fx_dptbl(4) File Formats fx_dptbl(4)NAMEfx_dptbl - fixed priority dispatcher parameter table
SYNOPSISfx_dptblDESCRIPTION
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-depen‐
dent 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 parame‐
ter structures (struct fxdpent_t), one for each of the n priority lev‐
els 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 struc‐
ture 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 pri‐
ority 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 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 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) command. Invoking dispadmin for
the fixed-priority class allows the administrator to retrieve the cur‐
rent fx_dptbl configuration from the kernel's in-core table or over‐
write the in-core table with values from a configuration file. The con‐
figuration file used for input to dispadmin must conform to the spe‐
cific 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 res‐
olution 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 res‐
olution). 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-pri‐
ority 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 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 dis‐
patch 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 param‐
eters, 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 correspond‐
ing 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 com‐
mand assumes that the lines in the file are ordered by consecutive,
increasing priority level (from 0 to the maximum configured fixed-pri‐
ority 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);
}
SEE ALSOpriocntl(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 maximum priority in the FX
class. Unusual fx_dptbl configurations may have significant negative
impact on the performance of the nfsd and lockd daemons.
SunOS 5.10 15 Oct 2002 fx_dptbl(4)
