fp_dptbl(4) fp_dptbl(4)
NAME
fp_dptbl - fixed priority 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 that
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).
The fixed priority class maintains an in-core table, with an
entry for each priority level, giving the properties of that
level. This table is called the fixed priority dispatcher
parameter table (fp_dptbl). The fp_dptbl consists of an array
of parameter structures (struct fp_dpent), one for each of the
n priority levels. The properties of a given priority level i
are specified by the ith parameter structure in this array
(fp_dptbli).
A parameter structure consists of the following members.
These are also described in the /usr/include/sys/fp.h header
file.
fp_globpri
The global scheduling priority associated with this
priority level. The mapping between fixed priority
levels and global scheduling priorities is determined
at boot time by the system configuration. The
fp_globpri values cannot be changed with
dispadmin(1M).
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fp_dptbl(4) fp_dptbl(4)
fp_quantum
The length of the time quantum allocated to processes
at this level in ticks (HZ). The time quantum value
is only a default or starting value for processes at a
particular level as the time quantum of a fixed
priority process can be changed by the user with the
priocntl command or the priocntl system call.
An administrator can affect the behavior of the fixed priority
portion of the scheduler by reconfiguring the fp_dptbl. There
are two methods available for doing this.
DISPADMIN CONFIGURATION FILE
The fp_quantum values in the fp_dptbl can be examined and
modified on a running system using the dispadmin(1M) command.
Invoking dispadmin for the fixed priority class allows the
administrator to retrieve the current fp_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 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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fp_dptbl(4) fp_dptbl(4)
The remaining lines in the file are used to specify the
fp_quantum values for each of the fixed priority levels. The
first line specifies the quantum for fixed priority level 0,
the second line specifies the quantum for fixed priority level
1, and so on. There must be exactly one line for each
configured fixed priority level. Each fp_quantum entry must
be either a positive integer specifying the desired time
quantum (in the resolution given by res), or the symbol
RT_TQINF indicating an infinite time quantum for that level.
EXAMPLE
The following excerpt from a dispadmin configuration file
illustrates the format. Note that for each line specifying a
time quantum there is a comment indicating the corresponding
priority level. These level numbers indicate priority within
the fixed priority class, and the mapping between these fixed
priorities and the corresponding global scheduling priorities
is determined by the configuration specified in the fp 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 on input. dispadmin assumes
that the lines in the file are ordered by consecutive,
increasing priority level (from 0 to the maximum configured
fixed priority). The level numbers in the comments should
normally agree with this ordering; if for some reason they
don't, however, dispadmin is unaffected.
# Real-Time Dispatcher Configuration File
RES=1000
# TIME QUANTUM PRIORITY
# (fp_quantum) LEVEL
100 # 0
100 # 1
100 # 2
100 # 3
100 # 4
100 # 5
90 # 6
90 # 7
. . .
. . .
. . .
10 # 58
10 # 59
Copyright 1994 Novell, Inc. Page 3
fp_dptbl(4) fp_dptbl(4)
FILES
/usr/include/sys/fp.h
REFERENCES
dispadmin(1M), priocntl(1), priocntl(2)
Copyright 1994 Novell, Inc. Page 4