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 2006-03-23 "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 .sp
  35 .BI "int sched_get_priority_max(int " policy );
  36 .sp
  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 \fIpolicy\fP.
  42 .BR sched_get_priority_min ()
  43 returns the minimum priority value that can be used with the
  44 scheduling algorithm identified by \fIpolicy\fP.
  45 Supported \fIpolicy\fP
  46 values are
  47 .BR SCHED_FIFO ,
  48 .BR SCHED_RR ,
  49 .BR SCHED_OTHER ,
  50 and
  51 .BR SCHED_BATCH .
  52 Further details about these policies can be found in
  53 .BR sched_setscheduler (2).
  54
  55 Processes with numerically higher priority values are scheduled before
  56 processes with numerically lower priority values.
  57 Thus, the value
  58 returned by
  59 .BR sched_get_priority_max ()
  60 will be greater than the
  61 value returned by
  62 .BR sched_get_priority_min ().
  63
  64 Linux allows the static priority value range 1 to 99 for
  65 \fBSCHED_FIFO\fP and \fBSCHED_RR\fP and the priority 0 for
  66 \fBSCHED_OTHER\fP and \fBSCHED_BATCH\fP.
  67 Scheduling priority ranges for the various policies
  68 are not alterable.
  69
  70 The range of scheduling priorities may vary on other POSIX systems,
  71 thus it is a good idea for portable applications to use a virtual
  72 priority range and map it to the interval given by
  73 .BR sched_get_priority_max ()
  74 and
  75 .BR sched_get_priority_min ().
  76 POSIX.1-2001 requires a spread of at least 32 between the maximum and the
  77 minimum values for \fBSCHED_FIFO\fP and \fBSCHED_RR\fP.
  78
  79 POSIX systems on which
  80 .BR sched_get_priority_max ()
  81 and
  82 .BR sched_get_priority_min ()
  83 are available define
  84 .B _POSIX_PRIORITY_SCHEDULING
  85 in \fI<unistd.h>\fP.
  86 .SH RETURN VALUE
  87 On success,
  88 .BR sched_get_priority_max ()
  89 and
  90 .BR sched_get_priority_min ()
  91 return the maximum/minimum priority value for the named scheduling
  92 policy.
  93 On error, \-1 is returned, and
  94 .I errno
  95 is set appropriately.
  96 .SH ERRORS
  97 .TP
  98 .B EINVAL
  99 The argument \fIpolicy\fP does not identify a defined scheduling policy.
 100 .SH CONFORMING TO
 101 POSIX.1-2001.
 102 .SH SEE ALSO
 103 .ad l
 104 .nh
 105 .BR sched_getaffinity (2),
 106 .BR sched_getparam (2),
 107 .BR sched_getscheduler (2),
 108 .BR sched_setaffinity (2),
 109 .BR sched_setparam (2),
 110 .BR sched_setscheduler (2)
 111 .PP
 112 .I Programming for the real world \- POSIX.4
 113 by Bill O. Gallmeister, O'Reilly & Associates, Inc., ISBN 1-56592-074-0.