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)