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.\" Copyright (C) Tom Bjorkholm & Markus Kuhn, 1996
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.\" 1996-04-01 Tom Bjorkholm <tomb@mydata.se>
.\"            First version written
.\" 1996-04-10 Markus Kuhn <mskuhn@cip.informatik.uni-erlangen.de>
.\"            revision
.\"
.TH SCHED_RR_GET_INTERVAL 2 2011-10-16 "Linux" "Linux Programmer's Manual"
.SH NAME
sched_rr_get_interval \- get the SCHED_RR interval for the named process
.SH SYNOPSIS
.B #include <sched.h>
.sp
.BI "int sched_rr_get_interval(pid_t " pid ", struct timespec * " tp );
.SH DESCRIPTION
.BR sched_rr_get_interval ()
writes into the
.I timespec
structure pointed to by
.I tp
the round-robin time quantum for the process identified by
.IR pid .
The specified process should be running under the
.B SCHED_RR
scheduling policy.

The
.I timespec
structure has the following form:

.in +4n
.nf
struct timespec {
    time_t tv_sec;    /* seconds */
    long   tv_nsec;   /* nanoseconds */
};
.fi
.in

If
.I pid
is zero, the time quantum for the calling process is written into
.IR *tp .
.\" FIXME . On Linux, sched_rr_get_interval()
.\" returns the timeslice for SCHED_OTHER processes -- this timeslice
.\" is influenced by the nice value.
.\" For SCHED_FIFO processes, this always returns 0.
.\"
.\" The round-robin time quantum value is not alterable under Linux
.\" 1.3.81.
.\"
.SH "RETURN VALUE"
On success,
.BR sched_rr_get_interval ()
returns 0.
On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
.TP
.B EFAULT
Problem with copying information to user space.
.TP
.B EINVAL
Invalid pid.
.TP
.B ENOSYS
The system call is not yet implemented (only on rather old kernels).
.TP
.B ESRCH
Could not find a process with the ID
.IR pid .
.SH "CONFORMING TO"
POSIX.1-2001.
.SH NOTES
POSIX systems on which
.BR sched_rr_get_interval ()
is available define
.B _POSIX_PRIORITY_SCHEDULING
in
.IR <unistd.h> .
.SS Linux Notes
POSIX does not specify any mechanism for controlling the size of the
round-robin time quantum.
Older Linux kernels provide a (nonportable) method of doing this.
The quantum can be controlled by adjusting the process's nice value (see
.BR setpriority (2)).
Assigning a negative (i.e., high) nice value results in a longer quantum;
assigning a positive (i.e., low) nice value results in a shorter quantum.
The default quantum is 0.1 seconds;
the degree to which changing the nice value affects the
quantum has varied somewhat across kernel versions.
Since Linux 2.6.24,
.\" commit a4ec24b48ddef1e93f7578be53270f0b95ad666c
the
.BR SCHED_RR
quantum cannot be modified.
.\" .SH BUGS
.\" As of Linux 1.3.81
.\" .BR sched_rr_get_interval ()
.\" returns with error
.\" ENOSYS, because SCHED_RR has not yet been fully implemented and tested
.\" properly.
.SH "SEE ALSO"
.BR sched_setscheduler (2)
has a description of the Linux scheduling scheme.
.PP
.I Programming for the real world \- POSIX.4
by Bill O. Gallmeister, O'Reilly & Associates, Inc., ISBN 1-56592-074-0.
.SH COLOPHON
This page is part of release 3.44 of the Linux
.I man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.