File Formats rt_dptbl(4)
NAME
rt_dptbl - 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 theclass. 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 levelsnumbered 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 intomight 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 thatlevel. This table is called the real-time dispatcher parame-
ter table (rt_dptbl). The rt_dptbl consists of an array
(config_rt_dptbl[]) of parameter structures (struct
rtdpent_t), one for each of the n priority levels. The
structure are accessed via a pointer, (rt_dptbl), to the
array. The properties of a given priority level i are speci-
fied by the ith parameter structure in this array (rt_dptbl[i] ).
A parameter structure consists of the following members. These are also described in the /usr/include/sys/rt.h header file.rt_globpri The global scheduling priority associated with
this priority level. The rt_globpri values
cannot be changed with dispadmin(1M).rt_quantum The length of the time quantum allocated to
processes at this level in ticks (hz). Thetime quantum value is only a default or start-
ing value for processes at a particular levelas the time quantum of a real-time process can
be changed by the user with the priocntl com-
mand or the priocntl system call.SunOS 5.11 Last change: 15 Oct 2002 1
File Formats rt_dptbl(4)
In the high resolution clock mode (hires_tick
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 rt_dptbl.
There are two methods available for doing this: reconfigurewith a loadable module at boot-time or by using
dispadmin(1M) at run-time.
rt_dptbl Loadable Module
The rt_dptbl can be reconfigured with a loadable module
which contains a new real time dispatch table. The modulecontaining 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. Therelevant procedure and source code is described in the Exam-
ples section. dispadmin Configuration FileThe rt_quantum values in the rt_dptbl 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 rt_dptbl 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 rightof 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.SunOS 5.11 Last change: 15 Oct 2002 2
File Formats rt_dptbl(4)
The remaining lines in the file are used to specify thert_quantum 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 rt_quantum entry must be either a posi-
tive integer specifying the desired time quantum (in theresolution 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 withinthe 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 theRT_DPTBL 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 byconsecutive, 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; iffor some reason they don't, however, dispadmin is unaf-
fected.# 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
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Example 2 Replacing The rt_dptbl 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 yousave the existing module before using the following pro-
cedure. 1. Place the dispatch table code shown below in a filecalled rt_dptbl.c An example of an rt_dptbl.c file
follows. 2. Compile the code using the given compilation and link lines supplied.cc -c -0 -D_KERNEL rt_dptbl.c
ld -r -o RT_DPTBL rt_dptbl.o
3. Copy the current dispatch table in/usr/kernel/sched to RT_DPTBL.bak.
4. Replace the current RT_DPTBL in /usr/kernel/sched.
5. You will have to make changes in the /etc/system file to reflect the changes to the sizes of thetables. See system(4). The rt_maxpri variable may
need changing. The syntax for setting this is:set RT:rt_maxpri=(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 rt_dptbl.c file used for
building the new rt_dptbl.
/* BEGIN rt_dptbl.c */
#include
#include
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#include
#include
#include
#include
/* * This is the loadable module wrapper. */#include
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,SunOS 5.11 Last change: 15 Oct 2002 5
File Formats rt_dptbl(4)
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);
}SEE ALSO
priocntl(1), dispadmin(1M), priocntl(2), system(4)SunOS 5.11 Last change: 15 Oct 2002 6
File Formats rt_dptbl(4)
System Administration Guide: Basic Administration Programming Interfaces GuideSunOS 5.11 Last change: 15 Oct 2002 7