The priocntl() function provides for control over the scheduling of an active light weight process (LWP).

LWPs fall into distinct classes with a separate scheduling policy applied to each class. The classes currently supported are the realtime class, the time-sharing class, the fair-share class, and the fixed-priority class. The characteristics of these classes are described under the corresponding headings below.

The class attribute of an LWP is inherited across the fork(2) and _lwp_create(2) functions and the exec family of functions (see exec(2)). The priocntl() function can be used to dynamically change the class and other scheduling parameters associated with a running LWP or set of LWPs given the appropriate permissions as explained below.

In the default configuration, a runnable realtime LWP runs before any other LWP. Therefore, inappropriate use of realtime LWP can have a dramatic negative impact on system performance.

The priocntl() function provides an interface for specifying a process, set of processes, or an LWP to which the function applies. The priocntlset(2) function provides the same functions as priocntl(), but allows a more general interface for specifying the set of LWPs to which the function is to apply.

For priocntl(), the idtype and id arguments are used together to specify the set of LWPs. The interpretation of id depends on the value of idtype. The possible values for idtype and corresponding interpretations of id are as follows:

P_ALL

The priocntl() function applies to all existing LWPs. The value of id is ignored. The permission restrictions described below still apply.

P_CID

The id argument is a class ID (returned by the priocntl() PC_GETCID command as explained below). The priocntl() function applies to all LWPs in the specified class.

P_GID

The id argument is a group ID. The priocntl() function applies to all LWPs with this effective group ID.

P_LWPID

The id argument is an LWP ID. The priocntl function applies to the LWP with the specified ID within the calling process.

P_PGID

The id argument is a process group ID. The priocntl() function applies to all LWPs currently associated with processes in the specified process group.

P_PID

The id argument is a process ID specifying a single process. The priocntl() function applies to all LWPs currently associated with the specified process.

P_PPID

The id argument is a parent process ID. The priocntl() function applies to all LWPs currently associated with processes with the specified parent process ID.

P_PROJID

The id argument is a project ID. The priocntl() function applies to all LWPs with this project ID.

P_SID

The id argument is a session ID. The priocntl() function applies to all LWPs currently associated with processes in the specified session.

P_TASKID

The id argument is a task ID. The priocntl() function applies to all LWPs currently associated with processes in the specified task.

P_UID

The id argument is a user ID. The priocntl() function applies to all LWPs with this effective user ID.

An id value of P_MYID can be used in conjunction with the idtype value to specify the LWP ID, parent process ID, process group ID, session ID, task ID, class ID, user ID, group ID, or project ID of the calling LWP.

To change the scheduling parameters of an LWP (using the PC_SETPARMS or PC_SETXPARMS command as explained below) , the real or effective user ID of the LWP calling priocntl() must match the real or effective user ID of the receiving LWP or the effective user ID of the calling LWP must be superuser. These are the minimum permission requirements enforced for all classes. An individual class might impose additional permissions requirements when setting LWPs to that class and/or when setting class-specific scheduling parameters.

A special SYS scheduling class exists for the purpose of scheduling the execution of certain special system processes (such as the swapper process). It is not possible to change the class of any LWP to SYS. In addition, any processes in the SYS class that are included in a specified set of processes are disregarded by priocntl(). For example, an idtype of P_UID and an id value of 0 would specify all processes with a user ID of 0 except processes in the SYS class and (if changing the parameters using PC_SETPARMS or PC_SETXPARMS) the init(1M) process.

The init process is a special case. For a priocntl() call to change the class or other scheduling parameters of the init process (process ID 1), it must be the only process specified by idtype and id. The init process can be assigned to any class configured on the system, but the time-sharing class is almost always the appropriate choice. (Other choices might be highly undesirable. See the System Administration Guide: Basic Administration for more information.)

The data type and value of arg are specific to the type of command specified by cmd.

A pcinfo_t structure with the following members, defined in <sys/priocntl.h>, is used by the PC_GETCID and PC_GETCLINFO commands.

id_t pc_cid; /* Class id */ char pc_clname[PC_CLNMSZ]; /* Class name */ int pc_clinfo[PC_CLINFOSZ]; /* Class information */

The pc_cid member is a class ID returned by the priocntl() PC_GETCID command. The pc_clname member is a buffer of size PC_CLNMSZ, defined in <sys/priocntl.h>, used to hold the class name: RT for realtime, TS for time-sharing, or FX for fixed-priority.

The pc_clinfo member is a buffer of size PC_CLINFOSZ, defined in <sys/priocntl.h>, used to return data describing the attributes of a specific class. The format of this data is class-specific and is described under the appropriate heading (REALTIME CLASS, TIME-SHARING CLASS, or FIXED-PRIORITY CLASS) below.

A pcparms_t structure with the following members, defined in <sys/priocntl.h>, is used by the PC_SETPARMS and PC_GETPARMS commands.

id_t pc_cid; /* LWP class */ int pc_clparms[PC_CLPARMSZ]; /* Class-specific params */

The pc_cid member is a class ID returned by the priocntl() PC_GETCID command. The special class ID PC_CLNULL can also be assigned to pc_cid when using the PC_GETPARMS command as explained below.

The pc_clparms buffer holds class-specific scheduling parameters. The format of this parameter data for a particular class is described under the appropriate heading below. PC_CLPARMSZ is the length of the pc_clparms buffer and is defined in <sys/priocntl.h>.

The PC_SETXPARMS and PC_GETXPARMS commands exploit the varargs declaration of priocntl(). The argument following the command code is a class name: RT for realtime, TS for time-sharing, or FX for fixed-priority. The parameters after the class name build a chain of (key, value) pairs, where the key determines the meaning of the value within the pair. When using PC_GETXPARMS, the value associated with the key is always a pointer to a scheduling parameter. In contrast, when using PC_SETXPARMS the scheduling parameter is given as a direct value. A key value of 0 terminates the sequence and all further keys or values are ignored.

The PC_SETXPARMS and PC_GETXPARMS commands are more flexible thanPC_SETPARMS and PC_GETPARMS and should replace PC_SETPARMS and PC_GETPARMS on a long-term basis.

Available priocntl() commands are:

PC_ADMIN

This command provides functionality needed for the implementation of the dispadmin(1M) utility. It is not intended for general use by other applications.

PC_DONICE

Set or get nice value of the specified LWP(s) associated with the specified process(es). When this command is used with the idtype of P_LWPID, it sets the nice value of the LWP. The arg argument points to a structure of type pcnice_t. The pc_val member specifies the nice value and the pc_op specifies the type of the operation.

When pc_op is set to PC_GETNICE, priocntl() sets the pc_val to the highest priority (lowest numerical value) pertaining to any of the specified LWPs.

When pc_op is set to PC_SETNICE, priocntl() sets the nice value of all LWPs in the specified set to the value specified in pc_val member of pcnice_t structure.

The priocntl() function returns -1 with errno set to EPERM if the calling LWP doesn't have appropriate permissions to set or get nice values for one or more of the target LWPs. If priocntl() encounters an error other than permissions, it does not continue through the set of target LWPs but returns the error immediately.

PC_GETCID

Get class ID and class attributes for a specific class given the class name. The idtype and id arguments are ignored. If arg is non-null, it points to a structure of type pcinfo_t. The pc_clname buffer contains the name of the class whose attributes you are getting.

On success, the class ID is returned in pc_cid, the class attributes are returned in the pc_clinfo buffer, and the priocntl() call returns the total number of classes configured in the system (including the sys class). If the class specified by pc_clname is invalid or is not currently configured, the priocntl() call returns -1 with errno set to EINVAL. The format of the attribute data returned for a given class is defined in the <sys/rtpriocntl.h>, <sys/tspriocntl.h>, or <sys/fxpriocntl.h> header and described under the appropriate heading below.

If arg is a null pointer, no attribute data is returned but the priocntl() call still returns the number of configured classes.

PC_GETCLINFO

Get class name and class attributes for a specific class given class ID. The idtype and id arguments are ignored. If arg is non-null, it points to a structure of type pcinfo_t. The pc_cid member is the class ID of the class whose attributes you are getting.

On success, the class name is returned in the pc_clname buffer, the class attributes are returned in the pc_clinfo buffer, and the priocntl() call returns the total number of classes configured in the system (including the sys class). The format of the attribute data returned for a given class is defined in the <sys/rtpriocntl.h>, <sys/tspriocntl.h>, or <sys/fxpriocntl.h> header and described under the appropriate heading below.

If arg is a null pointer, no attribute data is returned but the priocntl() call still returns the number of configured classes.

PC_GETPARMS

Get the class and/or class-specific scheduling parameters of an LWP. The arg member points to a structure of type pcparms_t.

If pc_cid specifies a configured class and a single LWP belonging to that class is specified by the idtype and id values or the procset structure, then the scheduling parameters of that LWP are returned in the pc_clparms buffer. If the LWP specified does not exist or does not belong to the specified class, the priocntl() call returns -1 with errno set to ESRCH.

If pc_cid specifies a configured class and a set of LWPs is specified, the scheduling parameters of one of the specified LWP belonging to the specified class are returned in the pc_clparms buffer and the priocntl() call returns the process ID of the selected LWP. The criteria for selecting an LWP to return in this case is class-dependent. If none of the specified LWPs exist or none of them belong to the specified class, the priocntl() call returns -1 with errno set to ESRCH.

If pc_cid is PC_CLNULL and a single LWP is specified, the class of the specified LWP is returned in pc_cid and its scheduling parameters are returned in the pc_clparms buffer.

PC_GETXPARMS

Get the class or class-specific scheduling parameters of an LWP. The class name (first argument after PC_GETXPARMS) specifies the class and the (key, value) pair sequence contains a pointer to the class-specific parameters. The keys and the types of the class-specific parameter data are described below and can also be found in the class-specific headers <sys/rtpriocntl.h>, <sys/tspriocntl.h>, and <sys/fxpriocntl.h>. If the specified class is a configured class and a single LWP belonging to that class is specified by the idtype and id values or the procset structure, then the scheduling parameters of that LWP are returned in the given (key, value) pair buffers. If the LWP specified does not exist or does not belong to the specified class, priocntl() returns -1 and errno is set to ESRCH.

If the class name specifies a configured class and a set of LWPs is given, the scheduling parameters of one of the specified LWPs belonging to the specified class are returned and the priocntl() call returns the process ID of the selected LWP. The criteria for selecting an LWP to return in this case is class-dependent. If none of the specified LWPs exist or none of them belong to the specified class, priocntl() returns -1 and errno is set to ESRCH.

If the class name is a null pointer, a single process or LWP is specified, and a (key, value) pair for a class name request is given, priocntl() fills the buffer pointed to by value with the class name of the specified process or LWP. The key for the class name request is PC_KY_CLNAME and the class name buffer should be declared as:

char pc_clname[PC_CLNMSZ]; /* Class name */

PC_SETPARMS

Set the class and class-specific scheduling parameters of the specified LWP(s) associated with the specified process(es). When this command is used with the idtype of P_LWPID, it will set the class and class-specific scheduling parameters of the LWP. The arg argument points to a structure of type pcparms_t. The pc_cid member specifies the class you are setting and the pc_clparms buffer contains the class-specific parameters you are setting. The format of the class-specific parameter data is defined in the <sys/rtpriocntl.h>, <sys/tspriocntl.h>, or <sys/fxpriocntl.h> header and described under the appropriate class heading below.

When setting parameters for a set of LWPs, priocntl() acts on the LWPs in the set in an implementation-specific order. If priocntl() encounters an error for one or more of the target processes, it might or might not continue through the set of LWPs, depending on the nature of the error. If the error is related to permissions (EPERM), priocntl() continues through the LWP set, resetting the parameters for all target LWPs for which the calling LWP has appropriate permissions. The priocntl() function then returns -1 with errno set to EPERM to indicate that the operation failed for one or more of the target LWPs. If priocntl() encounters an error other than permissions, it does not continue through the set of target LWPs but returns the error immediately.

PC_SETXPARMS

Set the class and class-specific scheduling parameters of the specified LWP(s) associated with the specified process(es). When this command is used with P_LWPID as idtype, it will set the class and class-specific scheduling parameters of the LWP. The class name (first argument after PC_SETXPARMS) specifies the class to be changed and the following (key, value) pair sequence contains the class-specific parameters to be changed. Only those (key,value) pairs whose scheduling behavior is to change must be specified. The keys and the types of the class-specific parameter data are described below and can also be found in the class-specific header files <sys/rtpriocntl.h>, <sys/tspriocntl.h>, and <sys/fxpriocntl.h>.

When setting parameters for a set of LWPs, priocntl() acts on the LWPs in the set in an implementation-specific order. If priocntl() encounters an error for one or more of the target processes, it might or might not continue through the set of LWPs, depending on the nature of the error. If the error is related to permissions (EPERM), priocntl() continues to reset the parameters for all target LWPs where the calling LWP has appropriate permissions. The priocntl() function returns -1 and errno is set to EPERM when the operation failed for one or more of the target LWPs. All errors other than EPERM result in an immediate termination of priocntl().

The realtime class provides a fixed priority preemptive scheduling policy for those LWPS requiring fast and deterministic response and absolute user/application control of scheduling priorities. If the realtime class is configured in the system, it should have exclusive control of the highest range of scheduling priorities on the system. This ensures that a runnable realtime LWP is given CPU service before any LWP belonging to any other class.

The realtime class has a range of realtime priority (rt_pri) values that can be assigned to an LWP within the class. Realtime priorities range from 0 to x, where the value of x is configurable and can be determined for a specific installation by using the priocntl() PC_GETCID or PC_GETCLINFO command.

The realtime scheduling policy is a fixed priority policy. The scheduling priority of a realtime LWP is never changed except as the result of an explicit request by the user/application to change the rt_pri value of the LWP.

For an LWP in the realtime class, the rt_pri value is, for all practical purposes, equivalent to the scheduling priority of the LWP. The rt_pri value completely determines the scheduling priority of a realtime LWP relative to other LWPs within its class. Numerically higher rt_pri values represent higher priorities. Since the realtime class controls the highest range of scheduling priorities in the system, it is guaranteed that the runnable realtime LWP with the highest rt_pri value is always selected to run before any other LWPs in the system.

In addition to providing control over priority, priocntl() provides for control over the length of the time quantum allotted to the LWP in the realtime class. The time quantum value specifies the maximum amount of time an LWP can run assuming that it does not complete or enter a resource or event wait state (sleep). If another LWP becomes runnable at a higher priority, the currently running LWP might be preempted before receiving its full time quantum.

The realtime quantum signal can be used for the notification of runaway realtime processes about the consumption of their time quantum. Those processes, which are monitored by the realtime time quantum signal, receive the configured signal in the event of time quantum expiration. The default value (0) of the time quantum signal will denote no signal delivery and a positive value will denote the delivery of the signal specified by the value. The realtime quantum signal can be set with the priocntl() PC_SETXPARMS command and displayed with the priocntl() PC_GETXPARMS command as explained below.

The system's process scheduler keeps the runnable realtime LWPs on a set of scheduling queues. There is a separate queue for each configured realtime priority and all realtime LWPs with a given rt_pri value are kept together on the appropriate queue. The LWPs on a given queue are ordered in FIFO order (that is, the LWP at the front of the queue has been waiting longest for service and receives the CPU first). Realtime LWPs that wake up after sleeping, LWPs that change to the realtime class from some other class, LWPs that have used their full time quantum, and runnable LWPs whose priority is reset by priocntl() are all placed at the back of the appropriate queue for their priority. An LWP that is preempted by a higher priority LWP remains at the front of the queue (with whatever time is remaining in its time quantum) and runs before any other LWP at this priority. Following a fork(2) or _lwp_create(2) function call by a realtime LWP, the parent LWP continues to run while the child LWP (which inherits its parent's rt_pri value) is placed at the back of the queue.

A rtinfo_t structure with the following members, defined in <sys/rtpriocntl.h>, defines the format used for the attribute data for the realtime class.

short rt_maxpri; /* Maximum realtime priority */

The priocntl() PC_GETCID and PC_GETCLINFO commands return realtime class attributes in the pc_clinfo buffer in this format.

The rt_maxpri member specifies the configured maximum rt_pri value for the realtime class. If rt_maxpri is x, the valid realtime priorities range from 0 to x.

A rtparms_t structure with the following members, defined in <sys/rtpriocntl.h>, defines the format used to specify the realtime class-specific scheduling parameters of an LWP.

short rt_pri; /* Real-Time priority */ uint_t rt_tqsecs; /* Seconds in time quantum */ int rt_tqnsecs; /* Additional nanoseconds in quantum */

When using the priocntl() PC_SETPARMS or PC_GETPARMS commands, if pc_cid specifies the realtime class, the data in the pc_clparms buffer are in this format.

These commands can be used to set the realtime priority to the specified value or get the current rt_pri value. Setting the rt_pri value of an LWP that is currently running or runnable (not sleeping) causes the LWP to be placed at the back of the scheduling queue for the specified priority. The LWP is placed at the back of the appropriate queue regardless of whether the priority being set is different from the previous rt_pri value of the LWP. A running LWP can voluntarily release the CPU and go to the back of the scheduling queue at the same priority by resetting its rt_pri value to its current realtime priority value. To change the time quantum of an LWP without setting the priority or affecting the LWP's position on the queue, the rt_pri member should be set to the special value RT_NOCHANGE, defined in <sys/rtpriocntl.h>. Specifying RT_NOCHANGE when changing the class of an LWP to realtime from some other class results in the realtime priority being set to 0.

For the priocntl() PC_GETPARMS command, if pc_cid specifies the realtime class and more than one realtime LWP is specified, the scheduling parameters of the realtime LWP with the highest rt_pri value among the specified LWPs are returned and the LWP ID of this LWP is returned by the priocntl() call. If there is more than one LWP sharing the highest priority, the one returned is implementation-dependent.

The rt_tqsecs and rt_tqnsecs members are used for getting or setting the time quantum associated with an LWP or group of LWPs. rt_tqsecs is the number of seconds in the time quantum and rt_tqnsecs is the number of additional nanoseconds in the quantum. For example, setting rt_tqsecs to 2 and rt_tqnsecs to 500,000,000 (decimal) would result in a time quantum of two and one-half seconds. Specifying a value of 1,000,000,000 or greater in the rt_tqnsecs member results in an error return with errno set to EINVAL. Although the resolution of the tq_nsecs member is very fine, the specified time quantum length is rounded up by the system to the next integral multiple of the system clock's resolution. The maximum time quantum that can be specified is implementation-specific and equal to INT_MAX1 ticks. The INT_MAX value is defined in <limits.h>. Requesting a quantum greater than this maximum results in an error return with errno set to ERANGE, although infinite quantums can be requested using a special value as explained below. Requesting a time quantum of 0 by setting both rt_tqsecs and rt_tqnsecs to 0 results in an error return with errno set to EINVAL.

The rt_tqnsecs member can also be set to one of the following special values defined in <sys/rtpriocntl.h>, in which case the value of rt_tqsecs is ignored:

RT_TQINF

Set an infinite time quantum.

RT_TQDEF

Set the time quantum to the default for this priority (see rt_dptbl(4)).

RT_NOCHANGE

Do not set the time quantum. This value is useful when you wish to change the realtime priority of an LWP without affecting the time quantum. Specifying this value when changing the class of an LWP to realtime from some other class is equivalent to specifying RT_TQDEF.

When using the priocntl() PC_SETXPARMS or PC_GETXPARMS commands, the first argument after the command code must be the class name of the realtime class ("RT") . The next arguments are formed as (key, value) pairs, terminated by a 0 key. The definition for the keys of the realtime class can be found in <sys/rtpriocntl.h>. A repeated specification of the same key results in an error return and errno set to EINVAL.

When using the priocntl() PC_GETXPARMS command, the value associated with the key is always a pointer to a scheduling parameter of the value type shown in the table above. In contrast, when using the priocntl() PC_SETXPARMS command, the scheduling parameter is given as a direct value.

A priocntl() PC_SETXPARMS command with the class name ("RT") and without a following (key, value) pair will set or reset all realtime scheduling parameters of the target process(es) to their default values. Changing the class of an LWP to realtime from some other class causes the parameters to be set to their default values. The default realtime priority (RT_KY_PRI) is 0. A default time quantum (RT_TQDEF) is assigned to each priority class (see rt_dptbl(4)). The default realtime time quantum signal (RT_KY_TQSIG) is 0.

The value associated with RT_KY_TQSECS is the number of seconds in the time quantum. The value associated with RT_KY_TQNSECS is the number of nanoseconds in the quantum. Specifying a value of 1,000,000,000 or greater for the number of nanoseconds results in an error return and errno is set to EINVAL. The specified time quantum is rounded up by the system to the next integral multiple of the system clock's resolution. The maximum time quantum that can be specified is implementation-specific and equal to INT_MAX ticks, defined in <limits.h>. Requesting a quantum greater than this maximum results in an error return and errno is set to ERANGE. If seconds (RT_KY_TQSECS) but no nanoseconds (RT_KY_TQNSECS) are supplied, the number of nanoseconds is set to 0. If nanoseconds (RT_KY_TQNSECS) but no seconds (RT_KY_TQSECS) are supplied, the number of seconds is set to 0. A time quantum of 0 (seconds and nanoseconds are 0) results in an error return with errno set to EINVAL. Special values for RT_KY_TQSECS are RT_TQINF and RT_TQDEF (as described above). The priocntl() command PC_SETXPARMS knows no special value RT_NOCHANGE.

To change the class of an LWP to realtime from any other class, the LWP invoking priocntl() must have superuser privileges. To change the priority or time quantum setting of a realtime LWP, the LWP invoking priocntl() must have superuser privileges or must itself be a realtime LWP whose real or effective user ID matches the real of effective user ID of the target LWP.

The realtime priority and time quantum are inherited across fork(2) and the exec family of functions. When using the time quantum signal with a user-defined signal handler across the exec(2) system call, the new image must install an appropriate user-defined signal handler before the time quantum expires. Otherwise, unpredictable behavior might result.

The time-sharing scheduling policy provides for a fair and effective allocation of the CPU resource among LWPs with varying CPU consumption characteristics. The objectives of the time-sharing policy are to provide good response time to interactive LWPs and good throughput to CPU-bound jobs, while providing a degree of user/application control over scheduling.

The time-sharing class has a range of time-sharing user priority (see ts_upri below) values that can be assigned to LWPs within the class. A ts_upri value of 0 is defined as the default base priority for the time-sharing class. User priorities range from -x to +x where the value of x is configurable and can be determined for a specific installation by using the priocntl() PC_GETCID or PC_GETCLINFO command.

The purpose of the user priority is to provide some degree of user/application control over the scheduling of LWPs in the time-sharing class. Raising or lowering the ts_upri value of an LWP in the time-sharing class raises or lowers the scheduling priority of the LWP. It is not guaranteed, however, that an LWP with a higher ts_upri value will run before one with a lower ts_upri value, since the ts_upri value is just one factor used to determine the scheduling priority of a time-sharing LWP. The system can dynamically adjust the internal scheduling priority of a time-sharing LWP based on other factors such as recent CPU usage.

In addition to the system-wide limits on user priority (returned by the PC_GETCID and PC_GETCLINFO commands) there is a per LWP user priority limit (see ts_uprilim below) specifying the maximum ts_upri value that can be set for a given LWP. By default, ts_uprilim is 0.

A tsinfo_t structure with the following members, defined in <sys/tspriocntl.h>, defines the format used for the attribute data for the time-sharing class.

short ts_maxupri; /* Limits of user priority range */

The priocntl() PC_GETCID and PC_GETCLINFO commands return time-sharing class attributes in the pc_clinfo buffer in this format.

The ts_maxupri member specifies the configured maximum user priority value for the time-sharing class. If ts_maxupri is x, the valid range for both user priorities and user priority limits is from -x to +x.

A tsparms_t structure with the following members, defined in <sys/tspriocntl.h>, defines the format used to specify the time-sharing class-specific scheduling parameters of an LWP.

short ts_uprilim; /* Time-Sharing user priority limit */ short ts_upri; /* Time-Sharing user priority */

When using the priocntl() PC_SETPARMS or PC_GETPARMS commands, if pc_cid specifies the time-sharing class, the data in the pc_clparms buffer is in this format.

For the priocntl() PC_GETPARMS command, if pc_cid specifies the time-sharing class and more than one time-sharing LWP is specified, the scheduling parameters of the time-sharing LWP with the highest ts_upri value among the specified LWPs is returned and the LWP ID of this LWP is returned by the priocntl() call. If there is more than one LWP sharing the highest user priority, the one returned is implementation-dependent.

Any time-sharing LWP can lower its own ts_uprilim (or that of another LWP with the same user ID). Only a time-sharing LWP with superuser privileges can raise a ts_uprilim. When changing the class of an LWP to time-sharing from some other class, superuser privileges are required to set the initial ts_uprilim to a value greater than 0. Attempts by a non-superuser LWP to raise a ts_uprilim or set an initial ts_uprilim greater than 0 fail with a return value of -1 and errno set to EPERM.

Any time-sharing LWP can set its own ts_upri (or that of another LWP with the same user ID) to any value less than or equal to the LWP's ts_uprilim. Attempts to set the ts_upri above the ts_uprilim (and/or set the ts_uprilim below the ts_upri) result in the ts_upri being set equal to the ts_uprilim.

Either of the ts_uprilim or ts_upri members can be set to the special value TS_NOCHANGE, defined in <sys/tspriocntl.h>, to set one of the values without affecting the other. Specifying TS_NOCHANGE for the ts_upri when the ts_uprilim is being set to a value below the current ts_upri causes the ts_upri to be set equal to the ts_uprilim being set. Specifying TS_NOCHANGE for a parameter when changing the class of an LWP to time-sharing (from some other class) causes the parameter to be set to a default value. The default value for the ts_uprilim is 0 and the default for the ts_upri is to set it equal to the ts_uprilim that is being set.

When using the priocntl() PC_SETXPARMS or PC_GETXPARMS commands, the first argument after the command code is the class name of the time-sharing class ("TS") . The next arguments are formed as (key, value) pairs, terminated by a 0 key. The definition for the keys of the time-sharing class can be found in <sys/tspriocntl.h>. A repeated specification of the same key results in an error return and errno set to EINVAL.

When using the priocntl() PC_GETXPARMS command, the value associated with the key is always a pointer to a scheduling parameter of the value type in the table above. In contrast, when using the priocntl() PC_SETXPARMS command, the scheduling parameter is given as a direct value.

A priocntl() PC_SETXPARMS command with the class name ("TS") and without a following (key, value) pair will set or reset all time-sharing scheduling parameters of the target process(es) to their default values. Changing the class of an LWP to time-sharing from some other class causes the parameters to be set to their default values. The default value for the user priority limit (TS_KY_UPRILIM) is 0. The default value for the user priority (TS_KY_UPRI) is equal to the user priority limit (TS_KY_UPRILIM) that is being set.

The priocntl() command PC_SETXPARMS knows no special value TS_NOCHANGE.

The time-sharing user priority and user priority limit are inherited across fork() and the exec family of functions.

The fair-share scheduling policy provides a fair allocation of CPU resources among projects, independent of the number of processes they contain. Projects are given "shares" to control their quota of CPU resources. See FSS(7) for more information about how to configure shares.

The fair share class supports the notion of per-LWP user priority (see fs_upri below) values for compatibility with the time-sharing scheduling class. An fss_upri value of 0 is defined as the default base priority for the fair-share class. User priorities range from -x to +x where the value of x is configurable and can be determined for a specific installation by using the priocntl() PC_GETCID or PC_GETCLINFO command.

The purpose of the user priority is to provide some degree of user/application control over the scheduling of LWPs in the fair-share class. Raising the fss_upri value of an LWP in the fair-share class tells the scheduler to give this LWP more CPU time slices, while lowering the fss_upri value tells the scheduler to give it less CPU slices. It is not guaranteed, however, that an LWP with a higher fss_upri value will run before one with a lower fss_upri value. This is because the fss_upri value is just one factor used to determine the scheduling priority of a fair-share LWP. The system can dynamically adjust the internal scheduling priority of a fair-share LWP based on other factors such as recent CPU usage. The fair-share scheduler attempts to provide an evenly graded effect across the whole range of user priority values.

User priority values do not interfere with project shares. That is, changing a user priority value of a process does not have any effect on its project CPU entitlement, which is based on the number of shares it is allocated in comparison with other projects.

In addition to the system-wide limits on user priority (returned by the PC_GETCID and PC_GETCLINFO commands), there is a per-LWP user priority limit (see fs_uprilim below) that specifies the maximum fss_upri value that can be set for a given LWP. By default, fss_uprilim is 0.

A fssinfo_t structure with the following members, defined in <sys/fsspriocntl.h>, defines the format used for the attribute data for the fair-share class.

short    fss_maxupri;    /* Limits of user priority range */

The priocntl() PC_GETCID and PC_GETCLINFO commands return fair-share class attributes in the pc_clinfo buffer in this format.

fss_maxupri specifies the configured maximum user priority value for the fair-share class. If fss_maxupri is x, the valid range for both user priorities and user priority limits is from -x to +x.

A fssparms_t structure with the following members, defined in <sys/fsspriocntl.h>, defines the format used to specify the fair-share class-specific scheduling parameters of an LWP.

short    fss_uprilim;   /* Fair-share user priority limit */
short    fss_upri;      /* Fair-share user priority */

When using the priocntl() PC_SETPARMS or PC_GETPARMS commands, if pc_cid specifies the fair-share class, the data in the pc_clparms buffer is in this format.

For the priocntl() PC_GETPARMS command, if pc_cid specifies the fair-share class and more than one fair-share LWP is specified, the scheduling parameters of the fair-share LWP with the highest fs_upri value among the specified LWPs is returned and the LWP ID of this LWP is returned by the priocntl() call. If there is more than one LWP sharing the highest user priority, the one returned is implementation-dependent.

Any fair-share LWP can lower its own fss_uprilim (or that of another LWP with the same user ID). Only a fair-share LWP with superuser privileges can raise an fss_uprilim. When changing the class of an LWP to fair-share from some other class, superuser privileges are required to set the initial fss_uprilim to a value greater than 0. Attempts by a non-superuser LWP to raise an fs_uprilim or set an initial fs_uprilim greater than 0 fail with a return value of -1 and errno set to EPERM.

Any fair-share LWP can set its own fss_upri (or that of another LWP with the same user ID) to any value less than or equal to the LWP's fss_uprilim. Attempts to set the fss_upri above the fss_uprilim (and/or set the fss_uprilim below the fss_upri) result in the fss_upri being set equal to the fss_uprilim.

Either of the fss_uprilim or fss_upri members can be set to the special value FSS_NOCHANGE (defined in <sys/fsspriocntl.h>) to set one of the values without affecting the other. Specifying FSS_NOCHANGE for the fss_upri when the fss_uprilim is being set to a value below the current fss_upri causes the fss_upri to be set equal to the fss_uprilim being set. Specifying FSS_NOCHANGE for a parameter when changing the class of an LWP to fair-share (from some other class) causes the parameter to be set to a default value. The default value for the fss_uprilim is 0 and the default for the fss_upri is to set it equal to the fss_uprilim which is being set.

The fair-share user priority and user priority limit are inherited across fork() and the exec family of functions.

The fixed-priority class provides a fixed-priority preemptive scheduling policy for those LWPs requiring that the scheduling priorities do not get dynamically adjusted by the system and that the user/application have control of the scheduling priorities.

The fixed-priority class has a range of fixed-priority user priority (see fx_upri below) values that can be assigned to LWPs within the class. A fx_upri value of 0 is defined as the default base priority for the fixed-priority class. User priorities range from 0 to x where the value of x is configurable and can be determined for a specific installation by using the priocntl() PC_GETCID or PC_GETCLINFO command.

The purpose of the user priority is to provide user/application control over the scheduling of processes in the fixed-priority class. For processes in the fixed-priority class, the fx_upri value is, for all practical purposes, equivalent to the scheduling priority of the process. The fx_upri value completely determines the scheduling priority of a fixed-priority process relative to other processes within its class. Numerically higher fx_upri values represent higher priorities.

In addition to the system-wide limits on user priority (returned by the PC_GETCID and PC_GETCLINFO commands), there is a per-LWP user priority limit (see fx_uprilim below) that specifies the maximum fx_upri value that can be set for a given LWP. By default, fx_uprilim is 0.

A structure with the following member (defined in <sys/fxpriocntl.h>) defines the format used for the attribute data for the fixed-priority class.

pri_t   fx_maxupri;      /* Maximum user priority */

The priocntl() PC_GETCID and PC_GETCLINFO commands return fixed-priority class attributes in the pc_clinfo buffer in this format.

The fx_maxupri member specifies the configured maximum user priority value for the fixed-priority class. If fx_maxupri is x, the valid range for both user priorities and user priority limits is from 0 to x.

A structure with the following members (defined in <sys/fxpriocntl.h>) defines the format used to specify the fixed-priority class-specific scheduling parameters of an LWP.

pri_t    fx_upri;     /* Fixed-priority user priority */
pri_t    fx_uprilim;  /* Fixed-priority user priority limit */
uint_t   fx_tqsecs;   /* seconds in time quantum */
int      fx_tqnsecs;  /* additional nanosecs in time quant */

When using the priocntl() PC_SETPARMS or PC_GETPARMS commands, if pc_cid specifies the fixed-priority class, the data in the pc_clparms buffer is in this format.

For the priocntl() PC_GETPARMS command, if pc_cid specifies the fixed-priority class and more than one fixed-priority LWP is specified, the scheduling parameters of the fixed-priority LWP with the highest fx_upri value among the specified LWPs is returned and the LWP ID of this LWP is returned by the priocntl() call. If there is more than one LWP sharing the highest user priority, the one returned is implementation-dependent.

Any fixed-priority LWP can lower its own fx_uprilim (or that of another LWP with the same user ID). Only a fixed-priority LWP with superuser privileges can raise a fx_uprilim. When changing the class of an LWP to fixed-priority from some other class, superuser privileges are required to set the initial fx_uprilim to a value greater than 0. Attempts by a non-superuser LWP to raise a fx_uprilim or set an initial fx_uprilim greater than 0 fail with a return value of -1 and errno set to EPERM.

Any fixed-priority LWP can set its own fx_upri (or that of another LWP with the same user ID) to any value less than or equal to the LWP's fx_uprilim. Attempts to set the fx_upri above the fx_uprilim (and/or set the fx_uprilim below the fx_upri) result in the fx_upri being set equal to the fx_uprilim.

Either of the fx_uprilim or fx_upri members can be set to the special value FX_NOCHANGE (defined in <sys/fxpriocntl.h>) to set one of the values without affecting the other. Specifying FX_NOCHANGE for the fx_upri when the fx_uprilim is being set to a value below the current fx_upri causes the fx_upri to be set equal to the fx_uprilim being set. Specifying FX_NOCHANGE for a parameter when changing the class of an LWP to fixed-priority (from some other class) causes the parameter to be set to a default value. The default value for the fx_uprilim is 0 and the default for the fx_upri is to set it equal to the fx_uprilim that is being set. The default for time quantum is dependent on the fx_upri and on the system configuration; see fx_dptbl(4).

The fx_tqsecs and fx_tqnsecs members are used for getting or setting the time quantum associated with an LWP or group of LWPs. fx_tqsecs is the number of seconds in the time quantum and fx_tqnsecs is the number of additional nanoseconds in the quantum. For example, setting fx_tqsecs to 2 and fx_tqnsecs to 500,000,000 (decimal) would result in a time quantum of two and one-half seconds. Specifying a value of 1,000,000,000 or greater in the fx_tqnsecs member results in an error return with errno set to EINVAL. Although the resolution of the tq_nsecs member is very fine, the specified time quantum length is rounded up by the system to the next integral multiple of the system clock's resolution. The maximum time quantum that can be specified is implementation-specific and equal to INT_MAX ticks (defined in <limits.h>). Requesting a quantum greater than this maximum results in an error return with errno set to ERANGE, although infinite quantums can be requested using a special value as explained below. Requesting a time quantum of 0 (setting both fx_tqsecs and fx_tqnsecs to 0) results in an error return with errno set to EINVAL.

The fx_tqnsecs member can also be set to one of the following special values (defined in <sys/fxpriocntl.h>), in which case the value of fx_tqsecs is ignored:

FX_TQINF

Set an infinite time quantum.

FX_TQDEF

Set the time quantum to the default for this priority (see fx_dptbl(4)).

FX_NOCHANGE

Do not set the time quantum. This value is useful in changing the user priority of an LWP without affecting the time quantum. Specifying this value when changing the class of an LWP to fixed-priority from some other class is equivalent to specifying FX_TQDEF.

When using the priocntl() PC_SETXPARMS or PC_GETXPARMS commands, the first argument after the command code must be the class name of the fixed-priority class (FX) . The next arguments are formed as (key, value) pairs, terminated by a 0 key. The definition for the keys of the fixed-priority class can be found in <sys/fxpriocntl.h>. A repeated specification of the same key results in an error return and errno set to EINVAL.

When using the priocntl() PC_GETXPARMS command, the value associated with the key is always a pointer to a scheduling parameter of the value type shown in the table above. In contrast, when using the priocntl() PC_SETXPARMS command, the scheduling parameter is given as a direct value.

A priocntl() PC_SETXPARMS command with the class name (FX) and without a following (key, value) pair will set or reset all realtime scheduling parameters of the target process(es) to their default values. Changing the class of an LWP to fixed-priority from some other class causes the parameters to be set to their default values. The default value for the user priority limit (FX_KY_UPRILIM) is 0. The default value for the user priority (FX_KY_UPRI) is equal to the user priority limit (FX_KY_UPRILIM) that is being set. A default time quantum (FX_TQDEF) is assigned to each priority class (see fx_dptbl(4)).

The value associated with FX_KY_TQSECS is the number of seconds in the time quantum. The value associated with FX_KY_TQNSECS is the number of nanoseconds in the quantum. Specifying a value of 1,000,000,000 or greater for the number of nanoseconds results in an error return and errno is set to EINVAL. The specified time quantum is rounded up by the system to the next integral multiple of the system clock's resolution. The maximum time quantum that can be specified is implementation-specific and equal to INT_MAX ticks, defined in <limits.h>. Requesting a quantum greater than this maximum results in an error return and errno is set to ERANGE. If seconds (FX_KY_TQSECS) but no nanoseconds (FX_KY_TQNSECS) are supplied, the number of nanoseconds is set to 0. If nanoseconds (FX_KY_TQNSECS) but no seconds (FX_KY_TQSECS) are supplied, the number of seconds is set to 0. A time quantum of 0 (seconds and nanoseconds are 0) results in an error return with errno set to EINVAL. Special values for FX_KY_TQSECS are FX_TQINF and FX_TQDEF (as described above). The priocntl() command PC_SETXPARMS knows no special value FX_NOCHANGE.

The fixed-priority user priority and user priority limit are inherited across fork(2) and the exec family of functions (see exec(2)).

Unless otherwise noted above, priocntl() returns 0 on success. On failure, priocntl() returns -1 and sets errno to indicate the error.

The priocntl() function will fail if:

EAGAIN

An attempt to change the class of an LWP failed because of insufficient resources other than memory (for example, class-specific kernel data structures).

EFAULT

One of the arguments points to an illegal address.

EINVAL

The argument cmd was invalid, an invalid or unconfigured class was specified, or one of the parameters specified was invalid.

ENOMEM

An attempt to change the class of an LWP failed because of insufficient memory.

EPERM

The effective user of the calling LWP is not superuser.

ERANGE

The requested time quantum is out of range.

ESRCH

None of the specified LWPs exist.

priocntl(1), dispadmin(1M), init(1M), _lwp_create(2), exec(2), fork(2), nice(2), priocntlset(2), fx_dptbl(4), rt_dptbl(4)

System Administration Guide: Basic Administration

Programming Interfaces Guide