fc_dptbl(4) fc_dptbl(4)
NAME
fc_dptbl - fixed class 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 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
(fc_dptbl). (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 header
file.
fc_globpri
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
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fc_dptbl(4) fc_dptbl(4)
cannot be changed with dispadmin(1M).
fc_quantum
The length of the time quantum allocated to processes
at this level in ticks (HZ).
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.
DISPADMIN CONFIGURATION FILE
With the exception of fc_globpri all of the members of the
fc_dptbl can be examined and modified on a running system
using the dispadmin(1M) command. 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
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.
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fc_dptbl(4) fc_dptbl(4)
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 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 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
RES=1000
# fc_quantum PRIORITY LEVEL
500 # 0
500 # 1
500 # 2
500 # 3
500 # 4
500 # 5
450 # 6
450 # 7
. . .
. . .
. . .
50 # 58
50 # 59
FILES
/usr/include/sys/fc.h
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fc_dptbl(4) fc_dptbl(4)
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 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.
Copyright 1994 Novell, Inc. Page 4