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diff --git a/man2/sched_setscheduler.2 b/man2/sched_setscheduler.2 new file mode 100644 index 0000000..20ad5c2 --- /dev/null +++ b/man2/sched_setscheduler.2 @@ -0,0 +1,232 @@ +.\" Copyright (C) 2014 Michael Kerrisk <mtk.manpages@gmail.com> +.\" +.\" SPDX-License-Identifier: Linux-man-pages-copyleft +.\" +.\" +.TH sched_setscheduler 2 2023-03-30 "Linux man-pages 6.05.01" +.SH NAME +sched_setscheduler, sched_getscheduler \- +set and get scheduling policy/parameters +.SH LIBRARY +Standard C library +.RI ( libc ", " \-lc ) +.SH SYNOPSIS +.nf +.B #include <sched.h> +.PP +.BI "int sched_setscheduler(pid_t " pid ", int " policy , +.BI " const struct sched_param *" param ); +.BI "int sched_getscheduler(pid_t " pid ); +.fi +.SH DESCRIPTION +The +.BR sched_setscheduler () +system call +sets both the scheduling policy and parameters for the +thread whose ID is specified in \fIpid\fP. +If \fIpid\fP equals zero, the +scheduling policy and parameters of the calling thread will be set. +.PP +The scheduling parameters are specified in the +.I param +argument, which is a pointer to a structure of the following form: +.PP +.in +4n +.EX +struct sched_param { + ... + int sched_priority; + ... +}; +.EE +.in +.PP +In the current implementation, the structure contains only one field, +.IR sched_priority . +The interpretation of +.I param +depends on the selected policy. +.PP +Currently, Linux supports the following "normal" +(i.e., non-real-time) scheduling policies as values that may be specified in +.IR policy : +.TP 14 +.B SCHED_OTHER +the standard round-robin time-sharing policy; +.\" In the 2.6 kernel sources, SCHED_OTHER is actually called +.\" SCHED_NORMAL. +.TP +.B SCHED_BATCH +for "batch" style execution of processes; and +.TP +.B SCHED_IDLE +for running +.I very +low priority background jobs. +.PP +For each of the above policies, +.I param\->sched_priority +must be 0. +.PP +Various "real-time" policies are also supported, +for special time-critical applications that need precise control over +the way in which runnable threads are selected for execution. +For the rules governing when a process may use these policies, see +.BR sched (7). +The real-time policies that may be specified in +.I policy +are: +.TP 14 +.B SCHED_FIFO +a first-in, first-out policy; and +.TP +.B SCHED_RR +a round-robin policy. +.PP +For each of the above policies, +.I param\->sched_priority +specifies a scheduling priority for the thread. +This is a number in the range returned by calling +.BR sched_get_priority_min (2) +and +.BR sched_get_priority_max (2) +with the specified +.IR policy . +On Linux, these system calls return, respectively, 1 and 99. +.PP +Since Linux 2.6.32, the +.B SCHED_RESET_ON_FORK +flag can be ORed in +.I policy +when calling +.BR sched_setscheduler (). +As a result of including this flag, children created by +.BR fork (2) +do not inherit privileged scheduling policies. +See +.BR sched (7) +for details. +.PP +.BR sched_getscheduler () +returns the current scheduling policy of the thread +identified by \fIpid\fP. +If \fIpid\fP equals zero, the policy of the +calling thread will be retrieved. +.SH RETURN VALUE +On success, +.BR sched_setscheduler () +returns zero. +On success, +.BR sched_getscheduler () +returns the policy for the thread (a nonnegative integer). +On error, both calls return \-1, and +.I errno +is set to indicate the error. +.SH ERRORS +.TP +.B EINVAL +Invalid arguments: +.I pid +is negative or +.I param +is NULL. +.TP +.B EINVAL +.RB ( sched_setscheduler ()) +.I policy +is not one of the recognized policies. +.TP +.B EINVAL +.RB ( sched_setscheduler ()) +.I param +does not make sense for the specified +.IR policy . +.TP +.B EPERM +The calling thread does not have appropriate privileges. +.TP +.B ESRCH +The thread whose ID is \fIpid\fP could not be found. +.SH VERSIONS +POSIX.1 does not detail the permissions that an unprivileged +thread requires in order to call +.BR sched_setscheduler (), +and details vary across systems. +For example, the Solaris 7 manual page says that +the real or effective user ID of the caller must +match the real user ID or the save set-user-ID of the target. +.PP +The scheduling policy and parameters are in fact per-thread +attributes on Linux. +The value returned from a call to +.BR gettid (2) +can be passed in the argument +.IR pid . +Specifying +.I pid +as 0 will operate on the attributes of the calling thread, +and passing the value returned from a call to +.BR getpid (2) +will operate on the attributes of the main thread of the thread group. +(If you are using the POSIX threads API, then use +.BR pthread_setschedparam (3), +.BR pthread_getschedparam (3), +and +.BR pthread_setschedprio (3), +instead of the +.BR sched_* (2) +system calls.) +.SH STANDARDS +POSIX.1-2008 (but see BUGS below). +.PP +.B SCHED_BATCH +and +.B SCHED_IDLE +are Linux-specific. +.SH HISTORY +POSIX.1-2001. +.SH NOTES +Further details of the semantics of all of the above "normal" +and "real-time" scheduling policies can be found in the +.BR sched (7) +manual page. +That page also describes an additional policy, +.BR SCHED_DEADLINE , +which is settable only via +.BR sched_setattr (2). +.PP +POSIX systems on which +.BR sched_setscheduler () +and +.BR sched_getscheduler () +are available define +.B _POSIX_PRIORITY_SCHEDULING +in \fI<unistd.h>\fP. +.SH BUGS +POSIX.1 says that on success, +.BR sched_setscheduler () +should return the previous scheduling policy. +Linux +.BR sched_setscheduler () +does not conform to this requirement, +since it always returns 0 on success. +.SH SEE ALSO +.ad l +.nh +.BR chrt (1), +.BR nice (2), +.BR sched_get_priority_max (2), +.BR sched_get_priority_min (2), +.BR sched_getaffinity (2), +.BR sched_getattr (2), +.BR sched_getparam (2), +.BR sched_rr_get_interval (2), +.BR sched_setaffinity (2), +.BR sched_setattr (2), +.BR sched_setparam (2), +.BR sched_yield (2), +.BR setpriority (2), +.BR capabilities (7), +.BR cpuset (7), +.BR sched (7) +.ad |