Process scheduling in POSIX

Process Schudling

POSIX, processes run with a particular scheduling policy and associated scheduling attributes. Both the policy and the attributes can be changed independently. POSIX defines three policies: 1. SCHED_FIFO : Preemptive, priority-based scheduling.untill process not blocked. 2. SCHED_RR : Preemptive, priority-based scheduling with quanta. 3. SCHED_OTHER : An implementation-defined scheduler. Header file #include <sched.h> macro should defined _POSIX_PRIORITY_SCHEDULING

Process scheduling APIs

sched_getscheduler—Retrieve scheduling algorithm for a particular purpose. int sched_getscheduler(pid_t pid); if pid=0 then return scheduler of calling process. sched_setscheduler—Set scheduling algorithm/parameters for a process. int sched_setscheduler(pid_t pid, int policy, const struct sched_param *p); sched_get_priority_max—Get maximum priority value for a scheduler. int sched_get_priority_max(int alg); sched_get_priority_min — Get minimum priority value for a scheduler. int sched_get_priority_min(int alg); sched_getparam—Retrieve scheduling parameters for a particular process. int sched_getparam(pid_t pid, struct sched_param *p); sched_setparam — Set scheduling parameters for a process. int sched_setparam(pid_t pid, const struct sched_param *p); sched_yield — Yield the processor.sched_yield, when called, causes the calling process to give up its processor, and move to the back of the queue for its priority. int sched_yield(); sched_rr_get_interval—Get the SCHED_RR interval for the named process. int sched_rr_get_interval(pid_t pid, struct timespec *t);