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sched_setparam - set scheduling parameters (REALTIME)
#include <sched.h>
int sched_setparam(pid_t pid, const struct sched_param
*param);
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 the appropriate privilege to set its own scheduling parameters or those of another process.
The target process, whether it is running or not running, shall be moved to the tail of the thread list for its priority.
If the priority of the process specified by the pid argument is set higher than that of the lowest priority running process and if the specified process is ready to run, the process specified by the pid argument shall preempt a lowest priority running process. Similarly, if the process calling sched_setparam() sets its own priority lower than that of one or more other non-empty process lists, then the process that is the head of the highest priority list shall also preempt the calling process. Thus, in either case, the originating process might not receive notification of the completion of the requested priority change until the higher priority process has executed.
If the scheduling policy of the target process is SCHED_SPORADIC, the value specified by the sched_ss_low_priority member of the param argument shall be any integer within the inclusive priority range for the sporadic server policy. The sched_ss_repl_period and sched_ss_init_budget members of the param argument shall represent the time parameters to be used by the sporadic server scheduling policy for the target process. The sched_ss_max_repl member of the param argument shall represent the maximum number of replenishments that are allowed to be pending simultaneously for the process scheduled under this scheduling policy.
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.
If the scheduling policy of the target process is either SCHED_FIFO or SCHED_RR, the sched_ss_low_priority, sched_ss_repl_period, and sched_ss_init_budget members of the param argument shall have no effect on the scheduling behavior. If the scheduling policy of this process is not SCHED_FIFO, SCHED_RR, or SCHED_SPORADIC, the effects of these members are implementation-defined; this case includes the SCHED_OTHER policy.
If the current scheduling policy for the process specified by pid is not SCHED_FIFO, SCHED_RR, or SCHED_SPORADIC, the result is implementation-defined; this case includes the SCHED_OTHER policy.
The effect of this function on individual threads is dependent on the scheduling contention scope of the threads:
For threads with system scheduling contention scope, these functions shall have no effect on their scheduling.
For threads with process scheduling contention scope, the threads' scheduling parameters shall not be affected. However, the scheduling of these threads with respect to threads in other processes may be dependent on the scheduling parameters of their process, which are governed using these functions.
If an implementation supports a two-level scheduling model in which library threads are multiplexed on top of several kernel-scheduled entities, then the underlying kernel-scheduled entities for the system contention scope threads shall not be affected by these functions.
The underlying kernel-scheduled entities for the process contention scope threads shall have their scheduling parameters changed to the value specified in param. Kernel-scheduled entities for use by process contention scope threads that are created after this call completes shall inherit their scheduling policy and associated scheduling parameters from the process.
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.
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.
The sched_setparam() function shall fail if:
The following sections are informative.
sched_getparam() , sched_getscheduler() , sched_setscheduler() , the Base Definitions volume of IEEE Std 1003.1-2001, <sched.h>
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