illumos: manual page: priocntl.2

PRIOCNTL(2) System Calls PRIOCNTL(2)

NAME

priocntl - process scheduler control

SYNOPSIS

#include <sys/types.h>
#include <sys/priocntl.h>
#include <sys/rtpriocntl.h>
#include <sys/tspriocntl.h>
#include <sys/iapriocntl.h>
#include <sys/fsspriocntl.h>
#include <sys/fxpriocntl.h>

long priocntl(idtype_t idtype, id_t id, int cmd, /* arg */ ...);

DESCRIPTION

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) function
and the exec(2) family of functions. 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.

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

P_CTID
The id argument is a process contract ID. The priocntl()
function applies to all LWPs with this process contract 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, project ID, zone ID, or process contract
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 the calling LWP must
have sufficient privileges. 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(8) 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, IA for interactive, FSS for fair-share, or FX for fixed-
priority. Each string is null-terminated.

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, INTERACTIVE CLASS, FAIR-SHARE 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, IA for interactive, FSS
for fair-share, 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 than
PC_SETPARMS and PC_GETPARMS and should replace PC_SETPARMS and
PC_GETPARMS on a long-term basis.

COMMANDS

Available priocntl() commands are:

PC_ADMIN
This command provides functionality needed for the
implementation of the dispadmin(8) 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>,
<sys/iapriocntl.h>, <sys/fsspriocntl.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>,
<sys/iapriocntl.h>, <sys/fsspriocntl.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>, <sys/iapriocntl.h>,
<sys/fsspriocntl.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>, <sys/iapriocntl.h>,
<sys/fsspriocntl.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>,
<sys/iapriocntl.h>, <sys/fsspriocntl.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().

REALTIME CLASS

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) 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_MAX 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(5)).

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.

+--------------+------------+------------------------------+
| Key | Value Type | Description |
+--------------+------------+------------------------------+
|RT_KY_PRI | pri_t | realtime priority |
|RT_KY_TQSECS | uint_t | seconds in time quantum |
+--------------+------------+------------------------------+
|RT_KY_TQNSECS | int | nanoseconds in time quantum |
+--------------+------------+------------------------------+
|RT_KY_TQSIG | int | realtime time quantum signal |
+--------------+------------+------------------------------+

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(5)). 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 sufficient privileges. To change the
priority or time quantum setting of a realtime LWP, the LWP invoking
priocntl() must have sufficient 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 functions, the new image must
install an appropriate user-defined signal handler before the time
quantum expires. Otherwise, unpredictable behavior might result.

TIME-SHARING CLASS
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 sufficient
privileges can raise a ts_uprilim. When changing the class of an LWP to
time-sharing from some other class, sufficient privileges are required to
set the initial ts_uprilim to a value greater than 0. Attempts by an
unprivileged 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.

+--------------+------------+---------------------+
| Key | Value Type | Description |
+--------------+------------+---------------------+
|TS_KY_UPRILIM | pri_t | user priority limit |
|TS_KY_UPRI | pri_t | user priority |
+--------------+------------+---------------------+

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.

INTERACTIVE CLASS

The interactive scheduling policy is a variation on the time-sharing
scheduling policy. All that can be said about the time-sharing scheduling
policy is also true for the interactive scheduling policy, with one
addition: An LWP in the interactive class with its ia_mode value set to
IA_SET_INTERACTIVE has its time-sharing priority boosted by IA_BOOST
(10).

An iainfo_t structure with the following members, defined in
<sys/iapriocntl.h>, defines the format used for the attribute data for
the interactive class.

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

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

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

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

short ia_uprilim; /* Interactive user priority limit */
short ia_upri; /* Interactive user priority */
int ia_mode; /* interactive on/off */

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

For the priocntl() PC_GETPARMS command, if pc_cid specifies the
interactive class and more than one interactive LWP is specified, the
scheduling parameters of the interactive LWP with the highest ia_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.

All that is said above in the TIME-SHARING CLASS section concerning
manipulation of ts_uprilim and ts_upri applies equally to manipulations
of ia_uprilim and ia_upri in the interactive class.

When using the PC_SETPARMS command, the ia_mode member must be set to one
of the values IA_SET_INTERACTIVE, IA_INTERACTIVE_OFF, or IA_NOCHANGE,
defined in <sys/iapriocntl.h>, to set the interactive mode on or off or
to make no change to the interactive mode.

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

Key Value Type Description
IA_KY_UPRILIM pri_t user priority limit
IA_KY_UPRI pri_t user priority
IA_KY_MODE int interactive mode

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 (IA) and without a
following (key, value) pair will set or reset all interactive scheduling
parameters of the target process(es) to their default values. Changing
the class of an LWP to interactive from some other class causes the
parameters to be set to their default values. The default value for the
user priority limit (IA_KY_UPRILIM) is 0. The default value for the user
priority (IA_KY_UPRI) is equal to the user priority limit (IA_KY_UPRILIM)
that is being set. The default value for the interactive mode
(IA_KY_MODE) is IA_SET_INTERACTIVE.

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

The interactive user priority and user priority limit are inherited
across fork and the exec family of functions.

FAIR-SHARE CLASS
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(4) for more information about how to configure shares.

The fair share class supports the notion of per-LWP user priority (see
fss_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 fss_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 fss_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 sufficient privileges
can raise an fss_uprilim. When changing the class of an LWP to fair-share
from some other class, sufficient privileges are required to enter the
FSS class or to set the initial fss_uprilim to a value greater than 0.
Attempts by an unprivileged LWP to raise an fss_uprilim or set an initial
fss_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.

FIXED-PRIORITY CLASS
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 sufficient
privileges can raise a fx_uprilim. When changing the class of an LWP to
fixed-priority from some other class, sufficient privileges are required
to set the initial fx_uprilim to a value greater than 0. Attempts by an
unprivileged 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(5).

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(5)).

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.

+--------------+------------+-----------------------------+
| Key | Value Type | Description |
+--------------+------------+-----------------------------+
|FX_KY_UPRILIM | pri_t | user priority limit |
|FX_KY_UPRI | pri_t | user priority |
+--------------+------------+-----------------------------+
|FX_KY_TQSECS | uint_t | seconds in time quantum |
+--------------+------------+-----------------------------+
|FX_KY_TQNSECS | int | nanoseconds in time quantum |
+--------------+------------+-----------------------------+

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(5)).

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.

RETURN VALUES

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

ERRORS

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 {PRIV_PROC_PRIOCNTL} privilege is not asserted in the
effective set of the calling LWP.

The calling LWP does not have sufficient privileges to affect
the target LWP.

ERANGE
The requested time quantum is out of range.

ESRCH
None of the specified LWPs exist.