File Formats tsdptbl(4)
NAME
tsdptbl - 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 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).
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 (tsdptbl). 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 spe-
cial range of priorities reserved for such processes and are
not affected by the parameters in the tsdptbl until they
return to user mode.) The tsdptbl consists of an array
(configtsdptbl[]) of parameter structures (struct
tsdpentt), 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, (tsdptbl),
to the array. The properties of a given priority level i are
specified by the ith parameter structure in this array
(tsdptbl[ i] ).
A parameter structure consists of the following members.
These are also described in the /usr/include/sys/ts.h
header.
tsglobpri The global scheduling priority associated with
this priority level. The mapping between
time-sharing priority levels and global
scheduling priorities is determined at boot
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File Formats tsdptbl(4)
time by the system configuration. tsglobpri
is the only member of the tsdptbl which can-
not be changed with dispadmin(1M).
tsquantum The length of the time quantum allocated to
processes at this level in ticks (hz).
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.
tstqexp 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.
tsslpret 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.
tsmaxwait A per process counter, tsdispwait is initial-
ized 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 (tsdispwait 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'
tsdispwait value exceeds the tsmaxwait value
for its level, the process' priority is
changed to that indicated by tslwait. The
purpose of this field is to prevent starva-
tion.
tslwait Move a process to this new priority level if
tsdispwait is greater than tsmaxwait.
An administrator can affect the behavior of the time-sharing
portion of the scheduler by reconfiguring the tsdptbl.
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Since processes in the time-sharing and inter-active
scheduling classes share the same dispatch parameter table
(tsdptbl), changes to this table will affect both schedul-
ing classes. There are two methods available for doing this:
reconfigure with a loadable module at boot-time or by using
dispadmin(1M) at run-time.
tsdptbl Loadable Module
The tsdptbl 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 load-
able 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 TSDPTBL LOAD-
ABLE MODULE section.
dispadmin Configuration File
With the exception of tsglobpri all of the members of the
tsdptbl 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 tsdptbl 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 tsquantum time quantum values. The resolu-
tion 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 lev-
els. The first line specifies the parameters for time-
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File Formats tsdptbl(4)
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
# tsquantum tstqexp tsslpret tsmaxwait tslwait 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 tsdptbl 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
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File Formats tsdptbl(4)
you save the existing module before using the following pro-
cedure.
1. Place the dispatch table code shown below in a file
called tsdptbl.c An example of this file follows.
2. Compile the code using the given compilation and
link lines supplied.
cc -c -0 -DKERNEL
tsdptbl.c
ld -r -o TSDPTBL tsdptbl.o
3. Copy the current dispatch table in /kernel/sched to
TSDPTBL.bak.
4. Replace the current TSDPTBL 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(4). The two variables affected
are tsmaxupri and tsmaxkmdpri. The syntax for
setting these is as follows:
set TS:tsmaxupri=(value for max time-sharing user priority)
set TS:tsmaxkmdpri=(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 tsdptbl.c file used for
building the new tsdptbl.
/* BEGIN tsdptbl.c */
#include
#include
#include
#include
#include
#include
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File Formats tsdptbl(4)
/*
* This is the loadable module wrapper.
*/
#include
extern struct modops modmiscops;
/*
* Module linkage information for the kernel.
*/
static struct modlmisc modlmisc = {
&modmiscops, "Time sharing dispatch table"
};
static struct modlinkage modlinkage = {
MODREV1, &modlmisc, 0
};
init()
{
return (modinstall(&modlinkage));
}
info(modinfop)
struct modinfo *modinfop;
{
return (modinfo(&modlinkage, modinfop));
}
/*
* array of global priorities used by ts procs sleeping or
* running in kernel mode after sleep. Must have at least
* 40 values.
*/
prit configtskmdpris[] = {
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,
};
tsdpentt configtsdptbl[] = {
/* 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,
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File Formats tsdptbl(4)
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 configtsmaxumdpri = sizeof (configtsdptbl)/16 - 1;
/*
* Return the address of configtsdptbl
*/
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File Formats tsdptbl(4)
tsdpentt *
tsgetdptbl()
{
return (configtsdptbl);
}
/*
* Return the address of configtskmdpris
*/
int *
tsgetkmdpris()
{
return (configtskmdpris);
}
/*
* Return the address of tsmaxumdpri
*/
short
tsgetmaxumdpri()
{
return (configtsmaxumdpri);
}
/* END tsdptbl.c */
SEE ALSO
priocntl(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 tsdptbl 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 per-
formance of the system. Unusual tsdptbl configurations may
have a dramatic negative impact on the performance of the
system.
No sanity checking is done on the tsdptbl values specified
in the TSDPTBL loadable module. Specifying an inconsistent
or nonsensical tsdptbl configuration through the TSDPTBL
loadable module could cause serious performance problems
and/or cause the system to panic.
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