SchedCtl(), SchedCtl_r()

Control the scheduler

Synopsis:

#include <sys/sched_aps.h>
#include <sys/neutrino.h>

int SchedCtl( int cmd,
              void *data,
              int length);

int SchedCtl_r( int cmd,
                void *data,
                int length);

Arguments:

cmd
The control command that you want to execute; one of:

If you've loaded the adaptive partitioning module into your OS image, the following commands are also available:

data
A pointer to the specific data structure for the command.
length
The size of the structure that data points to.

For details about each command and its data, see the sections below.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The SchedCtl() and SchedCtl_r() kernel calls control the scheduler. These functions are identical except in the way they indicate errors; see the Returns section for details.

Note:

The adaptive partitioning scheduler is optional and is present only if you add [module=aps] to your OS image's buildfile. For more information, see the Adaptive Partitioning User's Guide.

For the control commands that are related to adaptive partitioning, you must initialize all of the fields—including reserved ones—in the structures you pass as the data argument, by calling (for example) memset(). You can also use the APS_INIT_DATA() macro: 

APS_INIT_DATA( &data );

SCHED_APS_QUERY_PARMS

This command fills in a sched_aps_info structure that describes the overall parameters of the adaptive partitioning scheduler: 

typedef struct {
    uint64_t        cycles_per_ms;
    uint64_t        windowsize_cycles;   /* Deprecated */
    uint64_t        windowsize2_cycles;  /* Deprecated */
    uint64_t        windowsize3_cycles;  /* Deprecated */
    uint32_t        scheduling_policy_flags;
    uint32_t        sec_flags;
    uint32_t        bankruptcy_policy;
    uint16_t        num_partitions;
    uint16_t        max_partitions;
    uint16_t        windowsize_ms;
    uint16_t        reserved1;       
    uint32_t        reserved2;
    uint64_t        reserved3;
} sched_aps_info;

The members include:

cycles_per_ms
The number of machine cycles in a millisecond. Use this value to convert the output of the SCHED_APS_QUERY_PARTITION command to the time units of your choice.
Note:
The value of cycles_per_ms:
  • might not equal the value of the cycles_per_sec member of the system page divided by 1000
  • isn't necessarily in the same units as values returned by ClockCycles() on all platforms
scheduling_policy_flags
The set of SCHED_APS_SCHEDPOL_* flags that describe the scheduling policy. For more information, see Scheduling policies, below.
sec_flags
The set of SCHED_APS_SEC_* flags that describe the security options. For more information, see Security, below.
bankruptcy_policy
What to do if a partition exhausts its critical budget; a combination of SCHED_APS_BNKR_* flags (see Handling bankruptcy, below).
num_partitions
The number of partitions defined.
max_partitions
The largest number of partitions that may be created at any time.
windowsize_ms
The length of the averaging window used for scheduling, in milliseconds.

Scheduling policies

These flags set options for the adaptive partitioning scheduling algorithm. To set, pass a pointer to an ORed set of these flags with the SCHED_APS_SET_PARMS call to SchedCtl():

SCHED_APS_SCHEDPOL_FREETIME_BY_RATIO
Free time is when at least one partition isn't running. Its time becomes free to other partitions that may then run over their budgets.

By default, the scheduler hands out free time to the partition with the highest-priority running thread. That guarantees realtime scheduling behavior (i.e., scheduling strictly by priority) to partitions any time they aren't being limited by some other partition's right to its guaranteed minimum budget. But it also means that one partition is allowed to grab all the free time.

If you set SCHED_APS_SCHEDPOL_FREETIME_BY_RATIO, the running partitions share the free time in proportion to the ratios of their budgets. So, one partition can no longer grab all the free time. However, when this flag is set, partitions will see strict priority-scheduling between partitions only when they're consuming less than their CPU budgets.

SCHED_APS_SCHEDPOL_DEFAULT
The default policy, which currently means that SCHED_APS_SCHEDPOL_FREETIME_BY_RATIO isn't set, long-window reporting is enabled, and all maximum budgets are 100%. QNX Neutrino sets this at startup.
SCHED_APS_SCHEDPOL_PARTITION_LOCAL_PRIORITIES
Normally, the APS scheduler always selects the highest-priority thread from partitions with available budget. That algorithm produces behavior closest to realtime scheduling. In particular, it allows the highest-priority partition to run to completion (as long as it keeps under its budget).

Allowing the highest-priority partition to run to completion means lower-priority partitions won't run in the meantime. That means that when the system is loaded, the default algorithm can cause small-budget low-priority partitions to see long delays between intervals when they run. (For example, on a loaded system with a 100 ms averaging window, a 10% partition may run only every 90 milliseconds.) One way to reduce the latency is to reduce the averaging window size.

The SCHED_APS_SCHEDPOL_PARTITION_LOCAL_PRIORITIES policy schedules purely by budget ratio. When enabled, the scheduler tries to balance budgets on as short a timescale as possible, regardless of the window size.

That means high-priority partitions with large budgets no longer run to completion (while they have budget). They're timesliced with other partitions, even low-priority ones. The result is that SCHED_APS_SCHEDPOL_PARTITION_LOCAL_PRIORITIES can reduce the latencies seen by small budget partitions in a loaded system. This comes at the cost of a departure from strict priority preemptive behavior when all partitions have budget (i.e., the default policy).

The SCHED_APS_SCHEDPOL_PARTITION_LOCAL_PRIORITIES policy provides the latencies while retaining the full accuracy of a 100 ms averaging window. It continues to schedule the highest priority thread within partitions.

This option includes the behavior of SCHED_APS_SCHEDPOL_FREETIME_BY_RATIO.

When a critical thread consumes critical time, it temporarily forces a return to the default scheduling policy. Critical threads are allowed to run to completion and aren't timesliced by SCHED_APS_SCHEDPOL_PARTITION_LOCAL_PRIORITIES's attempts to balance budgets. In other words, critical threads aren't affected by this policy.

Note:
Don't use this scheduling policy if you have running threads in a zero-budget partition. Since this policy divides time by the ratio of budgets, a zero-budget partition may never be scheduled.
SCHED_APS_SCHEDPOL_LIMIT_CPU_USAGE
Enable enforcement of the max_budget_percent parameters, which limit the amount a partition can overrun its normal budget when the system is underloaded. If this option isn't set, max_budget_percent is ignored when you're setting parameters, and is reported as 100% (meaning no limit on freetime usage).
Note:
Threads in a partition with a normal budget of 0 and a max_budget_percent of 0 will never run.

Scheduling within a partition is always strictly by priority, no matter which of these flags are set.

For more information about adaptive partitioning and BMP, see the Adaptive Partitioning Scheduling Details chapter of the Adaptive Partitioning User's Guide.

Handling bankruptcy

Bankruptcy is when critical CPU time billed to a partition exceeds its critical budget. Bankruptcy is always considered to be a design error on the part of the application, but you can configure how the system responds to it.

If the system isn't declaring bankruptcy when you expect it, note that bankruptcy can be declared only if critical time is billed to your partition. Critical time is billed on those timeslices when the following conditions are all met:

  • The partition of the running thread has a critical budget greater than zero.
  • The running thread has a critical priority.
  • The partition must be out of percentage-CPU budget.
  • There be at least one other partition that is competing for CPU time.

Only then if the critical time, billed over the current averaging window, exceeds a partition's critical budget will the system declare the partition bankrupt.

When the system detects that a partition has gone bankrupt:

  1. It causes that partition to be out-of-budget for the remainder of the current scheduling window.
  2. If you've set a sigevent via procmgr_event_notify() or procmgr_event_notify_add() with a flag of PROCMGR_EVENT_APS_BANKRUPTCY, the system delivers the event.

In addition, you can configure the following responses:

SCHED_APS_BNKR_BASIC
Deliver bankruptcy-notification events and make the partition out-of-budget for the rest of the scheduling window (nominally 100 ms). This is the default.
SCHED_APS_BNKR_CANCEL_BUDGET
Set the offending partition's critical budget to zero, which forces the partition to be scheduled by its percentage CPU budget only. This also means that a second bankruptcy can't occur. This persists until a restart occurs, or you call SCHED_APS_MODIFY_PARTITION to set a new critical budget.
SCHED_APS_BNKR_REBOOT
Cause the system to crash with a brief message identifying the offending partition. This is the most severe response, suggested for use while testing a product, to make sure bankruptcies are never ignored. You probably shouldn't use this option in your finished product.

To set a choice of bankruptcy-handling options, OR the above SCHED_APS_BNKR_* flags and pass a pointer to it as the bankruptcy_policyp field of the sched_aps_parms structure when you call SCHED_APS_SET_PARMS.

Errors:

SchedCtl() and SchedCtl_r() indicate the following errors for the SCHED_APS_QUERY_PARMS command (see the Returns section for details):

EOK
Success.
EACCES
The calling thread doesn't meet the security options set (see SCHED_APS_ADD_SECURITY). Your process must have the PROCMGR_AID_APS_ROOT ability (see procmgr_ability()).
EDOM
A reserved field isn't zero. You might not have used APS_INIT_DATA() to initialize the data parameter.
EINVAL
The size of the parameter block doesn't match the size of the expected structure.
ENOSYS
The adaptive partitioning scheduler isn't installed.

SCHED_APS_SET_PARMS

This command sets the parameters for the overall behavior of the adaptive partitioning scheduler. The data argument must be a pointer to a sched_aps_parms structure: 

typedef struct { 
    int16_t windowsize_ms;
    int16_t     reserved1;
    uint32_t    *scheduling_policy_flagsp;
    uint32_t    *bankruptcy_policyp;
    int32_t     reserved2;
    int64_t     reserved3;
} sched_aps_parms;

The members include:

windowsize_ms
The time over which the scheduler is to average CPU cycles and balance the partitions to their budgets as specified by SCHED_APS_CREATE_PARTITION. The default is 100 ms. If you don't want to set the window size, set this member to -1.
scheduling_policy_flagsp
A pointer to an ORed set of SCHED_APS_SCHEDPOL_* flags that specify the scheduling policy. For more information, see Scheduling policies, above. If you don't want to change the scheduling policy, set this member to NULL.
bankruptcy_policyp
A pointer to an ORing of SCHED_APS_BNKR_* flags, as described under Handling bankruptcy, above. If you don't want to change these flags, set this member to NULL.

Errors:

SchedCtl() and SchedCtl_r() indicate the following errors for the SCHED_APS_SET_PARMS command (see the Returns section for details):

EOK
Success.
EACCES
One of the following:
  • SCHED_APS_SEC_PARTITIONS_LOCKED is set.
  • SCHED_APS_SEC_ROOT0_OVERALL is set, and you aren't running in the System partition with the PROCMGR_AID_APS_ROOT ability (see procmgr_ability()).

For more information, see Security, below.

EDOM
A reserved field isn't zero. You might not have used APS_INIT_DATA() to initialize the data parameter.
EINVAL
The size of the parameter block doesn't match the size of the expected structure.
ENOSYS
The adaptive partitioning scheduler isn't installed.

SCHED_APS_CREATE_PARTITION

This command creates a new partition that's considered to be a child of the partition that's calling SchedCtl(). The system automatically creates a partition called System (the value of APS_SYSTEM_PARTITION_NAME) with an ID of 0.

The data argument for this command must be a pointer to a sched_aps_create_parms structure: 

typedef struct {
    /* input parms */ 
    char        *name;
    uint16_t    budget_percent;
    int16_t     critical_budget_ms;
    uint8_t     aps_create_flags;
    int8_t      parent_id;
    uint16_t    max_budget_percent;
    uint16_t    critical_priority;
    uint16_t    budget_percent_scale;
    uint64_t    reserved1;
    uint32_t    reserved2;
    /* output parms */
    int16_t     id;
    int16_t     reserved3;
} sched_aps_create_parms;

The input members include:

name
The name of the new partition. If name is NULL or points to an empty string, the partition's name is the same as its ID. The name must be no longer than APS_PARTITION_NAME_LENGTH, not including the trailing null character, can't start with a digit, and can't include any slashes (/).
budget_percent
The percentage CPU budget for the new partition. Budgets given to the new partition are subtracted from the parent partition.
Note:
Before creating zero-budget partitions, read the cautions in Setting budgets for resource managers in the System Considerations chapter of the Adaptive Partitioning User's Guide.
critical_budget_ms
The critical budget, in milliseconds, for the partition, or -1 or 0 if you don't want the partition to have a critical budget. Critical budgets don't affect the parent, but are automatically limited to be no bigger than the window size.
aps_create_flags
Flags that control the creation of the partition. The only flag currently defined is:
  • APS_CREATE_FLAGS_USE_PARENT_ID — if set, the parent_id field is used; otherwise it's ignored.
parent_id
Which partition the budget should come from. If -1, then the budget comes from the calling thread's budget.
max_budget_percent
The maximum CPU time, in percent, that the partition may consume if it has no competition (i.e., free time). This limit has an effect only if SCHED_APS_SCHEDPOL_LIMIT_CPU_USAGE is set.
critical_priority
Threads at this priority or higher are critical. This value is optional; set it to -1 or 0 to disable.
budget_percent_scale
The number of digits to the right of the decimal point in budget_percent and max_budget_percent. The budget is calculated as follows:

Actual Budget (%) = budget_percent / (10 ^ budget_percent_scale)

The output members include:

id
The created partition's ID number, in the range 0 to the maximum number of partitions − 1 (see the max_partitions member of the data from a call to SCHED_APS_QUERY_PARMS. The System partition's ID number is APS_SYSTEM_PARTITION_ID.

Errors:

SchedCtl() and SchedCtl_r() indicate the following errors for the SCHED_APS_CREATE_PARTITION command (see the Returns section for details):

EOK
Success.
EACCES
SCHED_APS_SEC_PARTITIONS_LOCKED is set, or any of these security conditions are set and not satisfied:
  • SCHED_APS_SEC_ROOT_MAKES_PARTITIONS
  • SCHED_APS_SEC_SYS_MAKES_PARTITIONS
  • SCHED_APS_SEC_NONZERO_BUDGETS
  • SCHED_APS_SEC_ROOT_MAKES_CRITICAL
  • SCHED_APS_SEC_SYS_MAKES_CRITICAL

For more information, see Security, below.

EDOM
A reserved field isn't zero. You might not have used APS_INIT_DATA() to initialize the data parameter.
EDQUOT
The parent partition doesn't have enough budget.
EEXIST
Another partition is already using the given name.
EINVAL
The size of the parameter block doesn't match the size of the expected structure, the partition name is badly formed, or the budget is out of range.
ENAMETOOLONG
The partition name is longer than APS_PARTITION_NAME_LENGTH characters.
ENOSPC
The maximum number of partitions already exist.
ENOSYS
The adaptive partitioning scheduler isn't installed.

SCHED_APS_QUERY_PARTITION

This command gets information about a given partition. The data argument for this command must be a pointer to a sched_aps_partition_info structure: 

typedef struct { 
    /* out parms */ 
    uint64_t    budget_cycles;   /* Deprecated */      
    uint64_t    critical_budget_cycles; 
    char        name[APS_PARTITION_NAME_LENGTH+1]; 
    int16_t     parent_id;
    uint16_t    budget_percent;     
    int32_t     notify_pid;      /* Deprecated */      
    int32_t     notify_tid;      /* Deprecated */      
    uint32_t    pinfo_flags;     /* Deprecated */      
    int32_t     pid_at_last_bankruptcy;
    int32_t     tid_at_last_bankruptcy;
    uint16_t    max_budget_percent;
    uint16_t    critical_priority;
    uint16_t    budget_percent_scale;
    int16_t     reserved1;
    int64_t     reserved2;
    /* input parm */
    int16_t     id;
} sched_aps_partition_info;

The input members include:

id
The number of the partition you want to query.

The output members include:

critical_budget_cycles
The critical budget, in cycles. To convert this value to milliseconds, multiply it by the cycles_per_ms value from a SCHED_APS_QUERY_PARMS command.
name
The name of the partition.
parent_id
The number of the partition that's the parent of the partition being queried. The System partition's ID number is APS_SYSTEM_PARTITION_ID.
budget_percent
The partition's budget, expressed as a percentage.
pid_at_last_bankruptcy, tid_at_last_bankruptcy
The process and thread IDs at the time of the last bankruptcy, or -1 if there wasn't a previous bankruptcy.
max_budget_percent
The maximum CPU time, in percent, that the partition may consume if it has no competition (i.e., free time). This is always reported as 100% if SCHED_APS_SCHEDPOL_LIMIT_CPU_USAGE isn't set.
critical_priority
Threads at this priority or higher are critical.
budget_percent_scale
The number of digits to the right of the decimal point in budget_percent and max_budget_percent.

Errors:

SchedCtl() and SchedCtl_r() indicate the following errors for the SCHED_APS_QUERY_PARTITION command (see the Returns section for details):

EOK
Success.
EDOM
A reserved field isn't zero. You might not have used APS_INIT_DATA() to initialize the data parameter.
EINVAL
The size of the parameter block doesn't match the size of the expected structure.
ENOSYS
The adaptive partitioning scheduler isn't installed.

SCHED_APS_LOOKUP

This command finds the partition ID for a given partition name.

The data argument for this command must be a sched_aps_lookup_parms structure: 

typedef struct {
        /* input parms */ 
        char    *name;
        int16_t reserved1;
        /* output parms */
        int16_t     id;
} sched_aps_lookup_parms;

The input members include:

name
The name of the partition.

The output members include:

id
The ID number of the partition, if found.

Errors:

SchedCtl() and SchedCtl_r() indicate the following errors for the SCHED_APS_LOOKUP command (see the Returns section for details):

EOK
Success.
EDOM
A reserved field isn't zero. You might not have used APS_INIT_DATA() to initialize the data parameter.
EINVAL
The name wasn't found.

SCHED_APS_JOIN_PARTITION

This command makes the thread specified by the given process and thread IDs becomes a member of the specified partition. This partition also becomes the thread's new home partition, i.e., where it returns after partition inheritance.

The data argument for this command must be a pointer to a sched_aps_join_parms structure: 

typedef struct { 
        int16_t     id; 
        int16_t     reserved1;
        int32_t     pid;
        int32_t     tid;
        int32_t     aid;
} sched_aps_join_parms;

The members include:

id
The ID number of the partition that the thread is to join.
pid, tid
The process and thread IDs of the thread that you want to join the specified partition:
  • If both pid and tid are zero, the calling thread joins the specified partition.
  • If tid is -1, the process with ID pid joins the partition. This doesn't change the partitions that the process's threads are in; it just sets the partition that the threads run in when they're handling a pulse.

    If tid is -2, then the partition in which pulses are handled is changed, plus all threads in the given process are joined to the target partition.

aid
If non-zero, join all processes for this application ID. For more information, see "Application groups" in the QNX Neutrino System Security Guide.

Errors:

SchedCtl() and SchedCtl_r() indicate the following errors for the SCHED_APS_JOIN_PARTITION command (see the Returns section for details):

EOK
Success.
EACCES
The following security options are set but not satisfied:
  • SCHED_APS_SEC_ROOT_JOINS
  • SCHED_APS_SEC_SYS_JOINS
  • SCHED_APS_SEC_PARENT_JOINS
  • SCHED_APS_SEC_JOIN_SELF_ONLY

For more information, see Security, below.

EDOM
A reserved field isn't zero. You might not have used APS_INIT_DATA() to initialize the data parameter.
EINVAL
One of the following occurred:
  • The size of the parameter block doesn't match the size of the expected structure, or the partition with the given ID doesn't exist.
  • The adaptive partitioning scheduler isn't installed.
ESRCH
The pid and tid are invalid.

SCHED_APS_MODIFY_PARTITION

This command changes the parameters of an existing partition. If the new budget's value is different from the current, the difference is either taken from, or returned to, the parent partition's budget. The critical time parameter affects only the chosen partition, not its parent. To change just one of new budget or new critical time, set the other to -1.

Note:
  • You can't use this command to modify the System partition's budget. To increase the size of the System partition, reduce the budget of one of its child partitions.
  • Reducing the size of a partition may cause it not to run for the time of an averaging window, as you may have caused it to become temporarily over-budget. However, reducing the critical time doesn't trigger the declaration of bankruptcy.

The data argument for this command must be a pointer to a sched_aps_modify_parms structure: 

typedef struct { 
        int16_t     id;
        int16_t     new_budget_percent;
        int16_t     new_critical_budget_ms;
        int16_t     new_max_budget_percent;
        int16_t     new_critical_priority;
        uint16_t    budget_percent_scale;
        int32_t     reserved1;
        int64_t     reserved2;
} sched_aps_modify_parms;

The members include:

id
The ID number of the partition.
new_budget_percent
The new budget for the partition, expressed as a percentage, or -1 if you don't want to change it.
new_critical_budget_ms
The new critical budget, in milliseconds, for the partition, or -1 if you don't want to change it. If the critical budget is greater than the window size, it's considered to be infinite.
max_budget_percent
The maximum CPU time, in percent, that the partition may consume if it has no competition (i.e., free time). This limit has an effect only if SCHED_APS_SCHEDPOL_LIMIT_CPU_USAGE is set.
critical_priority
Threads at this priority or higher are critical. This value is optional; set it to -1 or 0 to skip.
budget_percent_scale
The number of digits to the right of the decimal point in new_budget_percent and max_budget_percent.

Errors:

SchedCtl() and SchedCtl_r() indicate the following errors for the SCHED_APS_MODIFY_PARTITION command (see the Returns section for details):

EOK
Success.
EACCES
SCHED_APS_SEC_PARTITIONS_LOCKED is set, or the following security options are set and not satisfied:
  • SCHED_APS_SEC_PARENT_MODIFIES
  • SCHED_APS_SEC_ROOT_MAKES_PARTITIONS
  • SCHED_APS_SEC_SYS_MAKES_PARTITIONS
  • SCHED_APS_SEC_NONZERO_BUDGETS
  • SCHED_APS_SEC_ROOT_MAKES_CRITICAL
  • SCHED_APS_SEC_SYS_MAKES_CRITICAL

For more information, see Security, below.

EDOM
A reserved field isn't zero. You might not have used APS_INIT_DATA() to initialize the data parameter.
EINVAL
The size of the parameter block doesn't match the size of the expected structure, or the partition with the given ID doesn't exist.
ENOSYS
The adaptive partitioning scheduler isn't installed.

SCHED_APS_PARTITION_STATS

This command returns instantaneous values of the CPU time-accounting variables for a set of partitions. It can fill in data for more than one partition. If the length argument to SchedCtl() indicates that you've passed the function an array of sched_aps_partition_stats structures, SchedCtl() fills each element with statistics for a different partition, starting with the partition specified by the id field.

Note:
To get an accurate picture for the whole machine it's important to read data for all partitions in one call, since sequential calls to SCHED_APS_PARTITION_STATS may come from separate averaging windows.

To determine the number of partitions, use the SCHED_APS_OVERALL_STATS command.

The command overwrites the id field with the partition number for which data is being returned. It stores -1 in the id field of unused elements.

To convert times in cycles into milliseconds, divide them by the cycles_per_ms obtained with an SCHED_APS_QUERY_PARMS command.

The data argument for this command must be a pointer to a sched_aps_partition_stats structure, or an array of these structures: 

typedef struct { 
    /* out parms */ 
    uint64_t        run_time_cycles;
    uint64_t        critical_time_cycles;
    uint64_t        run_time_cycles_w2;        /* Deprecated */
    uint64_t        critical_time_cycles_w2;   /* Deprecated */
    uint64_t        run_time_cycles_w3;        /* Deprecated */
    uint64_t        critical_time_cycles_w3;   /* Deprecated */
    uint32_t        stats_flags;
    uint32_t        reserved1;
    uint64_t        dynamic_windowsize_cycles;	/* length of last averaging window used for scheduling */
    uint64_t        reserved2;
    /* in parm */
    int16_t     id;
} sched_aps_partition_stats;

The members include:

run_time_cycles
The CPU execution time during the last scheduling window.
critical_time_cycles
The time billed as critical during the last scheduling window.
stats_flags
A set of the following flags:
  • SCHED_APS_PSTATS_IS_BANKRUPT_NOW — the critical time used is greater than the critical budget at the time you used the SCHED_APS_PARTITION_STATS command.
  • SCHED_APS_PSTATS_WAS_BANKRUPT — the partition was declared bankrupt sometime since the last restart.
dynamic_windowsize_cycles
The length of last averaging window used for scheduling. Note that dynamic_windowsize_cycles may differ from the nominal window size. Use dynamic_windowsize_cycles to convert run_time_cycles to a percentage.
id
This is both an input and output field. As input, it's the ID number of the first partition you want data for. If you've passed an array of sched_aps_partition_stats structures, the command fills in the ID number for each partition that it fills in statistics for.

Errors:

SchedCtl() and SchedCtl_r() indicate the following errors for the SCHED_APS_PARTITION_STATS command (see the Returns section for details):

EOK
Success.
EDOM
A reserved field isn't zero. You might not have used APS_INIT_DATA() to initialize the data parameter.
EINVAL
The size of the parameter block isn't a multiple of size(sched_aps_partition_stats).
ENOSYS
The adaptive partitioning scheduler isn't installed.

SCHED_APS_OVERALL_STATS

This command returns instantaneous information about scheduler states. The data argument for this command must be a pointer to a sched_aps_overall_stats structure: 

typedef struct { 
        uint64_t    idle_cycles;     /* Deprecated */
        uint64_t    idle_cycles_w2;  /* Deprecated */
        uint64_t    idle_cycles_w3;  /* Deprecated */
        int16_t     id_at_last_bankruptcy;
        uint16_t    reserved1;
        int32_t     pid_at_last_bankruptcy;
        int32_t     tid_at_last_bankruptcy;
        uint32_t    reserved2;
        uint32_t    reserved3;
        uint64_t    reserved4;
} sched_aps_overall_stats;

The members include:

id_at_last_bankruptcy
The ID of last bankrupt partition, or -1 if no bankruptcy has occurred.
pid_at_last_bankruptcy, tid_at_last_bankruptcy
The process and thread IDs at last the bankruptcy, or -1 if no bankruptcy has occurred.

Errors:

SchedCtl() and SchedCtl_r() indicate the following errors for the SCHED_APS_OVERALL_STATS command (see the Returns section for details):

EOK
Success.
EDOM
A reserved field isn't zero. You might not have used APS_INIT_DATA() to initialize the data parameter.
EINVAL
The size of the parameter block doesn't match the size of the expected structure.
ENOSYS
The adaptive partitioning scheduler isn't installed.

SCHED_APS_QUERY_THREAD

This command determines the partition for the given thread and indicates whether or not the thread in your process is marked to run as critical. Use a thread ID of zero to indicate the calling thread.

The data argument for this command must be a pointer to a sched_aps_query_thread_parms structure: 

typedef struct { 
        int32_t     pid;
        int32_t     tid;
        /* out parms: */
        int16_t     id;
        int16_t     inherited_id;
        uint32_t    crit_state_flags;
        int32_t     reserved1;
        int32_t     reserved2;
} sched_aps_query_thread_parms;

The input members include:

pid
The ID of process that the thread belongs to, or 0 to indicate the calling process.
tid
The thread ID, or 0 for the calling thread.

The output members include:

id
The ID number of the partition that the thread originally joined.
inherited_id
The ID number of the partition that the thread currently belongs to. This might not be the same as the id member, because the thread might have inherited the partition from a calling process.
crit_state_flags
A combination of the following flags:
  • APS_QCRIT_RUNNING_CRITICAL — the thread is currently running as critical.
  • APS_QCRIT_BILL_AS_CRITICAL — the thread's execution time is being billed to the partition's critical budget.

Errors:

SchedCtl() and SchedCtl_r() indicate the following errors for the SCHED_APS_QUERY_THREAD command (see the Returns section for details):

EOK
Success.
EDOM
A reserved field isn't zero. You might not have used APS_INIT_DATA() to initialize the data parameter.
EINVAL
The size of the parameter block doesn't match the size of the expected structure.
ENOSYS
The adaptive partitioning scheduler isn't installed.
ESRCH
The specified thread wasn't found.

SCHED_APS_ADD_SECURITY

This command sets security options. A bit that's set turns the corresponding security option on. Successive calls add to the existing set of security options. Security options can be cleared only by a restart.

Note:
You must be running in the System partition with the PROCMGR_AID_APS_ROOT ability enabled (see procmgr_ability()) in order to use this command, even if all security options are off.

The data argument for this command must be a pointer to a sched_aps_security_parms structure: 

typedef struct {
        uint32_t        sec_flags;
        uint32_t        reserved1;
        uint32_t        reserved2;
} sched_aps_security_parms;

The members include:

sec_flags
A set of SCHED_APS_SEC_* flags (see below), as both input and output parameters. Set this member to 0 if you want to get the current security flags.

Security

The adaptive partitioning scheduler lets you dynamically create and modify the partitions in your system.

Note:
We recommend that you set up your partition environment at boot time, and then lock all parameters:
  • in a program, by using the SCHED_APS_SEC_PARTITIONS_LOCKED flag
  • from the command line, by using the aps modify command

However you might need to modify a partition at runtime. In this case, you can use the security options described below.

When QNX Neutrino starts, it sets the security option to SCHED_APS_SEC_OFF. We recommend that you immediately set it to SCHED_APS_SEC_RECOMMENDED. In code, do this: 

sched_aps_security_parms p;

APS_INIT_DATA( &p );
p.sec_flags = SCHED_APS_SEC_RECOMMENDED;
SchedCtl( SCHED_APS_ADD_SECURITY,&p, sizeof(p) );
Note:
Some of the security options restrict certain operations to processes that have the PROCMGR_AID_APS_ROOT ability enabled (see procmgr_ability()).

The security options include the following:

SCHED_APS_SEC_RECOMMENDED
Only a process that's running in the System partition with the PROCMGR_AID_APS_ROOT ability enabled may create partitions or change parameters. This arranges a 2-level hierarchy of partitions: the System partition and its children. Only a process that's running in the System partition with the PROCMGR_AID_APS_ROOT ability enabled may join its own thread to partitions. The percentage budgets must not be zero.
SCHED_APS_SEC_FLEXIBLE
Only a process that's running in the System partition with the PROCMGR_AID_APS_ROOT ability enabled can change scheduling parameters. But a process that's running in any partition with the PROCMGR_AID_APS_ROOT ability enabled can create subpartitions, join threads into its own subpartitions, modify subpartitions, and change critical budgets. This lets applications create their own local subpartitions out of their own budgets. The percentage budgets must not be zero.
SCHED_APS_SEC_BASIC
Only a process that's running in the System partition with the PROCMGR_AID_APS_ROOT ability enabled may change overall scheduling parameters. Only a process with the PROCMGR_AID_APS_ROOT ability enabled may set critical budgets.

Unless you're testing the partitioning and want to change all parameters without needing to restart, you should set at least SCHED_APS_SEC_BASIC.

In general, SCHED_APS_SEC_RECOMMENDED is more secure than SCHED_APS_SEC_FLEXIBLE, which is more secure than SCHED_APS_SEC_BASIC. All three allow partitions to be created and modified. After setting up partitions, use SCHED_APS_SEC_PARTITIONS_LOCKED to prevent further unauthorized changes. For example: 

sched_aps_security_parms p; 

APS_INIT_DATA( &p );
p.sec_flags = SCHED_APS_SEC_PARTITIONS_LOCKED;
SchedCtl( SCHED_APS_ADD_SECURITY, &p, sizeof(p));

SCHED_APS_SEC_RECOMMENDED, SCHED_APS_SEC_FLEXIBLE, and SCHED_APS_SEC_BASIC are composed of the flags defined below (but it's usually more convenient for you to use the compound options): 

#define SCHED_APS_SEC_BASIC        (SCHED_APS_SEC_ROOT0_OVERALL | SCHED_APS_SEC_ROOT_MAKES_CRITICAL)

#define SCHED_APS_SEC_FLEXIBLE     (SCHED_APS_SEC_BASIC | SCHED_APS_SEC_NONZERO_BUDGETS |\
                                    SCHED_APS_SEC_ROOT_MAKES_PARTITIONS |\
                                    SCHED_APS_SEC_PARENT_JOINS | SCHED_APS_SEC_PARENT_MODIFIES )

#define SCHED_APS_SEC_RECOMMENDED  (SCHED_APS_SEC_FLEXIBLE | SCHED_APS_SEC_SYS_MAKES_PARTITIONS |\
                                    SCHED_APS_SEC_SYS_JOINS | SCHED_APS_SEC_JOIN_SELF_ONLY)

#define SCHED_APS_SEC_OFF          0x00000000

The individual flags are as follows:

SCHED_APS_SEC_ROOT0_OVERALL
Your process must have the PROCMGR_AID_APS_ROOT ability enabled and be running in the System partition in order to change the overall scheduling parameters, such as the averaging window size.
SCHED_APS_SEC_ROOT_MAKES_PARTITIONS
Your process must have the PROCMGR_AID_APS_ROOT ability enabled in order to create or modify partitions. Applies to the SCHED_APS_CREATE_PARTITION and SCHED_APS_MODIFY_PARTITION commands.
SCHED_APS_SEC_SYS_MAKES_PARTITIONS
You must be running in the System partition in order to create or modify partitions. This applies to same commands as SCHED_APS_SEC_ROOT_MAKES_PARTITIONS.
SCHED_APS_SEC_PARENT_MODIFIES
Allows partitions to be modified (SCHED_APS_MODIFY_PARTITION), but you must be running in the parent partition of the partition being modified. Modify means to change a partition's percentage or critical budget.
SCHED_APS_SEC_NONZERO_BUDGETS
A partition may not be created with, or modified to have, a zero budget. Unless you know that all your partitions need to run only in response to client requests, i.e., receipt of messages, you should set this option.
SCHED_APS_SEC_ROOT_MAKES_CRITICAL
Your process must have the PROCMGR_AID_APS_ROOT ability enabled in order to create a nonzero critical budget or change an existing critical budget.
SCHED_APS_SEC_SYS_MAKES_CRITICAL
You must be running in the System partition to create a nonzero critical budget or change an existing critical budget.
SCHED_APS_SEC_ROOT_JOINS
Your process must have the PROCMGR_AID_APS_ROOT ability enabled in order to join a thread to a partition.
SCHED_APS_SEC_SYS_JOINS
You must be running in the System partition in order to join a thread.
SCHED_APS_SEC_PARENT_JOINS
You must be running in the parent partition of the partition you wish to join to.
SCHED_APS_SEC_JOIN_SELF_ONLY
The caller of the SCHED_APS_JOIN_PARTITION command must specify 0 for the pid and tid. In other words, a process may join only itself to a partition.
SCHED_APS_SEC_PARTITIONS_LOCKED
Prevent further changes to any partition's budget, or overall scheduling parameters, such as the window size. Set this after you've set up your partitions. Once you've locked the partitions, you can still use the SCHED_APS_JOIN_PARTITION command.

Errors:

SchedCtl() and SchedCtl_r() indicate the following errors for the SCHED_APS_ADD_SECURITY command (see the Returns section for details):

EOK
Success.
EACCES
The calling thread doesn't meet the security options set (see SCHED_APS_ADD_SECURITY). Your process must have the PROCMGR_AID_APS_ROOT ability enabled.
EDOM
A reserved field isn't zero. You might not have used APS_INIT_DATA() to initialize the data parameter.
EINVAL
The size of the parameter block doesn't match the size of the expected structure.
ENOSYS
The adaptive partitioning scheduler isn't installed.

SCHED_APS_QUERY_PROCESS

This command returns the partition of the given process. The partition of a process is billed while one of the process's threads handles a pulse. The individual threads in a process may all be in different partitions from the process.

The data argument for this command must be a pointer to a sched_aps_query_process_parms structure: 

typedef struct { 
        int32_t     pid;
        /* out parms: */
        int16_t     id;     /* partition of process */
        int16_t     reserved1;
        int64_t     reserved2;
        int64_t     reserved3;
        int32_t     reserved4;
} sched_aps_query_process_parms;

The members include:

pid
The process ID, or 0 for the calling process.
id
The ID of the process's partition.

Errors:

SchedCtl() and SchedCtl_r() indicate the following errors for the SCHED_APS_QUERY_PROCESS command (see the Returns section for details):

EOK
Success.
EDOM
A reserved field isn't zero. You might not have used APS_INIT_DATA() to initialize the data parameter.
EINVAL
The size of the parameter block doesn't match the size of the expected structure.
ENOSYS
The adaptive partitioning scheduler isn't installed.
ESRCH
The process wasn't found.

SCHED_CONFIGURE (QNX Neutrino 7.0.1 or later)

As a trade-off between latency and throughput, the scheduling algorithm makes decisions that people who expect strict priority scheduling occasionally find surprising:

  • A high-priority thread T that becomes ready on CPU A doesn't always displace a lower-priority thread running on that CPU. Under some circumstances, an interprocessor interruptor (IPI) is sent to CPU B to force it to perform a new scheduling decision, which is expected (but not guaranteed) to cause thread T to run on CPU B.

    Immediately scheduling the higher-priority thread to run on CPU A results in lower thread latency for the high-priority thread, but at the expense of decreased total throughput, as it incurs the cost of interrupting the lower-priority thread and possibly moving it to another CPU.

  • If a thread T that's running on CPU A is displaced by a higher-priority thread, and a thread with a priority lower than T's is running on CPU B, CPU B might not be signalled to reevaluate its scheduling decision. High-priority threads normally perform small amounts of work and then voluntarily suspend themselves. In that case, migrating thread T is likely unnecessary and would reduce the total system throughput.

The end result is that only the highest-priority thread in the system is guaranteed to run on some CPU, while the other CPUs may be running threads with lower priorities than those ready to run at any given point in time. The SCHED_CONFIGURE command provides some parameters that you can use to tune the scheduler.

Note:
In order to use this command, your process must have the PROCMGR_AID_SCHEDULE ability enabled; see procmgr_ability().

The data argument for this command must be a pointer to a struct sched_config. This structure includes the following members:

int32_t low_latency_priority
The priority threshold above which a thread always displaces a lower-priority thread running on the CPU on which it becomes ready. Effectively, this parameter lets you define a priority class as low latency, avoiding the overhead of an IPI and a new scheduling decision by another CPU.
int32_t migrate_priority
The priority threshold above which a preempted thread will be rescheduled on another CPU (the one running the lowest-priority thread).

Keeping both parameters at their default values (INT_MAX) maintains the scheduling behavior described above.

For example, suppose there are three threads, T20, T10, and T5, where the priority of each thread matches the thread's label, and that T10 is running on CPU A, and T5 is running on CPU B. If thread T20 becomes ready on CPU A, then the results are as follows:

  • If low_latency_priority > 20, T20 migrates to CPU B and displaces T5, leaving T10 and T20 running, but the thread latency of T20 was impacted by the necessity of sending an IPI to CPU B to perform the rescheduling there.
  • If low_latency_priority <= 20, T20 preempts T10 immediately and thus minimizes its thread latency, but at the expense of migrating T10 to another CPU.
  • If T10 is preempted, then:
    • If migrate_priority > 10, T10 doesn't migrate and doesn't run, leaving T5 running while T10 is ready.
    • If migrate_priority <= 10, T10 migrates to CPU B and displaces T5.

Errors:

SchedCtl() and SchedCtl_r() indicate the following errors for the SCHED_CONFIGURE command (see the Returns section for details):

EOK
Success.
EINVAL
The size of the parameter block doesn't match the size of the expected structure.
EPERM
You don't have the PROCMGR_AID_SCHEDULE ability enabled.

SCHED_CONT_APP and SCHED_STOP_APP (QNX Neutrino 7.0 or later)

The SCHED_STOP_APP and SCHED_CONT_APP commands make all processes with the given application ID stop or continue. Stop means that no thread in any of these processes is scheduled, and continue means allowing these threads to be scheduled again, subject to their current state. You use these commands like this (for more information, see "Application groups" in the QNX Neutrino System Security Guide): 

if ( SchedCtl( SCHED_STOP_APP, (void *)appid, 0) == -1 ) {
   /* An error occurred */
}

...

if ( SchedCtl( SCHED_CONT_APP, (void *)appid, 0) == -1 ) {
   /* An error occurred */
}

This mechanism is independent of the SIGSTOP and SIGCONT signals; for example, a SIGCONT doesn't resume a thread that belongs to a process that was stopped by a SchedCtl(SCHED_STOP_APP, ...) call. Nevertheless, in order to successfully issue these commands, your process must have the PROCMGR_AID_SIGNAL ability enabled such that you could send the appropriate signal:

  • SIGCONT for SCHED_CONT_APP
  • SIGSTOP for SCHED_STOP_APP

For more information about PROCMGR_AID_SIGNAL, see procmgr_ability().

This mechanism interacts with the _NTO_TCTL_ONE_THREAD_CONT and _NTO_TCTL_ONE_THREAD_HOLD commands for ThreadCtl() as follows:

  • SCHED_STOP_APP stops threads in the specified application that are running.
  • SCHED_CONT_APP starts threads in the specified application that were stopped by SCHED_STOP_APP, but not those that were stopped by _NTO_TCTL_ONE_THREAD_HOLD.
  • _NTO_TCTL_ONE_THREAD_CONT starts threads that were stopped by _NTO_TCTL_ONE_THREAD_HOLD or SCHED_STOP_APP.

Errors:

SchedCtl() and SchedCtl_r() indicate the following errors for the SCHED_CONT_APP and SCHED_STOP_APP commands (see the Returns section for details):

EOK
Success; at least one app was made to continue or stop, depending on the command.
EPERM
You don't have the PROCMGR_AID_SIGNAL ability enabled for the appropriate signal.
ESRCH
No process with the given application ID was found, or the application ID is the one for the process manager. For more information, see "Application groups" in the QNX Neutrino System Security Guide.

Blocking states

These calls don't block.

Returns:

The only difference between these functions is the way they indicate errors:

SchedCtl()
0 if the call succeeds. If an error occurs, SchedCtl() returns -1 and sets errno.
SchedCtl_r()
EOK is returned on success. This function does NOT set errno. If an error occurs, any of the error codes listed in the command descriptions above may be returned.

Examples:

sched_aps_partition_info part_info; 

// You need to initialize the parameter block.
APS_INIT_DATA(&part_info); 

// Set the input members of the parameter block.
part_info.id = 2;

// Invoke SchedCtl to query the partition. 
ret = SchedCtl( SCHED_APS_QUERY_PARTITION, &part_info,
      sizeof(part_info) );
if (EOK!=ret) some_kind_of_error_handler(); 

// Use output field 
printf( "The budget is %d per cent.\n",
        part_info.budget_percent);

Classification:

QNX Neutrino

Safety:
Cancellation point No
Interrupt handler No
Signal handler Yes
Thread Yes
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