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 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
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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.
MASTER FILE
The ts_dptbl can be reconfigured at boot time by specifying the
desired values in the ts master file and reconfiguring the system
using the auto-configuration boot procedure; see mkboot(1M) and
master(4). 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 class.
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 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
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ts_dptbl(4) ts_dptbl(4)
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.
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
# 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
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ts_dptbl(4) ts_dptbl(4)
FILES
/usr/include/sys/ts.h
SEE ALSO
dispadmin(1M), priocntl(1), priocntl(2), master(4), mkboot(1M)
``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 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.
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