Hi,
After some tests, it seems new tasks will inherit the parent
priority.
However for threads, given
On Sat, Apr 11, 2026 at 09:02:53PM +0100, Diego Nieto Cid wrote:
> kern/thread.c:338: thread_template.max_priority = BASEPRI_USER;
> kern/thread.c:422: *new_thread = thread_template;
and the following code in thread_create (kern/thread.c):
501 new_thread->priority = parent_task->priority;
This inherits the task priority which after
setpriority(PRIO_PROCESS, 0, -20) is set to 5.
502 if (pset->max_priority > new_thread->max_priority)
503 new_thread->max_priority = pset->max_priority;
The if above takes care of the max_priority of
the thread. The call to setpriority would change
the pset max priority to 5, but as it is not bigger
than BASEPRI_USER its body is not executed.
504 if (new_thread->max_priority > new_thread->priority)
505 new_thread->priority = new_thread->max_priority;
Finally, the thread priority is taken care of by
these two lines. As max_priority is bigger than 5,
the initial value set by parent_task->priority, it
is reset to that bigger value which happens to be
BASEPRI_USER (which comes from template_thread,
line 422, shown above in my previous email).
For short, as a result of this series of ifs, a thread is
always born with priority set to max_priority set to BASEPRI_USER.
No matter what the task priority or the processor set max_priority
is set to.
Does the setpriority call make any sense if the new threads do not
honor the very setting it is meant to change?
Taking max_priority out from the thread template could be a solution
but it looks quite a pervasive change.
Thanks,
Diego
