TS_DPTBL(4)TS_DPTBL(4)NAMEts_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 pol‐
icy, used to schedule processes within that class. Associated with each
scheduling class is a set of priority queues on which ready to run pro‐
cesses are linked. These priority queues are mapped by the system con‐
figuration into a set of global scheduling priorities which are avail‐
able 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-depen‐
dent 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 tsd‐
pent_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 pri‐
ority 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(1M).
ts_quantum
The length of the time quantum allocated to processes at
this level in ticks (hz).
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 absolute time quantums.
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 prior‐
ity 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 quan‐
tum 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 dis‐
patch 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 dis‐
padmin(1M) 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(1M)
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 # sym‐
bol 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 exam‐
ple, 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 resolu‐
tion.
The remaining lines in the file are used to specify the parameter val‐
ues for each of the time-sharing priority levels. The first line speci‐
fies 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 config‐
uration 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 sys‐
tem(4). 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 ALSOpriocntl(1), dispadmin(1M), priocntl(2), system(4)
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 configura‐
tions 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.
Oct 15, 2002 TS_DPTBL(4)
