SCHED_SETSCHEDULER(P) POSIX Programmer's Manual SCHED_SETSCHEDULER(P)NAMEsched_setscheduler - set scheduling policy and parameters (REALTIME)
SYNOPSIS
#include <sched.h>
int sched_setscheduler(pid_t pid, int policy,
const struct sched_param *param);
DESCRIPTION
The sched_setscheduler() function shall set the scheduling policy and
scheduling parameters of the process specified by pid to policy and the
parameters specified in the sched_param structure pointed to by param,
respectively. The value of the sched_priority member in the sched_param
structure shall be any integer within the inclusive priority range for
the scheduling policy specified by policy. If the value of pid is neg‐
ative, the behavior of the sched_setscheduler() function is unspeci‐
fied.
The possible values for the policy parameter are defined in the
<sched.h> header.
If a process specified by pid exists, and if the calling process has
permission, the scheduling policy and scheduling parameters shall be
set for the process whose process ID is equal to pid.
If pid is zero, the scheduling policy and scheduling parameters shall
be set for the calling process.
The conditions under which one process has the appropriate privilege to
change the scheduling parameters of another process are implementation-
defined.
Implementations may require that the requesting process have permission
to set its own scheduling parameters or those of another process. Addi‐
tionally, implementation-defined restrictions may apply as to the
appropriate privileges required to set a process' own scheduling pol‐
icy, or another process' scheduling policy, to a particular value.
The sched_setscheduler() function shall be considered successful if it
succeeds in setting the scheduling policy and scheduling parameters of
the process specified by pid to the values specified by policy and the
structure pointed to by param, respectively.
If the scheduling policy specified by policy is SCHED_SPORADIC, the
value specified by the sched_ss_low_priority member of the param argu‐
ment shall be any integer within the inclusive priority range for the
sporadic server policy. The sched_ss_repl_period and sched_ss_init_bud‐
get members of the param argument shall represent the time parameters
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 simul‐
taneously 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 specified by policy 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.
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 policy and associated 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 policy and associated sched‐
uling parameters changed to the values specified in policy and param,
respectively. 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 and associated sched‐
uling parameters for the underlying kernel-scheduled entities used by
the process contention scope threads.
RETURN VALUE
Upon successful completion, the function shall return the former sched‐
uling policy of the specified process. If the sched_setscheduler()
function fails to complete successfully, the policy and scheduling
parameters shall remain unchanged, and the function shall return a
value of -1 and set errno to indicate the error.
ERRORS
The sched_setscheduler() function shall fail if:
EINVAL The value of the policy parameter is invalid, or one or more of
the parameters contained in param is outside the valid range for
the specified scheduling policy.
EPERM The requesting process does not have permission to set either or
both of the scheduling parameters or the scheduling policy of
the specified process.
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 ALSOsched_getparam() , sched_getscheduler() , sched_setparam() , 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 .
IEEE/The Open Group 2003 SCHED_SETSCHEDULER(P)
