fixed class dispatcher parameter table
The process scheduler (or dispatcher) is the portion of the kernel that
controls allocation of the
The scheduler supports the notion of scheduling classes where each
class defines a scheduling policy, used to schedule processes
Associated with each scheduling class is a set of priority queues on
which ready to run processes
These priority queues are mapped by the system configuration into a set
of global scheduling priorities which are available to processes
(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
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).
in the fixed class that are
running in user mode (or in kernel mode
before going to sleep) are scheduled according to the parameters in
a fixed class dispatcher parameter table
(Fixed class 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 fc_dptbl until they
return to user mode.)
The fc_dptbl consists of an array of parameter structures
(struct fcdpent), one for each of the n priority levels
used by fixed class processes in user mode.
The properties of a given priority level i are specified
by the ith parameter structure in this array (fc_dptbli).
A parameter structure consists of the following members.
These are also described in the /usr/include/sys/fc.h
The global scheduling priority associated with this priority level.
The mapping between fixed class priority levels and
global scheduling priorities is determined at boot time
by the system configuration.
fc_globpri is the only member of the fc_dptbl which
cannot be changed with
The length of the time quantum allocated to processes at this level in ticks
An administrator can affect the behavior of the fixed class
portion of the scheduler by reconfiguring the fc_dptbl.
There are two methods available for doing this.
With the exception of fc_globpri all of the members of the fc_dptbl
can be examined and modified on a running system
Invoking dispadmin for the fixed class class allows the
administrator to retrieve the current fc_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 fc_quantum time quantum values.
The resolution is specified as
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
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 fixed class priority levels.
The first line specifies the parameters for fixed class level 0, the
second line specifies the parameters for fixed class level 1, and so on.
There must be exactly one line for each configured fixed class
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 fixed class class,
and the mapping between these fixed class priorities and the corresponding
global scheduling priorities is determined by the configuration specified
in the fc 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
fixed class priority).
The level numbers in the comments should normally agree with this ordering;
if for some reason they don't, however, dispadmin is unaffected.
# Fixed Class Dispatcher Configuration
# fc_quantum PRIORITY LEVEL
500 # 0
500 # 1
500 # 2
500 # 3
500 # 4
500 # 5
450 # 6
450 # 7
. . .
. . .
. . .
50 # 58
50 # 59
dispadmin does some limited sanity checking on the values
supplied in the configuration file.
The sanity checking is intended to ensure that the new fc_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 fc_dptbl configurations may have a dramatic negative impact
on the performance of the system.
No sanity checking is done on the fc_dptbl values specified
in the ts master file.
Specifying an inconsistent or nonsensical fc_dptbl configuration
through the ts master file could cause serious performance problems
and/or cause the system to panic.
© 2004 The SCO Group, Inc. All rights reserved.
UnixWare 7 Release 7.1.4 - 25 April 2004