man2/sched_get_priority_max.2

   1 .\" Copyright (C) Tom Bjorkholm & Markus Kuhn, 1996
   2 .\"
   3 .\" SPDX-License-Identifier: GPL-2.0-or-later
   4 .\"
   5 .\" 1996-04-01 Tom Bjorkholm <tomb@mydata.se>
   6 .\"            First version written
   7 .\" 1996-04-10 Markus Kuhn <mskuhn@cip.informatik.uni-erlangen.de>
   8 .\"            revision
   9 .\"
  10 .TH SCHED_GET_PRIORITY_MAX 2 2021-03-22 "Linux man-pages (unreleased)" "Linux Programmer's Manual"
  11 .SH NAME
  12 sched_get_priority_max, sched_get_priority_min  \- get static priority range
  13 .SH LIBRARY
  14 Standard C library
  15 .RI ( libc ", " \-lc )
  16 .SH SYNOPSIS
  17 .nf
  18 .B #include <sched.h>
  19 .PP
  20 .BI "int sched_get_priority_max(int " policy );
  21 .BI "int sched_get_priority_min(int " policy );
  22 .fi
  23 .SH DESCRIPTION
  24 .BR sched_get_priority_max ()
  25 returns the maximum priority value that can be used with the
  26 scheduling algorithm identified by
  27 .IR policy .
  28 .BR sched_get_priority_min ()
  29 returns the minimum priority value that can be used with the
  30 scheduling algorithm identified by
  31 .IR policy .
  32 Supported
  33 .I policy
  34 values are
  35 .BR SCHED_FIFO ,
  36 .BR SCHED_RR ,
  37 .BR SCHED_OTHER ,
  38 .BR SCHED_BATCH ,
  39 .BR SCHED_IDLE ,
  40 and
  41 .BR SCHED_DEADLINE .
  42 Further details about these policies can be found in
  43 .BR sched (7).
  44 .PP
  45 Processes with numerically higher priority values are scheduled before
  46 processes with numerically lower priority values.
  47 Thus, the value
  48 returned by
  49 .BR sched_get_priority_max ()
  50 will be greater than the
  51 value returned by
  52 .BR sched_get_priority_min ().
  53 .PP
  54 Linux allows the static priority range 1 to 99 for the
  55 .B SCHED_FIFO
  56 and
  57 .B SCHED_RR
  58 policies, and the priority 0 for the remaining policies.
  59 Scheduling priority ranges for the various policies
  60 are not alterable.
  61 .PP
  62 The range of scheduling priorities may vary on other POSIX systems,
  63 thus it is a good idea for portable applications to use a virtual
  64 priority range and map it to the interval given by
  65 .BR sched_get_priority_max ()
  66 and
  67 .BR sched_get_priority_min ()
  68 POSIX.1 requires
  69 .\" POSIX.1-2001, POSIX.1-2008 (XBD 2.8.4)
  70 a spread of at least 32 between the maximum and the minimum values for
  71 .B SCHED_FIFO
  72 and
  73 .BR SCHED_RR .
  74 .PP
  75 POSIX systems on which
  76 .BR sched_get_priority_max ()
  77 and
  78 .BR sched_get_priority_min ()
  79 are available define
  80 .B _POSIX_PRIORITY_SCHEDULING
  81 in
  82 .IR <unistd.h> .
  83 .SH RETURN VALUE
  84 On success,
  85 .BR sched_get_priority_max ()
  86 and
  87 .BR sched_get_priority_min ()
  88 return the maximum/minimum priority value for the named scheduling
  89 policy.
  90 On error, \-1 is returned, and
  91 .I errno
  92 is set to indicate the error.
  93 .SH ERRORS
  94 .TP
  95 .B EINVAL
  96 The argument
  97 .I policy
  98 does not identify a defined scheduling policy.
  99 .SH STANDARDS
 100 POSIX.1-2001, POSIX.1-2008.
 101 .SH SEE ALSO
 102 .ad l
 103 .nh
 104 .BR sched_getaffinity (2),
 105 .BR sched_getparam (2),
 106 .BR sched_getscheduler (2),
 107 .BR sched_setaffinity (2),
 108 .BR sched_setparam (2),
 109 .BR sched_setscheduler (2),
 110 .BR sched (7)