Tribblix: manual page: fx

FX_DPTBL(5) File Formats and Configurations FX_DPTBL(5)

NAME

fx_dptbl - fixed priority dispatcher parameter table

SYNOPSIS

fx_dptbl

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 priority class are scheduled according to the
parameters in a fixed-priority dispatcher parameter table (fx_dptbl).
The fx_dptbl table consists of an array (config_fx_dptbl[]) of
parameter structures (struct fxdpent_t), one for each of the n
priority levels used by fixed priority processes in user mode. The
structures are accessed by way of a pointer, (fx_dptbl), to the
array. The properties of a given priority level i are specified by
the ith parameter structure in this array (fx_dptbl[i]).

A parameter structure consists of the following members. These are
also described in the /usr/include/sys/fx.h header.

fx_globpri
The global scheduling priority associated with this
priority level. The mapping between fixed-priority
priority levels and global scheduling priorities is
determined at boot time by the system configuration.
fx_globpri can not be changed with dispadmin(8).

fx_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(1) command or the priocntl(2) system call.

In the default high resolution clock mode (hires_tick
set to 1), the value of hz is set to 1000. If this
value is overridden to 0 then hz will instead be 100;
the number of ticks per quantum must then be decreased
to maintain the same length of quantum in absolute
time.

An administrator can affect the behavior of the fixed
priority portion of the scheduler by reconfiguring the
fx_dptbl. There are two methods available for doing
this: reconfigure with a loadable module at boot-time
or by using dispadmin(8) at run-time.

fx_dptbl Loadable Module
The fx_dptbl can be reconfigured with a loadable module that contains
a new fixed priority dispatch table. The module containing the
dispatch table is separate from the FX loadable module, which
contains the rest of the fixed priority software. This is the only
method that can be used to change the number of fixed priority
priority levels or the set of global scheduling priorities used by
the fixed priority class. The relevant procedure and source code is
described in Replacing the fx_dptbl Loadable Module below.

dispadmin Configuration File
The fx_quantum values in the fx_dptbl can be examined and modified on
a running system using the dispadmin(8) command. Invoking dispadmin
for the fixed-priority class allows the administrator to retrieve the
current fx_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 as follows:

o Blank lines are ignored and any part of a line to the
right of a # symbol is treated as a comment.

o 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 you can
specify very fine (nanosecond) resolution, the time
quantum lengths are rounded up to the next integral
multiple of the system clock's resolution.

o The remaining lines in the file are used to specify the
fx_quantum values for each of the fixed-priority 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 forth. There must be
exactly one line for each configured fixed priority
priority level. Each fx_quantum entry must be a positive
integer specifying the desired time quantum in the
resolution given by res.

See Examples for an example of an excerpt of a dispadmin
configuration file.

Replacing the fx_dptbl Loadable Module
To change the size of the fixed priority dispatch table, you must
build the loadable module that contains the dispatch table
information. Save the existing module before using the following
procedure.

1. Place the dispatch table code shown below in a file called
fx_dptbl.c. See EXAMPLES, below, for an example of this
file.

2. Compile the code using the given compilation and link
lines supplied:

cc -c -0 -D_KERNEL fx_dptbl.c
ld -r -o FX_DPTBL fx_dptbl.o

3. Copy the current dispatch table in /usr/kernel/sched to
FX_DPTBL.bak.

4. Replace the current FX_DPTBL in /usr/kernel/sched.

5. Make changes in the /etc/system file to reflect the
changes to the sizes of the tables. See system(5). The
variables affected is fx_maxupri. The syntax for setting
this is as follows:

set FX:fx_maxupri=(value for max fixed-priority user priority)

6. Reboot the system to use the new dispatch table.

Exercise great care in using the preceding method to replace the
dispatch table. A mistake can result in panics, thus making the
system unusable.

EXAMPLES

Example 1: Configuration File Excerpt

The following excerpt from a dispadmin configuration file illustrates
the correct 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
priority class; the mapping between these fixed-priority priorities
and the corresponding global scheduling priorities is determined by
the configuration specified in the FX_DPTBL loadable module. The
level numbers are strictly for the convenience of the administrator
reading the file and, as with any comment, they are ignored by
dispadmin. The dispadmin command assumes that the lines in the file
are ordered by consecutive, increasing priority level (from 0 to the
maximum configured fixed-priority priority). For the sake of someone
reading the file, the level numbers in the comments should agree with
this ordering. If for some reason they do not, dispadmin is
unaffected.

# Fixed Priority Dispatcher Configuration File RES=1000

RES=1000
# TIME QUANTUM PRIORITY
# (fx_quantum) LEVEL
200 # 0
200 # 1
200 # 2
200 # 3
200 # 4
200 # 5
200 # 6
200 # 7
. . .
. . .
. . .
20 # 58
20 # 59
20 # 60

Example 2 fx_dptbl.c File Used for Building the New fx_dptbl

The following is an example of a fx_dptbl.c file used for building
the new fx_dptbl.

/* BEGIN fx_dptbl.c */

#include <sys/proc.h>
#include <sys/priocntl.h>
#include <sys/class.h>
#include <sys/disp.h>
#include <sys/fx.h>
#include <sys/fxpriocntl.h>

/*
* This is the loadable module wrapper.
*/

#include <sys/modctl.h>

extern struct mod_ops mod_miscops;

/*
* Module linkage information for the kernel.
*/

static struct modlmisc modlmisc = {
&mod_miscops, "Fixed priority dispatch table"
};

static struct modlinkage modlinkage = {
MODREV_1, &modlmisc, 0
};

_init()
{
return (mod_install(&modlinkage));
}

_info(modinfop)
struct modinfo *modinfop;
{
return (mod_info(&modlinkage, modinfop));
}

#define FXGPUP0 0 /* Global priority for FX user priority 0 */
fxdpent_t config_fx_dptbl[] = {

/* glbpri qntm */

FXGPUP0+0, 20,
FXGPUP0+1, 20,
FXGPUP0+2, 20,
FXGPUP0+3, 20,
FXGPUP0+4, 20,
FXGPUP0+5, 20,
FXGPUP0+6, 20,
FXGPUP0+7, 20,
FXGPUP0+8, 20,
FXGPUP0+9, 20,
FXGPUP0+10, 16,
FXGPUP0+11, 16,
FXGPUP0+12, 16,
FXGPUP0+13, 16,
FXGPUP0+14, 16,
FXGPUP0+15, 16,
FXGPUP0+16, 16,
FXGPUP0+17, 16,
FXGPUP0+18, 16,
FXGPUP0+19, 16,
FXGPUP0+20, 12,
FXGPUP0+21, 12,
FXGPUP0+22, 12,
FXGPUP0+23, 12,
FXGPUP0+24, 12,
FXGPUP0+25, 12,
FXGPUP0+26, 12,
FXGPUP0+27, 12,
FXGPUP0+28, 12,
FXGPUP0+29, 12,
FXGPUP0+30, 8,
FXGPUP0+31, 8,
FXGPUP0+32, 8,
FXGPUP0+33, 8,
FXGPUP0+34, 8,
FXGPUP0+35, 8,
FXGPUP0+36, 8,
FXGPUP0+37, 8,
FXGPUP0+38, 8,
FXGPUP0+39, 8,
FXGPUP0+40, 4,
FXGPUP0+41, 4,
FXGPUP0+42, 4,
FXGPUP0+43, 4,
FXGPUP0+44, 4,
FXGPUP0+45, 4,
FXGPUP0+46, 4,
FXGPUP0+47, 4,
FXGPUP0+48, 4,
FXGPUP0+49, 4,
FXGPUP0+50, 4,
FXGPUP0+51, 4,
FXGPUP0+52, 4,
FXGPUP0+53, 4,
FXGPUP0+54, 4,
FXGPUP0+55, 4,
FXGPUP0+56, 4,
FXGPUP0+57, 4,
FXGPUP0+58, 4,
FXGPUP0+59, 2,
FXGPUP0+60 2,
};

pri_t config_fx_maxumdpri =
sizeof (config_fx_dptbl) / sizeof (fxdpent_t) - 1;

/*
* Return the address of config_fx_dptbl
*/
fxdpent_t *
fx_getdptbl()
{
return (config_fx_dptbl);
}

/*
* Return the address of fx_maxumdpri
*/
pri_t
fx_getmaxumdpri()
{
/*
* the config_fx_dptbl table.
*/
return (config_fx_maxumdpri);
}

NOTES