sched_param

Description:

You'll use the sched_param structure when you get or set the scheduling parameters for a thread or process.

You can use these functions to get the scheduling parameters:

• pthread_attr_getschedparam()
• pthread_getschedparam()
• sched_getparam()
• SchedGet()

You can use these functions to set the scheduling parameters:

• pthread_attr_setschedparam()
• pthread_setschedparam()
• pthread_setschedprio()
• sched_setparam()
• sched_setscheduler()
• SchedSet()
• ThreadCreate()

The members of sched_param include:

sched_priority

When you get the scheduling parameters, this member reflects the priority that was assigned to the thread or process. It doesn't reflect any temporary adjustments due to priority inheritance.

When you set the scheduling parameters, set this member to the priority that you want to use. The priority must be between the minimum and maximum values returned by sched_get_priority_min() and sched_get_priority_max() for the scheduling policy.

As an extension to POSIX in QNX Neutrino 6.6 or later, you can wrap the new priority in one these macros to specify how to handle out-of-range priority requests:

• SCHED_PRIO_LIMIT_ERROR(priority) — indicate an error
• SCHED_PRIO_LIMIT_SATURATE(priority) — use the maximum allowed priority (reach a “maximum saturation point”)

If procnto was started with a -P option ending with s or S, out-of-range priority requests by default “saturate” at the maximum allowed value.

Note: In order to create a thread whose priority is above the maximum permitted for unprivileged processes, your process must have the PROCMGR_AID_PRIORITY ability enabled. For more information, see procmgr_ability().

sched_curpriority

When you get the scheduling parameters, this member is set to the priority that the thread or process is currently running at. This is the value that the kernel uses when making scheduling decisions.

When you set the scheduling parameters, this member is ignored.

The other members are used with sporadic scheduling. The following #define directives create the POSIX names that correspond to those members and should be used instead of accessing members directly.

sched_ss_low_priority

The background or low priority for the thread that's executing.

sched_ss_max_repl

The maximum number of times a replenishment will be scheduled, typically because of a blocking operation. After a thread has blocked this many times, it automatically drops to the low-priority level for the remainder of its execution until its execution budget is replenished.

sched_ss_repl_period

The time that should be used for scheduling the replenishment of an execution budget after being blocked or having overrun the maximum number of replenishments. This time is used as an offset against the time that a thread is made READY.

sched_ss_init_budget

The time that should be used for the thread's execution budget. As the thread runs at its high-priority level, its execution time is carved out of this budget. Once the budget is entirely depleted, the thread drops to its low-priority level, where, if possible because of priority arrangements, it can continue to run until the execution budget is replenished.

For more information, see “Scheduling policies” in the QNX Neutrino Microkernel chapter of the System Architecture guide.

Examples:

This code shows a duty-cycle usage of the sporadic server thread:

#include <stdio.h>
#include <errno.h>
#include <sched.h>
#include <pthread.h>
#include <inttypes.h>
#include <sys/syspage.h>
#include <sys/neutrino.h>

/* 50 % duty cycle of 5 secs on 5 secs off */
struct timespec g_init_budget = { 5, 0 };
struct timespec g_repl_period = { 10, 0 };

#define MY_HIGH_PRIORITY 5
#define MY_LOW_PRIORITY 4
#define MY_REPL_PERIOD g_repl_period
#define MY_INIT_BUDGET g_init_budget
#define MY_MAX_REPL 10

#define DUTY_CYCLE_LOOPS 10

/*
 Run a compute-bound thread (minimal blocking) to show the
 duty cycle.
*/
void *st_duty_check(void *arg) {
    struct sched_param  params;
    uint64_t        stime, etime, cps;
    double          secs;
    int         ret, prio;
    int         prevprio, iterations;

    stime = ClockCycles();
    cps = SYSPAGE_ENTRY(qtime)->cycles_per_sec;
    iterations = 0;

    printf("\n");

    prevprio = -1;
    while(iterations < DUTY_CYCLE_LOOPS) {
        etime = ClockCycles();
        ret = pthread_getschedparam(pthread_self(), &prio,
                                    &params);

        if(ret != 0) {
            printf("pthread_getschedparam() failed %d \n",
                   errno);
            break;
        } else if (prevprio != -1 && prevprio !=
                   params.sched_priority) {
            stime = etime - stime;
            secs = (double)stime / (double)cps;
            printf("pri %d (cur %d) %lld cycles %g secs\n", 
                params.sched_priority, 
                params.sched_curpriority, 
                stime, secs);
            stime = etime;
            iterations++;
        }
        prevprio = params.sched_priority;
    }

    return NULL;
}

int main(int argc, char **argv) {
    struct sched_param params;
    pthread_attr_t     attr;
    pthread_t      thr;
    int        ret;

    /* Set the attribute structure with the sporadic values */
    printf("# Set sporadic attributes ...");
    pthread_attr_init(&attr);
    ret = pthread_attr_setinheritsched(&attr,
             PTHREAD_EXPLICIT_SCHED);
    if(ret != 0) {
        printf("pthread_attr_setinheritsched() failed %d \n",
               errno);
        return 1;
    }

    ret = pthread_attr_setschedpolicy(&attr, SCHED_SPORADIC);
    if(ret != 0) {
        printf("pthread_attr_setschedpolicy() failed %d %d\n",
               ret, errno);
        return 1;
    } 

    params.sched_priority = MY_HIGH_PRIORITY;
    params.sched_ss_low_priority = MY_LOW_PRIORITY;
    memcpy(&params.sched_ss_init_budget, &MY_INIT_BUDGET,
           sizeof(MY_INIT_BUDGET));
    memcpy(&params.sched_ss_repl_period, &MY_REPL_PERIOD,
           sizeof(MY_REPL_PERIOD));
    params.sched_ss_max_repl = MY_MAX_REPL; 
    ret = pthread_attr_setschedparam(&attr, &params);
    if(ret != 0) {
        printf("pthread_attr_setschedparam() failed %d \n", errno);
        return 1;
    }
    printf("OK\n");

    /* Create a sporadic thread to check the duty cycle */
    printf("# Creating thread duty cycle thread (%d changes) ... ",
           DUTY_CYCLE_LOOPS);
    ret = pthread_create(&thr, &attr, st_duty_check, NULL);
    if(ret != 0) {
        printf("pthread_create() failed %d \n", errno);
        return 1;
    }
    pthread_join(thr, NULL);
    printf("OK\n");

    return 0;
}

See also sched_getparam().

Classification:

POSIX 1003.1 PS