rtprio(2) [debian man page]
RTPRIO(2) BSD System Calls Manual RTPRIO(2) NAME
rtprio -- examine or modify a process 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); DESCRIPTION
The rtprio() system call is used to lookup or change the realtime or idle priority of a process. The function argument specifies the operation to be performed. RTP_LOOKUP to lookup the current priority, and RTP_SET to set the priority. The pid argument specifies the process to be used, 0 for the current process. 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 process can only be preempted by a process of equal or higher priority, or by an interrupt; idle priority processes will run only when no other real/normal priority process is runnable. Higher real/idle priority processes preempt lower real/idle priority processes. Processes of equal real/idle priority are run round-robin. RETURN VALUES
The rtprio() function returns 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() system call will fail if [EINVAL] The specified prio was out of range. [EPERM] The calling process is not allowed to set the realtime priority. Only root is allowed to change the realtime priority of any process, and non-root may only change the idle priority of the current process. [ESRCH] The specified process was not found. SEE ALSO
nice(1), ps(1), rtprio(1), setpriority(2), nice(3), renice(8) AUTHORS
The original author was Henrik Vestergaard Draboel <hvd@terry.ping.dk>. This implementation in FreeBSD was substantially rewritten by David Greenman. BSD
July 23, 1994 BSD
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rtprio(2) System Calls Manual rtprio(2) NAME
rtprio - change or read real-time priority SYNOPSIS
DESCRIPTION
The system call sets or reads the real-time priority of a process. If pid is zero, it specifies the calling process; otherwise, it specifies the process ID of a process. If the process pid contains more than one thread or a lightweight process (that is, the process is multi-threaded), this function shall only change the process scheduling policy and priority. Individual threads or lightweight processes in the target process shall not have their scheduling policies and priorities modified. Note that if the target process is multi-threaded, this process scheduling policy and priority change will only affect a child process that is created later and inherits its parent's scheduling policy and priority. The priority returned is the value of the target's old prior- ity, though individual threads or lightweight processes may have a different value if some other interface is used to change an individual thread or lightweight processes priority. When setting the real-time priority of another process, the real or effective user ID of the calling process must match the real or saved user ID of the process to be modified, or the effective user ID of the calling process must be that of a user having appropriate privi- leges. The calling process must also be a member of a privilege group allowing (see getprivgrp(2)) or the effective user ID of the calling process must be a user having appropriate privileges. Simply reading real-time priorities requires no special privilege. Real-time scheduling policies differ from normal timesharing policies in that the real-time priority is used to absolutely order all real- time processes. This priority is not degraded over time. All real-time processes are of higher priority than normal user and system pro- cesses, although some system processes may run at real-time priorities. If there are several eligible processes at the same priority level, they are run in a round robin fashion as long as no process with a higher priority intervenes. A real-time process receives CPU service until it either voluntarily gives up the CPU or is preempted by a process of equal or higher priority. Interrupts can also preempt a real-time process. Valid real-time priorities run from zero to 127. Zero is the highest (most important) priority. This real-time priority is inherited across forks (see fork(2)) and execs (see exec(2)). prio can have the following values: Set the process to this real-time priority. Do not change the real-time priority. This is used to read the process real-time priority. Set the process to no longer have a real-time priority. It resumes a normal timesharing priority. Any process, regardless of privilege, is allowed to turn off its own real-time priority using a pid of zero. Security Restrictions Some or all of the actions associated with this system call are subject to compartmental restrictions. See compartments(5) for more infor- mation about compartmentalization on systems that support that feature. Compartmental restrictions can be overridden if the process pos- sesses the privilege Processes owned by the superuser may not have this privilege. Processes owned by any user may have this privilege, depending on system configuration. Some or all of the actions associated with this system call require one or more privileges. Processes owned by the superuser have many, though not all, privileges. Processes owned by other users may have privilege(s), depending on system configuration. See privileges(5) for more information about privileged access on systems that support fine-grained privileges. RETURN VALUE
returns the following values: The process was a real-time process. The value is the process's former (before the call) real-time priority. The process was not a real-time process. An error occurred. is set to indicate the error. ERRORS
If fails, is set to one of the following values: The target process could not be accessed due to compartmental restrictions. prio is not or in the range 0 to 127. The calling process is not a user having appropriate privileges, and neither its real nor effective user ID match the real or saved user ID of the process indicated by pid. The group access list of the calling process does not contain a group having capability and prio is not or with a pid of zero. No process can be found corresponding to that specified by pid. EXAMPLES
The following call to sets the calling process to a real-time priority of 90: WARNINGS
Normally, compute-bound programs should not be run at real-time priorities, because all timesharing work on the CPU would come to a com- plete halt. DEPENDENCIES
Because processes executing at real-time priorities get scheduling preference over a system process executing at a lower priority, unex- pected system behavior can occur after a power failure on systems that support power-fail recovery. For example, when (see init(1M)) receives the powerfail signal it normally reloads programmable hardware such as terminal multiplexers. If a higher-priority real-time process is eligible to run after the power failure, the running of is delayed. This condition temporarily prevents terminal input to any process, including real-time shells of higher priority than the eligible real-time process. To avoid this situation, a real-time process should catch and suspend itself until has finished its powerfail processing. AUTHOR
was developed by HP. SEE ALSO
rtprio(1), getprivgrp(2), nice(2), plock(2), privileges(5). rtprio(2)