1 .\" Copyright (C) Tom Bjorkholm & Markus Kuhn, 1996
3 .\" %%%LICENSE_START(GPLv2+_doc_full)
4 .\" This is free documentation; you can redistribute it and/or
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17 .\" GNU General Public License for more details.
19 .\" You should have received a copy of the GNU General Public
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21 .\" <http://www.gnu.org/licenses/>.
24 .\" 1996-04-01 Tom Bjorkholm <tomb@mydata.se>
25 .\" First version written
26 .\" 1996-04-10 Markus Kuhn <mskuhn@cip.informatik.uni-erlangen.de>
29 .TH SCHED_RR_GET_INTERVAL 2 2011-10-16 "Linux" "Linux Programmer's Manual"
31 sched_rr_get_interval \- get the SCHED_RR interval for the named process
35 .BI "int sched_rr_get_interval(pid_t " pid ", struct timespec * " tp );
37 .BR sched_rr_get_interval ()
40 structure pointed to by
42 the round-robin time quantum for the process identified by
44 The specified process should be running under the
50 structure has the following form:
55 time_t tv_sec; /* seconds */
56 long tv_nsec; /* nanoseconds */
63 is zero, the time quantum for the calling process is written into
65 .\" FIXME . On Linux, sched_rr_get_interval()
66 .\" returns the timeslice for SCHED_OTHER processes -- this timeslice
67 .\" is influenced by the nice value.
68 .\" For SCHED_FIFO processes, this always returns 0.
70 .\" The round-robin time quantum value is not alterable under Linux
75 .BR sched_rr_get_interval ()
77 On error, \-1 is returned, and
83 Problem with copying information to user space.
89 The system call is not yet implemented (only on rather old kernels).
92 Could not find a process with the ID
97 POSIX systems on which
98 .BR sched_rr_get_interval ()
100 .B _POSIX_PRIORITY_SCHEDULING
104 POSIX does not specify any mechanism for controlling the size of the
105 round-robin time quantum.
106 Older Linux kernels provide a (nonportable) method of doing this.
107 The quantum can be controlled by adjusting the process's nice value (see
108 .BR setpriority (2)).
109 Assigning a negative (i.e., high) nice value results in a longer quantum;
110 assigning a positive (i.e., low) nice value results in a shorter quantum.
111 The default quantum is 0.1 seconds;
112 the degree to which changing the nice value affects the
113 quantum has varied somewhat across kernel versions.
115 .\" commit a4ec24b48ddef1e93f7578be53270f0b95ad666c
118 quantum cannot be modified.
120 .\" As of Linux 1.3.81
121 .\" .BR sched_rr_get_interval ()
122 .\" returns with error
123 .\" ENOSYS, because SCHED_RR has not yet been fully implemented and tested
126 .BR sched_setscheduler (2)
127 has a description of the Linux scheduling scheme.
129 .I Programming for the real world \- POSIX.4
130 by Bill O. Gallmeister, O'Reilly & Associates, Inc., ISBN 1-56592-074-0.