rtla tools：When I attempted to test the osnoise using the SCHED_DEADLINE scheduling policy, I encountered the error:

Failed to set sched attributes to the pid xxx: Operation not permitted 
Error setting sched attributes for pid:xxx
Failed to set sched parameters

The command I used was:

timerlat hist -d 10m -c 0-3 -P d:100us:1ms

Why does this situation occur?

Debugging in the kernel, I found that this part of the code was causing the error:

/kernel/sched/core.c  __sched_setscheduler():
if (dl_bandwidth_enabled() && dl_policy(policy) &&
                !(attr->sched_flags & SCHED_FLAG_SUGOV)) {
            cpumask_t *span = rq->rd->span;

            /*
             * Don't allow tasks with an affinity mask smaller than
             * the entire root_domain to become SCHED_DEADLINE. We
             * will also fail if there's no bandwidth available.
             */
            if (!cpumask_subset(span, p->cpus_ptr) ||
                rq->rd->dl_bw.bw == 0) {
                retval = -EPERM;
                goto unlock;
            }
        }

I ran an “example of using the SCHED_DEADLINE scheduling policy[https://www.kernel.org/doc/html/latest/scheduler/sched-deadline.html]” ，everything is OK