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.TH RT_DPTBL 4 "Oct 15, 2002"
.SH NAME
rt_dptbl \- real-time dispatcher parameter table
.SH DESCRIPTION
.sp
.LP
The process scheduler (or dispatcher) is the portion of the kernel that
controls allocation of the \fBCPU\fR to processes. The scheduler supports the
notion of scheduling classes where each class defines a scheduling policy, used
to schedule processes within that class. Associated with each scheduling class
is a set of priority queues on which ready to run processes are linked. These
priority queues are mapped by the system configuration into a set of global
scheduling priorities which are available to processes within the class. The
dispatcher always selects for execution the process with the highest global
scheduling priority in the system. The priority queues associated with a given
class are viewed by that class as a contiguous set of priority levels numbered
from 0 (lowest priority) to \fIn\fR (highest priority\(ema configuration
dependent value). The set of global scheduling priorities that the queues for a
given class are mapped into might not start at zero and might not be
contiguous, depending on the configuration.
.sp
.LP
The real-time class maintains an in-core table, with an entry for each priority
level, giving the properties of that level. This table is called the real-time
dispatcher parameter table (\fBrt_dptbl\fR). The \fBrt_dptbl\fR consists of an
array (\fBconfig_rt_dptbl[]\fR) of parameter structures (\fBstruct
rtdpent_t\fR), one for each of the \fIn\fR priority levels. The structure are
accessed via a pointer, (\fBrt_dptbl\fR), to the array. The properties of a
given priority level \fIi\fR are specified by the \fIi\fRth parameter structure
in this array ( \fBrt_dptbl[\fR\fIi\fR\fB]\fR ).
.sp
.LP
A parameter structure consists of the following members. These are also
described in the \fB/usr/include/sys/rt.h\fR header file.
.sp
.ne 2
.na
\fB\fBrt_globpri\fR\fR
.ad
.RS 14n
The global scheduling priority associated with this priority level. The
\fBrt_globpri\fR values cannot be changed with \fBdispadmin\fR(8).
.RE

.sp
.ne 2
.na
\fB\fBrt_quantum\fR\fR
.ad
.RS 14n
The length of the time quantum allocated to processes at this level in ticks
(\fBhz\fR). The time quantum value is only a default or starting value for
processes at a particular level as the time quantum of a real-time process can
be changed by the user with the \fBpriocntl\fR command or the \fBpriocntl\fR
system call.
.sp
In the high resolution clock mode (\fBhires_tick\fR set to \fB1\fR), the value
of \fBhz\fR is set to \fB1000\fR. Increase quantums to maintain the same
absolute time quantums.
.RE

.sp
.LP
An administrator can affect the behavior of the real-time portion of the
scheduler by reconfiguring the \fBrt_dptbl\fR. There are two methods available
for doing this: reconfigure with a loadable module at boot-time or by using
\fBdispadmin\fR(8) at run-time.
.SS "rt_dptbl Loadable Module"
.sp
.LP
The \fBrt_dptbl\fR can be reconfigured with a loadable module which contains a
new real time dispatch table. The module containing the dispatch table is
separate from the RT loadable module which contains the rest of the real time
software. This is the only method that can be used to change the number of real
time priority levels or the set of global scheduling priorities used by the
real time class. The relevant procedure and source code is described in the
Examples section.
.SS "dispadmin Configuration File"
.sp
.LP
The \fBrt_quantum\fR values in the \fBrt_dptbl\fR can be examined and modified
on a running system using the \fBdispadmin\fR(8) command. Invoking
\fBdispadmin\fR for the real-time class allows the administrator to retrieve
the current \fBrt_dptbl\fR configuration from the kernel's in-core table, or
overwrite the in-core table with values from a configuration file. The
configuration file used for input to \fBdispadmin\fR must conform to the
specific format described below.
.sp
.LP
Blank lines are ignored and any part of a line to the right of a \fI#\fR symbol
is treated as a comment. The first non-blank, non-comment line must indicate
the resolution to be used for interpreting the time quantum values. The
resolution is specified as
.sp
.in +2
.nf
RES=\fIres\fR
.fi
.in -2

.sp
.LP
where \fIres\fR is a positive integer between 1 and 1,000,000,000 inclusive and
the resolution used is the reciprocal of \fIres\fR in seconds. (For example,
\fBRES=1000\fR specifies millisecond resolution.) Although very fine
(nanosecond) resolution may be specified, the time quantum lengths are rounded
up to the next integral multiple of the system clock's resolution.
.sp
.LP
The remaining lines in the file are used to specify the \fBrt_quantum\fR values
for each of the real-time priority levels. The first line specifies the quantum
for real-time level 0, the second line specifies the quantum for real-time
level 1. There must be exactly one line for each configured real-time priority
level. Each \fBrt_quantum\fR entry must be either a positive integer specifying
the desired time quantum (in the resolution given by \fIres\fR), or the value
-2 indicating an infinite time quantum for that level.
.SH EXAMPLES
.LP
\fBExample 1 \fRA Sample \fBdispadmin\fR Configuration File
.sp
.LP
The following excerpt from a \fBdispadmin\fR configuration file illustrates the
format. Note that for each line specifying a time quantum there is a comment
indicating the corresponding priority level. These level numbers indicate
priority within the real-time class, and the mapping between these real-time
priorities and the corresponding global scheduling priorities is determined by
the configuration specified in the \fBRT_DPTBL\fR loadable module. The level
numbers are strictly for the convenience of the administrator reading the file
and, as with any comment, they are ignored by \fBdispadmin\fR on input.
\fBdispadmin\fR assumes that the lines in the file are ordered by consecutive,
increasing priority level (from 0 to the maximum configured real-time
priority). The level numbers in the comments should normally agree with this
ordering; if for some reason they don't, however, \fBdispadmin\fR is
unaffected.

.sp
.in +2
.nf
# Real-Time Dispatcher Configuration File
RES=1000

# TIME QUANTUM PRIORITY
# (rt_quantum)LEVEL
100#   0
100#   1
100#   2
100#   3
100#   4
100#   5
90 #   6
90 #   7
\&..    .
\&..    .
\&..    .
10#   58
10#   59
.fi
.in -2

.LP
\fBExample 2 \fRReplacing The rt_dptbl Loadable Module
.sp
.LP
In order to change the size of the real time dispatch table, the loadable
module which contains the dispatch table information will have to be built. It
is recommended that you save the existing module before using the following
procedure.

.RS +4
.TP
1.
Place the dispatch table code shown below in a file called \fBrt_dptbl.c\fR
An example of an \fBrt_dptbl.c\fR file follows.
.RE
.RS +4
.TP
2.
Compile the code using the given compilation and link lines supplied.
.sp
.in +2
.nf
cc -c -0 -D_KERNEL rt_dptbl.c
ld -r -o RT_DPTBL rt_dptbl.o
.fi
.in -2
.sp

.RE
.RS +4
.TP
3.
Copy the current dispatch table in \fB/usr/kernel/sched\fR to
\fBRT_DPTBL.bak\fR.
.RE
.RS +4
.TP
4.
Replace the current \fBRT_DPTBL\fR in \fB/usr/kernel/sched\fR.
.RE
.RS +4
.TP
5.
You will have to make changes in the \fB/etc/system\fR file to reflect the
changes to the sizes of the tables. See \fBsystem\fR(4). The \fBrt_maxpri\fR
variable may need changing. The syntax for setting this is:
.sp
.in +2
.nf
set RT:rt_maxpri=(class-specific value for maximum \e
        real-time priority)
.fi
.in -2

.RE
.RS +4
.TP
6.
Reboot the system to use the new dispatch table.
.RE
.sp
.LP
Great care should be used in replacing the dispatch table using this method. If
you don't get it right, the system may not behave properly.

.sp
.LP
The following is an example of a \fBrt_dptbl.c\fR file used for building the
new \fBrt_dptbl\fR.

.sp
.in +2
.nf
/*  BEGIN rt_dptbl.c  */
#include <sys/proc.h>
#include <sys/priocntl.h>
#include <sys/class.h>
#include <sys/disp.h>
#include <sys/rt.h>
#include <sys/rtpriocntl.h>
/*
 * This is the loadable module wrapper.
 */
#include <sys/modctl.h>
extern struct mod_ops mod_miscops;
/*
 * Module linkage information for the kernel.
 */
static struct modlmisc modlmisc = {
        &mod_miscops, "realtime dispatch table"
};
static struct modlinkage modlinkage = {
        MODREV_1, &modlmisc, 0
};
_init()
{
        return (mod_install(&modlinkage));
}
_info (struct modinfo *modinfop)
{
        return (mod_info(&modlinkage, modinfop));
}
rtdpent_t       config_rt_dptbl[] = {

/*   prilevel Time quantum  */

100,100,
101,100,
102,100,
103,100,
104,100,
105,100,
106,100,
107,100,
108,100,
109,100,
110,80,
111,80,
112,80,
113,80,
114,80,
115,80,
116,80,
117,80,
118,80,
119,80,
120,60,
121,60,
122,60,
123,60,
124,60,
125,60,
126,60,
127,60,
128,60,
129,60,
130,40,
131,40,
132,40,
133,40,
134,40,
135,40,
136,40,
137,40,
138,40,
139,40,
140,20,
141,20,
142,20,
143,20,
144,20,
145,20,
146,20,
147,20,
148,20,
149,20,
150,10,
151,10,
152,10,
153,10,
154,10,
155,10,
156,10,
157,10,
158,10,
159,10,

};
/*
 * Return the address of config_rt_dptbl
 */ rtdpent_t *
    rt_getdptbl()
{
           return (config_rt_dptbl);
}
.fi
.in -2

.SH SEE ALSO
.sp
.LP
\fBpriocntl\fR(1), \fBdispadmin\fR(8), \fBpriocntl\fR(2), \fBsystem\fR(4)
.sp
.LP
\fISystem Administration Guide: Basic Administration\fR
.sp
.LP
 \fIProgramming Interfaces Guide\fR