/usr/src/man/man4/fx_dptbl.4

'\" te
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.TH FX_DPTBL 4 "Oct 15, 2002"
.SH NAME
fx_dptbl \- fixed priority dispatcher parameter table
.SH SYNOPSIS
.LP
.nf
\fBfx_dptbl\fR
.fi

.SH DESCRIPTION
.sp
.LP
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 \fIn\fR (highest priority\(ema
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.
.sp
.LP
Processes in the fixed priority class are scheduled according to the parameters
in a fixed-priority dispatcher parameter table (\fBfx_dptbl\fR). The
\fBfx_dptbl\fR table consists of an array (\fBconfig_fx_dptbl[]\fR) of
parameter structures (\fBstruct fxdpent_t\fR), one for each of the \fIn\fR
priority levels used by fixed priority processes in user mode. The structures
are accessed by way of a pointer, (\fBfx_dptbl\fR), to the array. The
properties of a given priority level \fIi\fR are specified by the \fIi\fRth
parameter structure in this array (\fBfx_dptbl[\fIi\fR]\fR).
.sp
.LP
A parameter structure consists of the following members. These are also
described in the \fB/usr/include/sys/fx.h\fR header.
.sp
.ne 2
.na
\fB\fBfx_globpri\fR\fR
.ad
.RS 14n
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. \fBfx_globpri\fR can not
be changed with \fBdispadmin\fR(1M).
.RE

.sp
.ne 2
.na
\fB\fBfx_quantum\fR\fR
.ad
.RS 14n
The length of the time quantum allocated to processes at this level in ticks
(\fBhz\fR). 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 \fBpriocntl\fR(1) command or the
\fBpriocntl\fR(2) system call.
.sp
In the high resolution clock mode (\fBhires_tick\fR set to \fB1\fR), the value
of \fBhz\fR is set to \fB1000\fR. Increase quantums to maintain the same
absolute time quantums.
.sp
An administrator can affect the behavior of the fixed priority portion of the
scheduler by reconfiguring the \fBfx_dptbl\fR. There are two methods available
for doing this: reconfigure with a loadable module at boot-time or by using
\fBdispadmin\fR(1M) at run-time.
.RE

.SS "fx_dptbl Loadable Module"
.sp
.LP
The \fBfx_dptbl\fR 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 \fBFX\fR 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.
.SS "dispadmin Configuration File"
.sp
.LP
The \fBfx_quantum\fR values in the \fBfx_dptbl\fR can be examined and modified
on a running system using the \fBdispadmin\fR(1M) command. Invoking
\fBdispadmin\fR for the fixed-priority class allows the administrator to
retrieve the current \fBfx_dptbl\fR 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 \fBdispadmin\fR must conform to the
specific format described as follows:
.RS +4
.TP
.ie t \(bu
.el o
Blank lines are ignored and any part of a line to the right of a # symbol is
treated as a comment.
.RE
.RS +4
.TP
.ie t \(bu
.el 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:
.sp
.in +2
.nf
RES=\fIres\fR
.fi
.in -2
.sp

where \fIres\fR is a positive integer between 1 and 1,000,000,000 inclusive and
the resolution used is the reciprocal of \fIres\fR in seconds (for example,
\fBRES=1000\fR 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.
.RE
.RS +4
.TP
.ie t \(bu
.el o
The remaining lines in the file are used to specify the \fBfx_quantum\fR 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 \fBfx_quantum\fR entry must be a
positive integer specifying the desired time quantum in the resolution given by
\fIres\fR.
.RE
.sp
.LP
See Examples for an example of an excerpt of a \fBdispadmin\fR configuration
file.
.SS "Replacing the fx_dptbl Loadable Module"
.sp
.LP
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.
.RS +4
.TP
1.
Place the dispatch table code shown below in a file called \fBfx_dptbl.c\fR.
See EXAMPLES, below, for an example of this file.
.RE
.RS +4
.TP
2.
Compile the code using the given compilation and link lines supplied:
.sp
.in +2
.nf
cc -c -0 -D_KERNEL fx_dptbl.c
ld -r -o FX_DPTBL fx_dptbl.o
.fi
.in -2
.sp

.RE
.RS +4
.TP
3.
Copy the current dispatch table in \fB/usr/kernel/sched\fR to
\fBFX_DPTBL.bak\fR.
.RE
.RS +4
.TP
4.
Replace the current \fBFX_DPTBL\fR in \fB/usr/kernel/sched\fR.
.RE
.RS +4
.TP
5.
Make changes in the \fB/etc/system\fR file to reflect the changes to the
sizes of the tables. See \fBsystem\fR(4). The variables affected is
\fBfx_maxupri\fR. The syntax for setting this is as follows:
.sp
.in +2
.nf
set  FX:fx_maxupri=(\fIvalue for max fixed-priority user priority\fR)
.fi
.in -2
.sp

.RE
.RS +4
.TP
6.
Reboot the system to use the new dispatch table.
.RE
.sp
.LP
Exercise great care in using the preceding method to replace the dispatch
table. A mistake can result in panics, thus making the system unusable.
.SH EXAMPLES
.LP
\fBExample 1 \fRConfiguration File Excerpt
.sp
.LP
The following excerpt from a \fBdispadmin\fR 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 \fBFX_DPTBL\fR 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 \fBdispadmin\fR.
The \fBdispadmin\fR 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, \fBdispadmin\fR is unaffected.

.sp
.in +2
.nf
# 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
.fi
.in -2
.sp

.LP
\fBExample 2 \fR\fBfx_dptbl.c\fR File Used for Building the New \fBfx_dptbl\fR
.sp
.LP
The following is an example of a \fBfx_dptbl.c\fR file used for building the
new \fBfx_dptbl\fR.

.sp
.in +2
.nf
/* 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);
}
.fi
.in -2
.sp

.SH SEE ALSO
.sp
.LP
\fBpriocntl\fR(1), \fBdispadmin\fR(1M), \fBpriocntl\fR(2), \fBsystem\fR(4)
.sp
.LP
\fISystem Administration Guide, Volume 1, System Interface Guide\fR
.SH NOTES
.sp
.LP
In order to improve performance under heavy system load, both the \fBnfsd\fR
daemon and the \fBlockd\fR daemon utilize the maximum priority in the \fBFX\fR
class. Unusual \fBfx_dptbl\fR configurations may have significant negative
impact on the performance of the \fBnfsd\fR and \fBlockd\fR daemons.