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RTPRIO(2) FreeBSD System Calls Manual RTPRIO(2)
NAME
rtprio, rtprio_thread - examine or modify realtime or idle priority
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <sys/types.h>
#include <sys/rtprio.h>
int
rtprio(int function, pid_t pid, struct rtprio *rtp);
int
rtprio_thread(int function, lwpid_t lwpid, struct rtprio *rtp);
DESCRIPTION
The rtprio() system call is used to lookup or change the realtime or idle
priority of a process, or the calling thread. The rtprio_thread() system
call is used to lookup or change the realtime or idle priority of a
thread.
The function argument specifies the operation to be performed.
RTP_LOOKUP to lookup the current priority, and RTP_SET to set the
priority.
For the rtprio() system call, the pid argument specifies the process to
operate on, 0 for the calling thread. When pid is non-zero, the system
call reports the highest priority in the process, or sets all threads'
priority in the process, depending on value of the function argument.
For the rtprio_thread() system call, the lwpid specifies the thread to
operate on, 0 for the calling thread.
The *rtp argument is a pointer to a struct rtprio which is used to
specify the priority and priority type. This structure has the following
form:
struct rtprio {
u_short type;
u_short prio;
};
The value of the type field may be RTP_PRIO_REALTIME for realtime
priorities, RTP_PRIO_NORMAL for normal priorities, and RTP_PRIO_IDLE for
idle priorities. The priority specified by the prio field ranges between
0 and RTP_PRIO_MAX (usually 31). 0 is the highest possible priority.
Realtime and idle priority is inherited through fork() and exec().
A realtime thread can only be preempted by a thread of equal or higher
priority, or by an interrupt; idle priority threads will run only when no
other real/normal priority thread is runnable. Higher real/idle priority
threads preempt lower real/idle priority threads. Threads of equal
real/idle priority are run round-robin.
RETURN VALUES
[EFAULT] The rtp pointer passed to rtprio() or rtprio_thread()
was invalid.
[EINVAL] The specified prio was out of range.
[EPERM] The calling thread is not allowed to set the priority.
Only root is allowed to change the realtime or idle
priority of any thread. Exceptional privileges can be
granted through the mac_priority(4) policy and the
realtime and idletime user groups. The sysctl(8)
variable security.bsd.unprivileged_idprio is
deprecated. If set to non-zero, it lets any user
change the idle priority of threads they own.
[ESRCH] The specified process or thread was not found or
visible.
SEE ALSO
nice(1), ps(1), rtprio(1), setpriority(2), nice(3), mac_priority(4),
renice(8), p_cansee(9)
AUTHORS
The original author was Henrik Vestergaard Draboel <hvd@terry.ping.dk>.
This implementation in FreeBSD was substantially rewritten by David
Greenman. The rtprio_thread() system call was implemented by David Xu.
FreeBSD 14.0-RELEASE-p11 December 8, 2021 FreeBSD 14.0-RELEASE-p11