man-pages/man2/sched_get_priority_max.2

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.\" 1996-04-01 Tom Bjorkholm <tomb@mydata.se>
.\"            First version written
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.TH GET_PRIORITY_MAX 2 2006-03-23 "Linux 2.6.16" "Linux Programmer's Manual"
.SH NAME
sched_get_priority_max, sched_get_priority_min  \- get static priority range
.SH SYNOPSIS
.B #include <sched.h>
.sp
\fBint sched_get_priority_max(int \fIpolicy\fB);
.sp
\fBint sched_get_priority_min(int \fIpolicy\fB);
.fi
.SH DESCRIPTION
.BR sched_get_priority_max ()
returns the maximum priority value that can be used with the
scheduling algorithm identified by \fIpolicy\fR.
.BR sched_get_priority_min ()
returns the minimum priority value that can be used with the
scheduling algorithm identified by \fIpolicy\fR. Supported \fIpolicy\fR 
values are
.IR SCHED_FIFO , 
.IR SCHED_RR ,
.IR SCHED_OTHER ,
and 
.IR SCHED_BATCH .
Further details about these policies can be found in
.BR sched_setscheduler (2).

Processes with numerically higher priority values are scheduled before
processes with numerically lower priority values. Thus, the value
returned by \fBsched_get_priority_max\fR() will be greater than the
value returned by \fBsched_get_priority_min\fR().

Linux allows the static priority value range 1 to 99 for
\fISCHED_FIFO\fR and \fISCHED_RR\fR and the priority 0 for
\fISCHED_OTHER\fR and \fISCHED_BATCH\fP. 
Scheduling priority ranges for the various policies
are not alterable.

The range of scheduling priorities may vary on other POSIX systems,
thus it is a good idea for portable applications to use a virtual
priority range and map it to the interval given by
\fBsched_get_priority_max\fR() and \fBsched_get_priority_min\fR().
POSIX.1-2001 requires a spread of at least 32 between the maximum and the
minimum values for \fISCHED_FIFO\fR and \fISCHED_RR\fR.

POSIX systems on which
.BR sched_get_priority_max ()
and
.BR sched_get_priority_min ()
are available define
.I _POSIX_PRIORITY_SCHEDULING
in <unistd.h>.
.SH "RETURN VALUE"
On success,
.BR sched_get_priority_max ()
and
.BR sched_get_priority_min ()
return the maximum/minimum priority value for the named scheduling
policy.
On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
.TP
.B EINVAL
The parameter \fIpolicy\fR does not identify a defined scheduling policy.
.SH "CONFORMING TO"
POSIX.1-2001.
.SH "SEE ALSO"
.BR sched_getaffinity (2),
.BR sched_getparam (2),
.BR sched_getscheduler (2),
.BR sched_setaffinity (2),
.BR sched_setparam (2),
.BR sched_setscheduler (2)
.PP
.I Programming for the real world \- POSIX.4
by Bill O. Gallmeister, O'Reilly & Associates, Inc., ISBN 1-56592-074-0