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fx_dptbl
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 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 header. fx_globpri
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(8).
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 priority process can be changed by the user with the priocntl(1) command or the priocntl(2) system call. In the default high resolution clock mode (hires_tick set to 1), the value of hz is set to 1000. If this value is overridden to 0 then hz will instead be 100; the number of ticks per quantum must then be decreased to maintain the same length of quantum in absolute time. 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(8) at run-time.
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 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.
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.
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
5. Make changes in the /etc/system file to reflect the changes to the sizes of the tables. See system(5). 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.
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 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 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, dispadmin is unaffected.
# 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
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 }; _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); }
System Administration Guide, Volume 1, System Interface Guide