File Formats rtdptbl(4)
NAME
rtdptbl - real-time dispatcher parameter table
DESCRIPTION
The process scheduler (or dispatcher) is the portion of the
kernel that controls allocation of the CPU 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 pro-
cess with the highest global scheduling priority in the sys-
tem. 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 n (highest priority-a
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, depend-
ing on the configuration.
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 parame-
ter table (rtdptbl). The rtdptbl consists of an array
(configrtdptbl[]) of parameter structures (struct
rtdpentt), one for each of the n priority levels. The
structure are accessed via a pointer, (rtdptbl), to the
array. The properties of a given priority level i are speci-
fied by the ith parameter structure in this array (
rtdptbl[i] ).
A parameter structure consists of the following members.
These are also described in the /usr/include/sys/rt.h header
file.
rtglobpri The global scheduling priority associated with
this priority level. The rtglobpri values
cannot be changed with dispadmin(1M).
rtquantum The length of the time quantum allocated to
processes at this level in ticks (hz). The
time quantum value is only a default or start-
ing value for processes at a particular level
as the time quantum of a real-time process can
be changed by the user with the priocntl com-
mand or the priocntl system call.
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In the high resolution clock mode (hirestick
set to 1), the value of hz is set to 1000.
Increase quantums to maintain the same abso-
lute time quantums.
An administrator can affect the behavior of the real-time
portion of the scheduler by reconfiguring the rtdptbl.
There are two methods available for doing this: reconfigure
with a loadable module at boot-time or by using
dispadmin(1M) at run-time.
rtdptbl Loadable Module
The rtdptbl 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 load-
able 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 Exam-
ples section.
dispadmin Configuration File
The rtquantum values in the rtdptbl can be examined and
modified on a running system using the dispadmin(1M) com-
mand. Invoking dispadmin for the real-time class allows the
administrator to retrieve the current rtdptbl configuration
from the kernel's in-core table, or overwrite the in-core
table with values from a configuration file. The configura-
tion file used for input to dispadmin must conform to the
specific format described below.
Blank lines are ignored and any part of a line to the right
of a # 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
RES=res
where res is a positive integer between 1 and 1,000,000,000
inclusive and the resolution used is the reciprocal of res
in seconds. (For example, RES=1000 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.
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The remaining lines in the file are used to specify the
rtquantum 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 rtquantum entry must be either a posi-
tive integer specifying the desired time quantum (in the
resolution given by res), or the value -2 indicating an
infinite time quantum for that level.
EXAMPLES
Example 1 A Sample dispadmin Configuration File
The following excerpt from a dispadmin 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 priori-
ties is determined by the configuration specified in the
RTDPTBL 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 dispadmin on input.
dispadmin assumes that the lines in the file are ordered by
consecutive, increasing priority level (from 0 to the max-
imum configured real-time priority). The level numbers in
the comments should normally agree with this ordering; if
for some reason they don't, however, dispadmin is unaf-
fected.
# Real-Time Dispatcher Configuration File
RES=1000
# TIME QUANTUM PRIORITY
# (rtquantum)LEVEL
100# 0
100# 1
100# 2
100# 3
100# 4
100# 5
90 # 6
90 # 7
.. .
.. .
.. .
10# 58
10# 59
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Example 2 Replacing The rtdptbl Loadable Module
In order to change the size of the real time dispatch table,
the loadable module which contains the dispatch table infor-
mation will have to be built. It is recommended that you
save the existing module before using the following pro-
cedure.
1. Place the dispatch table code shown below in a file
called rtdptbl.c An example of an rtdptbl.c file
follows.
2. Compile the code using the given compilation and
link lines supplied.
cc -c -0 -DKERNEL rtdptbl.c
ld -r -o RTDPTBL rtdptbl.o
3. Copy the current dispatch table in
/usr/kernel/sched to RTDPTBL.bak.
4. Replace the current RTDPTBL in /usr/kernel/sched.
5. You will have to make changes in the /etc/system
file to reflect the changes to the sizes of the
tables. See system(4). The rtmaxpri variable may
need changing. The syntax for setting this is:
set RT:rtmaxpri=(class-specific value for maximum \
real-time priority)
6. Reboot the system to use the new dispatch table.
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.
The following is an example of a rtdptbl.c file used for
building the new rtdptbl.
/* BEGIN rtdptbl.c */
#include
#include
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#include
#include
#include
#include
/*
* This is the loadable module wrapper.
*/
#include
extern struct modops modmiscops;
/*
* Module linkage information for the kernel.
*/
static struct modlmisc modlmisc = {
&modmiscops, "realtime dispatch table"
};
static struct modlinkage modlinkage = {
MODREV1, &modlmisc, 0
};
init()
{
return (modinstall(&modlinkage));
}
info (struct modinfo *modinfop)
{
return (modinfo(&modlinkage, modinfop));
}
rtdpentt configrtdptbl[] = {
/* 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,
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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 configrtdptbl
*/ rtdpentt *
rtgetdptbl()
{
return (configrtdptbl);
}
SEE ALSO
priocntl(1), dispadmin(1M), priocntl(2), system(4)
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System Administration Guide: Basic Administration
Programming Interfaces Guide
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