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fx_dptbl(4)                      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 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
                       priority level. The mapping between fixed-priority pri-
                       ority levels and global scheduling priorities is deter-
                       mined  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 prior-
                       ity  process can be changed by the user with the prioc-
                       ntl(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  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) 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 resolution
            to  be  used for interpreting the time quantum values. The resolu-
            tion is specified as:


            where res is a positive integer between 1 and 1,000,000,000 inclu-
            sive  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 quan-
            tum 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

   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  sup-

           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  dis-
       patch  table.  A  mistake  can result in panics, thus making the system

       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

       #   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

          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,
          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 *
          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 Guide

       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)