set default priority for ktimersoftd in linux with RT patch

Question

Is there a way to set the default priority for ktimersoftd/x so that it starts up with lets say a rt prio of -50 instead of doing chrt -p 49 pid of ktimersoftd/0 manually afterwards?

Thanx Andy

Answer 1

That's set in the kernel, in the following function in kernel/softirq.c:

static inline void ktimer_softirqd_set_sched_params(unsigned int cpu)
{
        struct sched_param param = { .sched_priority = 1 };
        
        sched_setscheduler(current, SCHED_FIFO, &param);
        
        /* Take over timer pending softirqs when starting */
        local_irq_disable();
        current->softirqs_raised = local_softirq_pending() & TIMER_SOFTIRQS;
        local_irq_enable();
}

So the only way is to patch the kernel and change 1 with something else. I'll be honest, I don't know the consequences of such a change. There's probably a reason why it's 1 and not 50.

NB: This function is only present in the kernel with PREEMPT_RT patch applied.