ts_dptbl(4) ts_dptbl(4)
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). (Time-sharing 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 of parameter
structures (struct ts_dpent), one for each of the n priority
levels used by time-sharing processes in user mode. The
properties of a given priority level i are specified by the
ith parameter structure in this array (ts_dptbli).
A parameter structure consists of the following members.
These are also described in the /usr/include/sys/ts.h header
file.
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
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ts_dptbl(4) ts_dptbl(4)
cannot be changed with dispadmin(1M).
ts_quantum
The length of the time quantum allocated to processes
at this level in ticks (HZ).
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 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 the dispatcher queue.
If a process's ts_dispwait value exceeds the
ts_maxwait value for its level, the process's 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. There
are two methods available for doing this.
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 class allows the administrator to retrieve the
current ts_dptbl configuration from the kernel's in-core
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ts_dptbl(4) ts_dptbl(4)
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
system clock's resolution is hardware-dependent; this
resolution can be calculated from the value of HZ, which is
defined in the file /usr/include/sys/param.h. HZ gives the
number of clock ticks per second of the system clock. For
example, an HZ of 100 specifies 100 clock ticks per second, or
one tick every 10 milliseconds (that is, this system clock has
a resolution of 10 milliseconds). If the -t and -r options
are used to specify a time quantum of 34 milliseconds, it is
rounded up to 4 ticks (40 milliseconds) on a machine with an
HZ of 100.
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, and so on. There must be exactly one line for each
configured time-sharing priority level.
EXAMPLE
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 class, 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
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ts_dptbl(4) ts_dptbl(4)
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
FILES
/usr/include/sys/ts.h
REFERENCES
dispadmin(1M), priocntl(1), priocntl(2)
NOTICES
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 master file. Specifying an inconsistent or nonsensical
ts_dptbl configuration through the ts master file could cause
serious performance problems and/or cause the system to panic.
Copyright 1994 Novell, Inc. Page 4