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OpenSolaris 2009.06 - man page for rt_dptbl (opensolaris section 4)

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 alloca-
       tion 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 prior-
       ity) to n (highest priority--a configuration dependent value). The set of global  schedul-
       ing  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 parame-
       ter table (rt_dptbl). The rt_dptbl consists of an array (config_rt_dptbl[])  of	parameter
       structures  (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 parameter 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  pro-
		     cesses  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 table 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  procedure  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 ta-
       ble, 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 format described below.

       Blank  lines are ignored and any part of a line to the right of a # symbol 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  example,  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 resolution.

       The remaining lines in the file are used to specify the rt_quantum values for each of  the
       real-time priority levels. The first line specifies the quantum for real-time level 0, the
       second line specifies the quantum for real-time level 1. There must be  exactly	one  line
       for each configured real-time priority level. Each rt_quantum entry must be either a posi-
       tive integer specifying the desired time quantum (in the resolution 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 correspond-
       ing  priority level. These level numbers indicate priority within the real-time class, and
       the mapping between these real-time priorities and  the	corresponding  global  scheduling
       priorities  is  determined by the configuration specified in the RT_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 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 numbers 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  loadable  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  exam-
		  ple of an rt_dptbl.c file follows.

	   2.	  Compile the code using the given compilation and link lines supplied.

		    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_maxpri variable may need  chang-
		  ing. 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 5.11				   15 Oct 2002				      rt_dptbl(4)


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