ts_dptbl(4) UNIX System V ts_dptbl(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 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 (tsdptbl).
(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 tsdptbl until they return to user
mode.) The tsdptbl consists of an array of parameter structures (struct
tsdpent), 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 (tsdptbli).
A parameter structure consists of the following members. These are also
described in the /usr/include/sys/ts.h header file.
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 time by the
system configuration. tsglobpri is the only member of the
tsdptbl which cannot be changed with dispadmin(1M).
tsquantum
The length of the time quantum allocated to processes at this
level in ticks (HZ).
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.
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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 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
(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 the dispatcher queue. If a process's
tsdispwait value exceeds the tsmaxwait value for its level, the
process's priority is changed to that indicated by tslwait. The
purpose of this field is to prevent starvation.
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. There are two methods
available for doing this.
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 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 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. For example, the finest resolution currently available on
the 3B2 is 10 milliseconds (1 ``tick''). If res were 1000 a time quantum
value of 34 would specify a quantum of 34 milliseconds, which would be
rounded up to 4 ticks (40 milliseconds) on the 3B2.
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ts_dptbl(4) UNIX System V ts_dptbl(4)
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.
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 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
FILES
/usr/include/sys/ts.h
SEE ALSO
dispadmin(1M), priocntl(1), priocntl(2),
``Scheduler'' chapter in the System Administrator's 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
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have on the performance 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 ts
master file. Specifying an inconsistent or nonsensical tsdptbl
configuration through the ts master file could cause serious performance
problems and/or cause the system to panic.
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