NAME
sched_setparam - set scheduling parameters (REALTIME)
SYNOPSIS
#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 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.
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 the appropriate privilege to invoke sched_setparam().
ESRCH No process can be found corresponding to that specified by pid.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
None.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
sched_getparam() , sched_getscheduler() , sched_setscheduler() , the
Base Definitions volume of IEEE Std 1003.1-2001, <sched.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.opengroup.org/unix/online.html .