fx_dptbl(4)
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 pro-
cess with the highest global scheduling priority in the sys-
tem. 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, depend-
ing on the configuration.
Processes in the fixed priority class are scheduled accord-
ing to the parameters in a fixed-priority dispatcher parame-
ter 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(1M).
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 high resolution clock mode (hires_tick set to
1), the value of hz is set to 1000. Increase quantums
to maintain the same absolute time quantums.
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(1M) 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 load-
able 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(1M) com-
mand. 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(4). 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 indicat-
ing the corresponding priority level. These level numbers
indicate priority within the fixed priority class; the map-
ping 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, dispad-
min 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);
}
SEE ALSO
priocntl(1), dispadmin(1M), priocntl(2), system(4)
System Administration Guide, Volume 1, System Interface
Guide
NOTES
In order to improve performance under heavy system load,
both the nfsd daemon and the lockd daemon utilize the max-
imum priority in the FX class. Unusual fx_dptbl configura-
tions may have significant negative impact on the perfor-
mance of the nfsd and lockd daemons.
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