qos_latency.c

#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <unistd.h>
#include <signal.h>
#include <string.h>
#include <errno.h>

#define QOS_DEV "/dev/system_wakeup_latency"

static int fd = -1;
static volatile int keep_running = 1;

void signal_handler(int sig) {
    printf("\nCaught signal %d, cleaning up and exiting...\n", sig);
    keep_running = 0;
}

void setup_signal_handlers(void) {
    struct sigaction sa;

    memset(&sa, 0, sizeof(sa));
    sa.sa_handler = signal_handler;
    sigaction(SIGINT, &sa, NULL);
    sigaction(SIGTERM, &sa, NULL);
}

int main(int argc, char *argv[]) {
    int latency_us;
    char buffer[32];

    if (argc != 2) {
        fprintf(stderr, "Usage: %s <latency_in_us>\n", argv[0]);
        return 1;
    }

    latency_us = atoi(argv[1]);
    if (latency_us < 0) {
        fprintf(stderr, "Error: Latency value must be non-negative\n");
        return 1;
    }

    printf("Setting system wakeup latency QoS to %d us\n", latency_us);

    /* Open the QoS file */
    fd = open(QOS_DEV, O_RDWR);
    if (fd < 0) {
        fprintf(stderr, "Error opening %s: %s\n", QOS_DEV, strerror(errno));
        return 1;
    }

    /* Write the latency value */
    snprintf(buffer, sizeof(buffer), "%d", latency_us);
    if (write(fd, buffer, strlen(buffer)) < 0) {
        fprintf(stderr, "Error writing to %s: %s\n", QOS_DEV, strerror(errno));
        close(fd);
        return 1;
    }

    setup_signal_handlers();

    printf("QoS constraint set successfully. Process will keep running to maintain the constraint.\n");
    printf("Press Ctrl+C to exit and release the constraint.\n");

    /* Keep the program running to maintain the file descriptor open */
    while (keep_running) {
        sleep(1);
    }

    /* Close the file descriptor before exiting */
    if (fd >= 0) {
        close(fd);
    }

    printf("QoS constraint released.\n");

    return 0;
}

qos_wake_latency.c

#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <signal.h>

#define QOS_DEV "/dev/system_wakeup_latency"
#define LATENCY_VAL "0x64"  /* 100 us in hex */

static volatile int keep_running = 1;

void sig_handler(int sig) {
    keep_running = 0;
}

int main(void) {
    int fd;

    signal(SIGINT, sig_handler);
    signal(SIGTERM, sig_handler);

    fd = open(QOS_DEV, O_RDWR);
    if (fd < 0) {
        perror("open");
        return 1;
    }

    if (write(fd, LATENCY_VAL, sizeof(LATENCY_VAL) - 1) < 0) {
        perror("write");
        close(fd);
        return 1;
    }

    printf("QoS set to %s. Press Ctrl+C to exit.\n", LATENCY_VAL);

    while (keep_running)
        sleep(1);

    close(fd);
    printf("Released.\n");
    return 0;
}