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rt_dptbl(4)                      File Formats                      rt_dptbl(4)



NAME
       rt_dptbl - real-time dispatcher parameter table

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 pol-
       icy, used to schedule processes within that class. Associated with each
       scheduling class is a set of priority queues on which ready to run pro-
       cesses are linked. These priority queues are mapped by the system  con-
       figuration  into a set of global scheduling priorities which are avail-
       able 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.

       The  real-time class maintains an in-core table, with an entry for each
       priority level, giving the properties of  that  level.  This  table  is
       called   the  real-time  dispatcher  parameter  table  (rt_dptbl).  The
       rt_dptbl consists of an array (config_rt_dptbl[]) of  parameter  struc-
       tures  (struct  rtdpent_t),  one for each of the n priority levels. The
       structure are accessed via a pointer, (rt_dptbl),  to  the  array.  The
       properties of a given priority level i are specified by the ith parame-
       ter structure in this array ( rt_dptbl[i] ).

       A parameter structure consists of the following members. These are also
       described in the /usr/include/sys/rt.h header file.

       rt_globpri      The  global  scheduling  priority  associated with this
                       priority level. The rt_globpri values cannot be changed
                       with dispadmin(1M).



       rt_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  real-time
                       process  can  be  changed by the user with the priocntl
                       command or the priocntl 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  real-time  portion  of
       the  scheduler  by  reconfiguring  the  rt_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.

   rt_dptbl Loadable Module
       The  rt_dptbl can be reconfigured with a loadable module which contains
       a new real time dispatch table. The module containing the dispatch  ta-
       ble  is separate from the RT loadable module which contains the rest of
       the real time software. This is the only method that  can  be  used  to
       change  the  number  of  real time priority levels or the set of global
       scheduling priorities used by the real time class. The relevant  proce-
       dure and source code is described in the EXAMPLES section.

   dispadmin Configuration File
       The rt_quantum values in the rt_dptbl can be examined and modified on a
       running system using the dispadmin(1M) command.  Invoking dispadmin for
       the  real-time  class  allows the administrator to retrieve the current
       rt_dptbl configuration from the kernel's in-core  table,  or  overwrite
       the in-core table with values from a configuration file. The configura-
       tion file used for input to dispadmin must conform to the specific for-
       mat described below.

       Blank lines are ignored and any part of a line to the right of a # sym-
       bol is treated as a comment. 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 exam-
       ple, RES=1000 specifies millisecond  resolution.)  Although  very  fine
       (nanosecond)  resolution may be specified, the time quantum lengths are
       rounded up to the next integral multiple of the system clock's  resolu-
       tion.

       The remaining lines in the file are used to specify the rt_quantum val-
       ues for each of the real-time priority levels. The first line specifies
       the  quantum for real-time level 0, the second line specifies the quan-
       tum for real-time level 1. There must be exactly one line for each con-
       figured  real-time priority level. Each rt_quantum entry must be either
       a positive integer specifying the desired time quantum (in the  resolu-
       tion given by res), or the value -2 indicating an infinite time quantum
       for that level.

EXAMPLES
       Example 1: A Sample dispadmin Configuration File

       The following excerpt from a dispadmin configuration  file  illustrates
       the  format. Note that for each line specifying a time quantum there is
       a comment indicating the corresponding priority level. These level num-
       bers  indicate  priority  within  the  real-time class, and the mapping
       between these real-time priorities and the corresponding global  sched-
       uling  priorities  is  determined by the configuration specified in the
       RT_DPTBL loadable module. The level numbers are strictly for the conve-
       nience  of the administrator reading the file and, as with any comment,
       they are ignored by dispadmin on  input.  dispadmin  assumes  that  the
       lines in the file are ordered by consecutive, increasing priority level
       (from 0 to the maximum configured real-time priority). The  level  num-
       bers  in  the comments should normally agree with this ordering; if for
       some reason they don't, however, dispadmin is unaffected.

       # Real-Time Dispatcher Configuration File
       RES=1000

       # TIME QUANTUM PRIORITY
       # (rt_quantum)LEVEL
       100#   0
       100#   1
       100#   2
       100#   3
       100#   4
       100#   5
       90 #   6
       90 #   7
       ..    .
       ..    .
       ..    .
       10#   58
       10#   59


       Example 2: Replacing The rt_dptbl Loadable Module

       In order to change the size of the real time dispatch table, the  load-
       able  module which contains the dispatch table information will have to
       be built. It is recommended that you save the  existing  module  before
       using the following procedure.

       1.  Place  the  dispatch  table  code  shown  below  in  a  file called
           rt_dptbl.c An example of an rt_dptbl.c file follows.


       2.  Compile the code using the given compilation and  link  lines  sup-
           plied.


           cc -c -0 -D_KERNEL rt_dptbl.c
           ld -r -o RT_DPTBL rt_dptbl.o


       3.  Copy   the   current   dispatch   table   in  /usr/kernel/sched  to
           RT_DPTBL.bak.


       4.  Replace the current RT_DPTBL in /usr/kernel/sched.


       5.  You will have to make changes in the /etc/system  file  to  reflect
           the  changes to the sizes of the tables. See system(4). The rt_max-
           pri variable may need changing. The syntax for setting this is:


           set RT:rt_maxpri=(class-specific value for maximum real-time priority)


       6.  Reboot the system to use the new dispatch table.


       Great care should be used in replacing the dispatch  table  using  this
       method. If you don't get it right, the system may not behave properly.

       The  following is an example of a rt_dptbl.c file used for building the
       new rt_dptbl.

       /*  BEGIN rt_dptbl.c  */
       #include <sys/proc.h>
       #include <sys/priocntl.h>
       #include <sys/class.h>
       #include <sys/disp.h>
       #include <sys/rt.h>
       #include <sys/rtpriocntl.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, "realtime dispatch table"
       };
       static struct modlinkage modlinkage = {
            MODREV_1, &modlmisc, 0
       };
       _init()
       {
            return (mod_install(&modlinkage));
       }
       _info (struct modinfo *modinfop)
       {
            return (mod_info(&modlinkage, modinfop));
       }
       rtdpent_t       config_rt_dptbl[] = {

       /*   prilevel Time quantum  */

       100,100,
       101,100,
       102,100,
       103,100,
       104,100,
       105,100,
       106,100,
       107,100,
       108,100,
       109,100,
       110,80,
       111,80,
       112,80,
       113,80,
       114,80,
       115,80,
       116,80,
       117,80,
       118,80,
       119,80,
       120,60,
       121,60,
       122,60,
       123,60,
       124,60,
       125,60,
       126,60,
       127,60,
       128,60,
       129,60,
       130,40,
       131,40,
       132,40,
       133,40,
       134,40,
       135,40,
       136,40,
       137,40,
       138,40,
       139,40,
       140,20,
       141,20,
       142,20,
       143,20,
       144,20,
       145,20,
       146,20,
       147,20,
       148,20,
       149,20,
       150,10,
       151,10,
       152,10,
       153,10,
       154,10,
       155,10,
       156,10,
       157,10,
       158,10,
       159,10,

       };
       /*
        * Return the address of config_rt_dptbl
        */ rtdpent_t *
           rt_getdptbl()
       {
                  return (config_rt_dptbl);
       }


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

       System Administration Guide: Basic Administration

        Programming Interfaces Guide



SunOS 5.10                        15 Oct 2002                      rt_dptbl(4)