quickly if we are pushing new tasks with priorities while the list is out of order

[btovar]

We can avoid the code duplication if you use a function pointer for whether to use list_nextitem or list_rotate, and update q->attempt_schedule_depth to the length of the ready_queue every time when using priorities.

[colinthomas-z80]

Is it necessary to call list_first_item before iterating the list normally?

[dthain]

Careful! You are iterating over the list but using list_pop_tail to remove a task. Those don't match up.