'\"macro stdmacro
.if n .pH g4.ts_dptbl @(#)ts_dptbl	40.11 of 10/10/89
.\" Copyright 1989 AT&T
.nr X
.if \nX=0 .ds x} ts_dptbl 4 "" "\&"
.if \nX=1 .ds x} ts_dptbl 4 ""
.if \nX=2 .ds x} ts_dptbl 4 "" "\&"
.if \nX=3 .ds x} ts_dptbl "" "" "\&"
.TH \*(x}
.SH NAME
\f4ts_dptbl\f1 \- time-sharing dispatcher parameter table
.SH DESCRIPTION
The process scheduler (or dispatcher) is the portion of the kernel that
controls allocation of the
.SM 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 \f2n\f1 (highest priority\(ema
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).
.P
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
(\f4ts_dptbl\f1).
(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 \f4ts_dptbl\f1 until they
return to user mode.)
The \f4ts_dptbl\f1 consists of an array of parameter structures
(\f4struct ts_dpent\f1), one for each of the \f2n\f1 priority levels
used by time-sharing processes in user mode.
The properties of a given priority level \f2i\f1 are specified
by the \f2i\f1th parameter structure in this array (\f4ts_dptbl\f2i\f1).
.P
A parameter structure consists of the following members.
These are also described in the \f4/usr/include/sys/ts.h\f1
header file.
.TP 8m
\f4ts_globpri\f1
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.
\f4ts_globpri\f1 is the only member of the \f4ts_dptbl\fP which
cannot be changed with \f4dispadmin\fP(1M).
.TP 8m
\f4ts_quantum\f1
The length of the time quantum allocated to processes at this level in ticks
(HZ).
.TP 8m
\f4ts_tqexp\f1
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.
.TP 8m
\f4ts_slpret\f1
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.
.TP 8m
\f4ts_maxwait\f1
A per process counter, \f4ts_dispwait\f1 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 (\f4ts_dispwait\f1 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 \f4ts_dispwait\f1 value exceeds the \f4ts_maxwait\f1 value
for its level, the process's priority
is changed to that indicated by \f4ts_lwait\f1.
The purpose of this field is to prevent starvation.
.TP 8m
\f4ts_lwait\f1
Move a process to this new priority level if \f4ts_dispwait\f1 is greater than
\f4ts_maxwait\f1.
.PP
An administrator can affect the behavior of the time-sharing
portion of the scheduler by reconfiguring the \f4ts_dptbl\fP.
There are two methods available for doing this.
.SH MASTER FILE
The \f4ts_dptbl\fP can be reconfigured at boot time by specifying the
desired values in the \f4ts\f1 master file and reconfiguring the system
using the auto-configuration boot procedure; see \f4mkboot\fP(1M) and
\f4master\fP(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.
.SH DISPADMIN CONFIGURATION FILE
With the exception of \f4ts_globpri\f1 all of the members of the \f4ts_dptbl\fP
can be examined and modified on a running system
using the \f4dispadmin\fP(1M) command.
Invoking \f4dispadmin\fP for the time-sharing class allows the
administrator to retrieve the current \f4ts_dptbl\fP 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 \f4dispadmin\fP must conform
to the specific format described below.
.P
Blank lines are ignored and any part of a line to the right of a \f2#\f1
symbol is treated as a comment.
The first non-blank, non-comment line must indicate the resolution to be
used for interpreting the \f4ts_quantum\f1 time quantum values.
The resolution is specified as
.P
.RS
\f4RES=\f2res\f1
.RE
.P
where \f2res\f1 is a positive integer between 1 and 1,000,000,000 inclusive
and the resolution used is the reciprocal of \f2res\f1 in seconds
(for example, \f4RES=1000\f1 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 \f2res\f1 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.
.P
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.
.SH EXAMPLE
The following excerpt from a \f4dispadmin\fP 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 \f4ts\f1 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 \f4dispadmin\fP.
\f4dispadmin\fP 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, \f4dispadmin\fP is unaffected.
.P
.ft 4
.nf
# 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
.fi
.ft 1
.SH FILES
.nf
\f4/usr/include/sys/ts.h\f1
.fi
.SH SEE ALSO
\f4dispadmin\f1(1M), \f4priocntl\f1(1), \f4priocntl\f1(2), \f4master\f1(4), \f4mkboot\f1(1M)
.P
``Scheduler'' chapter in the
.I "System Administrator's Guide"
.SH NOTES
\f4dispadmin\fP does some limited sanity checking on the values
supplied in the configuration file.
The sanity checking is intended to ensure that the new \f4ts_dptbl\fP
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 \f4ts_dptbl\fP configurations may have a dramatic negative impact
on the performance of the system.
.P
No sanity checking is done on the \f4ts_dptbl\fP values specified
in the \f4ts\f1 master file.
Specifying an inconsistent or nonsensical \f4ts_dptbl\fP configuration
through the \f4ts\f1 master file could cause serious performance problems
and/or cause the system to panic.
.Ee
