rtprio(2) [freebsd man page]
RTPRIO(2) BSD 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 sys- tem call reports the highest priority in the process, or sets all threads' priority in the process, depending on value of the function argu- ment. 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 prior- ity. 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
The rtprio() and rtprio_thread() functions return the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error. ERRORS
The rtprio() and rtprio_thread() system calls will fail if: [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 realtime priority. Only root is allowed to change the realtime priority of any thread, and non-root may only change the idle priority of threads the user owns, when the sysctl(8) variable security.bsd.unprivileged_idprio is set to non-zero. [ESRCH] The specified process or thread was not found or visible. SEE ALSO
nice(1), ps(1), rtprio(1), setpriority(2), nice(3), 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. BSD
December 27, 2011 BSD
Check Out this Related Man Page
RTPRIO(1) BSD General Commands Manual RTPRIO(1) NAME
rtprio, idprio -- execute, examine or modify a utility's or process's realtime or idletime scheduling priority SYNOPSIS
[id|rt]prio [id|rt]prio [-]pid [id|rt]prio priority command [args] [id|rt]prio priority -pid [id|rt]prio -t command [args] [id|rt]prio -t -pid DESCRIPTION
The rtprio utility is used for controlling realtime process scheduling. The idprio utility is used for controlling idletime process scheduling, and can be called with the same options as rtprio. A process with a realtime priority is not subject to priority degradation, and will only be preempted by another process of equal or higher realtime priority. A process with an idle priority will run only when no other process is runnable and then only if its idle priority is equal or greater than all other runnable idle priority processes. Both rtprio or idprio when called without arguments will return the realtime priority of the current process. If rtprio is called with 1 argument, it will return the realtime priority of the process with the specified pid. If priority is specified, the process or program is run at that realtime priority. If -t is specified, the process or program is run as a normal (non-realtime) process. If -pid is specified, the process with the process identifier pid will be modified, else if command is specified, that program is run with its arguments. Priority is an integer between 0 and RTP_PRIO_MAX (usually 31). 0 is the highest priority Pid of 0 means "the current process". Only root is allowed to set realtime or idle priority for a process. A user may modify the idle priority of their own processes if the sysctl(8) variable security.bsd.unprivileged_idprio is set to non-zero. Note that this increases the chance that a deadlock can occur if a process locks a required resource and then does not get to run. EXIT STATUS
If rtprio execute a command, the exit value is that of the command executed. In all other cases, rtprio exits 0 on success, and 1 for all other errors. EXAMPLES
To see which realtime priority the current process is at: rtprio To see which realtime priority of process 1423: rtprio 1423 To run cron(8) at the lowest realtime priority: rtprio 31 cron To change the realtime priority of process 1423 to 16: rtprio 16 -1423 To run tcpdump(1) without realtime priority: rtprio -t tcpdump To change the realtime priority of process 1423 to RTP_PRIO_NORMAL (non-realtime/normal priority): rtprio -t -1423 To make depend while not disturbing other machine usage: idprio 31 make depend SEE ALSO
nice(1), ps(1), rtprio(2), setpriority(2), nice(3), renice(8) HISTORY
The rtprio utility appeared in FreeBSD 2.0, but is similar to the HP-UX version. AUTHORS
Henrik Vestergaard Draboel <hvd@terry.ping.dk> is the original author. This implementation in FreeBSD was substantially rewritten by David Greenman. CAVEATS
You can lock yourself out of the system by placing a cpu-heavy process in a realtime priority. BUGS
There is no way to set/view the realtime priority of process 0 (swapper) (see ps(1)). There is in FreeBSD no way to ensure that a process page is present in memory therefore the process may be stopped for pagein (see mprotect(2), madvise(2)). Under FreeBSD system calls are currently never preempted, therefore non-realtime processes can starve realtime processes, or idletime pro- cesses can starve normal priority processes. BSD
September 29, 2012 BSD