TS_DPTBL(5) File Formats and Configurations TS_DPTBL(5)

NAME

ts_dptbl - time-sharing 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 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 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
(depending on the configuration).


Processes in the time-sharing class which are running in user mode
(or in kernel mode before going to sleep) are scheduled according to
the parameters in a time-sharing dispatcher parameter table
(ts_dptbl). Processes in the inter-active scheduling class are also
scheduled according to the parameters in the time-sharing dispatcher
parameter table. (Time-sharing processes and inter-active processes
running in kernel mode after sleeping are run within a special range
of priorities reserved for such processes and are not affected by the
parameters in the ts_dptbl until they return to user mode.) The
ts_dptbl consists of an array (config_ts_dptbl[]) of parameter
structures (struct tsdpent_t), one for each of the n priority levels
used by time-sharing processes and inter-active processes in user
mode. The structures are accessed via a pointer, (ts_dptbl), to the
array. The properties of a given priority level i are specified by
the ith parameter structure in this array (ts_dptbl[i]).


A parameter structure consists of the following members. These are
also described in the /usr/include/sys/ts.h header.

ts_globpri
The global scheduling priority associated with this
priority level. The mapping between time-sharing
priority levels and global scheduling priorities is
determined at boot time by the system configuration.
ts_globpri is the only member of the ts_dptbl which
cannot be changed with dispadmin(8).


ts_quantum
The length of the time quantum allocated to processes
at this level in ticks (hz).

In the default high resolution clock mode (hires_tick
set to 1), the value of hz is set to 1000. If this
value is overridden to 0 then hz will instead be 100;
the number of ticks per quantum must then be decreased
to maintain the same length of quantum in absolute
time.


ts_tqexp
Priority level of the new queue on which to place a
process running at the current level if it exceeds its
time quantum. Normally this field links to a lower
priority time-sharing level that has a larger quantum.


ts_slpret
Priority level of the new queue on which to place a
process, that was previously in user mode at this
level, when it returns to user mode after sleeping.
Normally this field links to a higher priority level
that has a smaller quantum.


ts_maxwait
A per process counter, ts_dispwait is initialized to
zero each time a time-sharing or inter-active process
is placed back on the dispatcher queue after its time
quantum has expired or when it is awakened (ts_dispwait
is not reset to zero when a process is preempted by a
higher priority process). This counter is incremented
once per second for each process on a dispatcher or
sleep queue. If a process' ts_dispwait value exceeds
the ts_maxwait value for its level, the process'
priority is changed to that indicated by ts_lwait. The
purpose of this field is to prevent starvation.


ts_lwait
Move a process to this new priority level if
ts_dispwait is greater than ts_maxwait.


An administrator can affect the behavior of the time-sharing portion
of the scheduler by reconfiguring the ts_dptbl. Since processes in
the time-sharing and inter-active scheduling classes share the same
dispatch parameter table (ts_dptbl), changes to this table will
affect both scheduling classes. There are two methods available for
doing this: reconfigure with a loadable module at boot-time or by
using dispadmin(8) at run-time.

ts_dptbl Loadable Module
The ts_dptbl can be reconfigured with a loadable module which
contains a new time sharing dispatch table. The module containing the
dispatch table is separate from the TS loadable module which contains
the rest of the time-sharing and inter-active software. This is the
only method that can be used to change the number of time-sharing
priority levels or the set of global scheduling priorities used by
the time-sharing and inter-active classes. The relevant procedure and
source code is described in the REPLACING THE TS_DPTBL LOADABLE
MODULE section.

dispadmin Configuration File
With the exception of ts_globpri all of the members of the ts_dptbl
can be examined and modified on a running system using the
dispadmin(8) command. Invoking dispadmin for the time-sharing or
inter-active class allows the administrator to retrieve the current
ts_dptbl 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 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
ts_quantum 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.


The remaining lines in the file are used to specify the parameter
values for each of the time-sharing priority levels. The first line
specifies the parameters for time-sharing level 0, the second line
specifies the parameters for time-sharing level 1, etc. There must be
exactly one line for each configured time-sharing priority level.

EXAMPLES

Example 1: A Sample From a Configuration File

The following excerpt from a dispadmin configuration file illustrates
the format. Note that for each line specifying a set of parameters
there is a comment indicating the corresponding priority level. These
level numbers indicate priority within the time-sharing and
interactive classes, and the mapping between these time-sharing
priorities and the corresponding global scheduling priorities is
determined by the configuration specified in the ts master file. The
level numbers are strictly for the convenience of the administrator
reading the file and, as with any comment, they are ignored by
dispadmin. dispadmin assumes that the lines in the file are ordered
by consecutive, increasing priority level (from 0 to the maximum
configured time-sharing priority). The level numbers in the comments
should normally agree with this ordering; if for some reason they
don't, however, dispadmin is unaffected.


# Time-Sharing Dispatcher Configuration File RES=1000


# ts_quantum ts_tqexp ts_slpret ts_maxwait ts_lwait PRIORITY
# LEVEL
500 0 10 5 10 # 0
500 0 11 5 11 # 1
500 1 12 5 12 # 2
500 1 13 5 13 # 3
500 2 14 5 14 # 4
500 2 15 5 15 # 5
450 3 16 5 16 # 6
450 3 17 5 17 # 7
. . . . . . .
. . . . . . .
. . . . . . .
50 48 59 5 59 # 58
50 49 59 5 59 # 59

Example 2: Replacing The ts_dptbl Loadable Module

In order to change the size of the time sharing 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.


1. Place the dispatch table code shown below in a file called
ts_dptbl.c An example of this file follows.

2. Compile the code using the given compilation and link
lines supplied.

cc -c -0 -D_KERNEL
ts_dptbl.c
ld -r -o TS_DPTBL ts_dptbl.o


3. Copy the current dispatch table in /kernel/sched to
TS_DPTBL.bak.

4. Replace the current TS_DPTBL in /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(5). The two variables affected are ts_maxupri and
ts_maxkmdpri. The syntax for setting these is as follows:

set TS:ts_maxupri=(value for max time-sharing user priority)
set TS:ts_maxkmdpri=(number of kernel mode priorities - 1)


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 do not get it right, panics may result, thus making
the system unusable.


The following is an example of a ts_dptbl.c file used for building
the new ts_dptbl.


/* BEGIN ts_dptbl.c */
#include <sys/proc.h>
#include <sys/priocntl.h>
#include <sys/class.h>
#include <sys/disp.h>
#include <sys/ts.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, "Time sharing dispatch table"
};
static struct modlinkage modlinkage = {
MODREV_1, &modlmisc, 0
};
_init()
{
return (mod_install(&modlinkage));
}
_info(modinfop)
struct modinfo *modinfop;
{
return (mod_info(&modlinkage, modinfop));
}
/*
* array of global priorities used by ts procs sleeping or
* running in kernel mode after sleep. Must have at least
* 40 values.
*/
pri_t config_ts_kmdpris[] = {
60,61,62,63,64,65,66,67,68,69,
70,71,72,73,74,75,76,77,78,79,
80,81,82,83,84,85,86,87,88,89,
90,91,92,93,94,95,96,97,98,99,
};
tsdpent_t config_ts_dptbl[] = {

/* glbpri qntm tqexp slprt mxwt lwt */

0, 100, 0, 10, 5, 10,
1, 100, 0, 11, 5, 11,
2, 100, 1, 12, 5, 12,
3, 100, 1, 13, 5, 13,
4, 100, 2, 14, 5, 14
5, 100, 2, 15, 5, 15,
6, 100, 3, 16, 5, 16,
7, 100, 3, 17, 5, 17,
8, 100, 4, 18, 5, 18,
9, 100, 4, 19, 5, 19,
10, 80, 5, 20, 5, 20,
11, 80, 5, 21, 5, 21,
12, 80, 6, 22, 5, 22,
13, 80, 6, 23, 5, 23,
14, 80, 7, 24, 5, 24,
15, 80, 7, 25, 5, 25,
16, 80, 8, 26, 5, 26,
17, 80, 8, 27, 5, 27,
18, 80, 9, 28, 5, 28,
19, 80, 9, 29, 5, 29,
20, 60, 10, 30, 5, 30,
21, 60, 11, 31, 5, 31,
22, 60, 12, 32, 5, 33,
24, 60, 14, 34, 5, 34,
25, 60, 15, 35, 5, 35,
26, 60, 16, 36, 5, 36,
27, 60, 17, 37, 5, 37,
28, 60, 18, 38, 5, 38,
29, 60, 19, 39, 5, 39,
30, 40, 20, 40, 5, 40,
31, 40, 21, 41, 5, 41,
32, 40, 22, 42, 5, 42,
33, 40, 23, 43, 5, 43,
34, 40, 24, 44, 5, 44,
35, 40, 25, 45, 5, 45,
36, 40, 26, 46, 5, 46,
37, 40, 27, 47, 5, 47,
38, 40, 28, 48, 5, 48,
39, 40, 29, 49, 5, 49,
40, 20, 30, 50, 5, 50,
41, 20, 31, 50, 5, 50,
42, 20, 32, 51, 5, 51,
43, 20, 33, 51, 5, 51,
44, 20, 34, 52, 5, 52,
45, 20, 35, 52, 5, 52,
46, 20, 36, 53, 5, 53,
47, 20 37, 53, 5, 53,
48, 20, 38, 54, 5, 54,
49, 20, 39, 54, 5, 54,
50, 10, 40, 55, 5, 55,
51, 10, 41, 55, 5, 55,
52, 10, 42, 56, 5, 56,
53, 10, 43, 56, 5, 56,
54, 10, 44, 57, 5, 57,
55, 10, 45, 57, 5, 57,
56, 10, 46, 58, 5, 58,
57, 10, 47, 58, 5, 58,
58, 10, 48, 59, 5, 59,
59, 10, 49, 59, 5, 59,

};

short config_ts_maxumdpri = sizeof (config_ts_dptbl)/16 - 1;
/*
* Return the address of config_ts_dptbl
*/
tsdpent_t *
ts_getdptbl()
{
return (config_ts_dptbl);
}

/*
* Return the address of config_ts_kmdpris
*/
int *
ts_getkmdpris()
{
return (config_ts_kmdpris);
}

/*
* Return the address of ts_maxumdpri
*/
short
ts_getmaxumdpri()
{
return (config_ts_maxumdpri);
}

/* END ts_dptbl.c */

SEE ALSO

priocntl(1), priocntl(2), system(5), dispadmin(8)


System Administration Guide: Basic Administration


Programming Interfaces Guide

NOTES

dispadmin does some limited sanity checking on the values supplied in
the configuration file. The sanity checking is intended to ensure
that the new ts_dptbl values do not cause the system to panic. The
sanity checking does not attempt to analyze the effect that the new
values will have on the performance of the system. Unusual ts_dptbl
configurations may have a dramatic negative impact on the performance
of the system.


No sanity checking is done on the ts_dptbl values specified in the
TS_DPTBL loadable module. Specifying an inconsistent or nonsensical
ts_dptbl configuration through the TS_DPTBL loadable module could
cause serious performance problems and/or cause the system to panic.

February 17, 2023 TS_DPTBL(5)