NAME

sched_setparam — set scheduling parameters (REALTIME)

SYNOPSIS

[PS] #include <sched.h>

int sched_setparam(pid_t pid, const struct sched_param *param);

DESCRIPTION

The sched_setparam() function shall set the scheduling parameters of the process specified by pid to the values specified by the sched_param structure pointed to by param. The value of the sched_priority member in the sched_param structure shall be any integer within the inclusive priority range for the current scheduling policy of the process specified by pid. Higher numerical values for the priority represent higher priorities. If the value of pid is negative, the behavior of the sched_setparam() function is unspecified.

If a process specified by pid exists, and if the calling process has permission, the scheduling parameters shall be set for the process whose process ID is equal to pid.

If pid is zero, the scheduling parameters shall be set for the calling process.

The conditions under which one process has permission to change the scheduling parameters of another process are implementation-defined.

Implementations may require the requesting process to have appropriate privileges to set its own scheduling parameters or those of another process.

See Scheduling Policies for a description on how this function affects the scheduling of the threads within the target process.

If the current scheduling policy for the target process is not SCHED_FIFO, SCHED_RR, ^[SS] or SCHED_SPORADIC,  the result is implementation-defined; this case includes the SCHED_OTHER policy.

^[SS] The specified sched_ss_repl_period shall be greater than or equal to the specified sched_ss_init_budget for the function to succeed; if it is not, then the function shall fail.

The value of sched_ss_max_repl shall be within the inclusive range [1,{SS_REPL_MAX}] for the function to succeed; if not, the function shall fail. It is unspecified whether the sched_ss_repl_period and sched_ss_init_budget values are stored as provided by this function or are rounded to align with the resolution of the clock being used.

This function is not atomic with respect to other threads in the process. Threads may continue to execute while this function call is in the process of changing the scheduling policy for the underlying kernel-scheduled entities used by the process contention scope threads.

RETURN VALUE

If successful, the sched_setparam() function shall return zero.

If the call to sched_setparam() is unsuccessful, the priority shall remain unchanged, and the function shall return a value of -1 and set errno to indicate the error.

ERRORS

The sched_setparam() function shall fail if:

[EINVAL]

One or more of the requested scheduling parameters is outside the range defined for the scheduling policy of the specified pid.

[EPERM]

The requesting process does not have permission to set the scheduling parameters for the specified process, or does not have appropriate privileges to invoke sched_setparam().

[ESRCH]

No process can be found corresponding to that specified by pid.

EXAMPLES

None.

APPLICATION USAGE

None.

RATIONALE

None.

FUTURE DIRECTIONS

None.

SEE ALSO

Scheduling Policies, sched_getparam, sched_getscheduler, sched_setscheduler

XBD <sched.h>

CHANGE HISTORY

First released in Issue 5. Included for alignment with the POSIX Realtime Extension.

Issue 6

The sched_setparam() function is marked as part of the Process Scheduling option.

The [ENOSYS] error condition has been removed as stubs need not be provided if an implementation does not support the Process Scheduling option.

The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:

• In the DESCRIPTION, the effect of this function on a thread's scheduling parameters is added.

• Sections describing two-level scheduling and atomicity of the function are added.

The SCHED_SPORADIC scheduling policy is added for alignment with IEEE Std 1003.1d-1999.

IEEE PASC Interpretation 1003.1 #100 is applied.

Issue 7

Austin Group Interpretation 1003.1-2001 #061 is applied, updating the DESCRIPTION.

Austin Group Interpretation 1003.1-2001 #119 is applied, clarifying the accuracy requirements for the sched_ss_repl_period and sched_ss_init_budget values.