mirror of https://github.com/mkerrisk/man-pages
132 lines
3.8 KiB
Groff
132 lines
3.8 KiB
Groff
.\" Hey Emacs! This file is -*- nroff -*- source.
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.\"
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.\" Copyright (C) Tom Bjorkholm & Markus Kuhn, 1996
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.\"
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.\" This is free documentation; you can redistribute it and/or
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.\" modify it under the terms of the GNU General Public License as
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.\" published by the Free Software Foundation; either version 2 of
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.\" the License, or (at your option) any later version.
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.\"
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.\" The GNU General Public License's references to "object code"
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.\" and "executables" are to be interpreted as the output of any
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.\" document formatting or typesetting system, including
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.\" intermediate and printed output.
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.\"
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.\" This manual is distributed in the hope that it will be useful,
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.\" but WITHOUT ANY WARRANTY; without even the implied warranty of
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.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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.\" GNU General Public License for more details.
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.\"
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.\" You should have received a copy of the GNU General Public
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.\" License along with this manual; if not, write to the Free
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.\" Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111,
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.\" USA.
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.\"
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.\" 1996-04-01 Tom Bjorkholm <tomb@mydata.se>
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.\" First version written
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.\" 1996-04-10 Markus Kuhn <mskuhn@cip.informatik.uni-erlangen.de>
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.\" revision
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.\"
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.TH SCHED_RR_GET_INTERVAL 2 2011-10-16 "Linux" "Linux Programmer's Manual"
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.SH NAME
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sched_rr_get_interval \- get the SCHED_RR interval for the named process
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.SH SYNOPSIS
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.B #include <sched.h>
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.sp
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.BI "int sched_rr_get_interval(pid_t " pid ", struct timespec * " tp );
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.SH DESCRIPTION
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.BR sched_rr_get_interval ()
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writes into the
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.I timespec
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structure pointed to by
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.I tp
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the round-robin time quantum for the process identified by
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.IR pid .
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The specified process should be running under the
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.B SCHED_RR
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scheduling policy.
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The
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.I timespec
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structure has the following form:
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.in +4n
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.nf
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struct timespec {
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time_t tv_sec; /* seconds */
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long tv_nsec; /* nanoseconds */
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};
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.fi
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.in
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If
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.I pid
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is zero, the time quantum for the calling process is written into
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.IR *tp .
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.\" FIXME . On Linux, sched_rr_get_interval()
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.\" returns the timeslice for SCHED_OTHER processes -- this timeslice
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.\" is influenced by the nice value.
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.\" For SCHED_FIFO processes, this always returns 0.
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.\"
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.\" The round-robin time quantum value is not alterable under Linux
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.\" 1.3.81.
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.\"
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.SH "RETURN VALUE"
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On success,
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.BR sched_rr_get_interval ()
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returns 0.
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On error, \-1 is returned, and
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.I errno
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is set appropriately.
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.SH ERRORS
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.TP
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.B EFAULT
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Problem with copying information to user space.
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.TP
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.B EINVAL
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Invalid pid.
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.TP
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.B ENOSYS
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The system call is not yet implemented (only on rather old kernels).
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.TP
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.B ESRCH
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Could not find a process with the ID
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.IR pid .
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.SH "CONFORMING TO"
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POSIX.1-2001.
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.SH NOTES
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POSIX systems on which
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.BR sched_rr_get_interval ()
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is available define
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.B _POSIX_PRIORITY_SCHEDULING
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in
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.IR <unistd.h> .
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.SS Linux notes
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POSIX does not specify any mechanism for controlling the size of the
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round-robin time quantum.
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Older Linux kernels provide a (nonportable) method of doing this.
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The quantum can be controlled by adjusting the process's nice value (see
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.BR setpriority (2)).
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Assigning a negative (i.e., high) nice value results in a longer quantum;
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assigning a positive (i.e., low) nice value results in a shorter quantum.
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The default quantum is 0.1 seconds;
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the degree to which changing the nice value affects the
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quantum has varied somewhat across kernel versions.
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Since Linux 2.6.24,
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.\" commit a4ec24b48ddef1e93f7578be53270f0b95ad666c
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the
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.BR SCHED_RR
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quantum cannot be modified.
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.\" .SH BUGS
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.\" As of Linux 1.3.81
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.\" .BR sched_rr_get_interval ()
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.\" returns with error
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.\" ENOSYS, because SCHED_RR has not yet been fully implemented and tested
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.\" properly.
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.SH "SEE ALSO"
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.BR sched_setscheduler (2)
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has a description of the Linux scheduling scheme.
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.PP
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.I Programming for the real world \- POSIX.4
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by Bill O. Gallmeister, O'Reilly & Associates, Inc., ISBN 1-56592-074-0.
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