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File Formats                                          fx_dptbl(4)

     fx_dptbl - fixed priority dispatcher parameter table


     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

           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).

           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

SunOS 5.9           Last change: 15 Oct 2002                    1

File Formats                                          fx_dptbl(4)

           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:


     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.

SunOS 5.9           Last change: 15 Oct 2002                    2

File Formats                                          fx_dptbl(4)

        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

     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.

     Example 1: Configuration File Excerpt

SunOS 5.9           Last change: 15 Oct 2002                    3

File Formats                                          fx_dptbl(4)

     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

     #   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

     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>

SunOS 5.9           Last change: 15 Oct 2002                    4

File Formats                                          fx_dptbl(4)

      * 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

        return (mod_install(&modlinkage));

        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,

SunOS 5.9           Last change: 15 Oct 2002                    5

File Formats                                          fx_dptbl(4)

        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;

SunOS 5.9           Last change: 15 Oct 2002                    6

File Formats                                          fx_dptbl(4)

      * Return the address of config_fx_dptbl
     fxdpent_t *
        return (config_fx_dptbl);

      * Return the address of fx_maxumdpri
      * the config_fx_dptbl table.
        return (config_fx_maxumdpri);

     priocntl(1), dispadmin(1M), priocntl(2), system(4)

     System Administration  Guide,  Volume  1,  System  Interface

     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.

SunOS 5.9           Last change: 15 Oct 2002                    7