man2/sched_get_priority_max.2

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  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>
  27 .\"            revision
  28 .\"
  29 .TH SCHED_GET_PRIORITY_MAX 2 2017-09-15 "Linux" "Linux Programmer's Manual"
  30 .SH NAME
  31 sched_get_priority_max, sched_get_priority_min  \- get static priority range
  32 .SH SYNOPSIS
  33 .B #include <sched.h>
  34 .PP
  35 .BI "int sched_get_priority_max(int " policy );
  36 .PP
  37 .BI "int sched_get_priority_min(int " policy );
  38 .SH DESCRIPTION
  39 .BR sched_get_priority_max ()
  40 returns the maximum priority value that can be used with the
  41 scheduling algorithm identified by
  42 .IR policy .
  43 .BR sched_get_priority_min ()
  44 returns the minimum priority value that can be used with the
  45 scheduling algorithm identified by
  46 .IR policy .
  47 Supported
  48 .I policy
  49 values are
  50 .BR SCHED_FIFO ,
  51 .BR SCHED_RR ,
  52 .BR SCHED_OTHER ,
  53 .BR SCHED_BATCH ,
  54 .BR SCHED_IDLE ,
  55 and
  56 .BR SCHED_DEADLINE .
  57 Further details about these policies can be found in
  58 .BR sched (7).
  59 .PP
  60 Processes with numerically higher priority values are scheduled before
  61 processes with numerically lower priority values.
  62 Thus, the value
  63 returned by
  64 .BR sched_get_priority_max ()
  65 will be greater than the
  66 value returned by
  67 .BR sched_get_priority_min ().
  68 .PP
  69 Linux allows the static priority range 1 to 99 for the
  70 .B SCHED_FIFO
  71 and
  72 .B SCHED_RR
  73 policies, and the priority 0 for the remaining policies.
  74 Scheduling priority ranges for the various policies
  75 are not alterable.
  76 .PP
  77 The range of scheduling priorities may vary on other POSIX systems,
  78 thus it is a good idea for portable applications to use a virtual
  79 priority range and map it to the interval given by
  80 .BR sched_get_priority_max ()
  81 and
  82 .BR sched_get_priority_min
  83 POSIX.1 requires
  84 .\" POSIX.1-2001, POSIX.1-2008 (XBD 2.8.4)
  85 a spread of at least 32 between the maximum and the minimum values for
  86 .B SCHED_FIFO
  87 and
  88 .BR SCHED_RR .
  89 .PP
  90 POSIX systems on which
  91 .BR sched_get_priority_max ()
  92 and
  93 .BR sched_get_priority_min ()
  94 are available define
  95 .B _POSIX_PRIORITY_SCHEDULING
  96 in
  97 .IR <unistd.h> .
  98 .SH RETURN VALUE
  99 On success,
 100 .BR sched_get_priority_max ()
 101 and
 102 .BR sched_get_priority_min ()
 103 return the maximum/minimum priority value for the named scheduling
 104 policy.
 105 On error, \-1 is returned, and
 106 .I errno
 107 is set appropriately.
 108 .SH ERRORS
 109 .TP
 110 .B EINVAL
 111 The argument
 112 .I policy
 113 does not identify a defined scheduling policy.
 114 .SH CONFORMING TO
 115 POSIX.1-2001, POSIX.1-2008.
 116 .SH SEE ALSO
 117 .ad l
 118 .nh
 119 .BR sched_getaffinity (2),
 120 .BR sched_getparam (2),
 121 .BR sched_getscheduler (2),
 122 .BR sched_setaffinity (2),
 123 .BR sched_setparam (2),
 124 .BR sched_setscheduler (2),
 125 .BR sched (7)