dma_latency.c

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

static int pm_qos_fd = -1;

static void start_low_latency(void) {
	int32_t target = 0;

	if (pm_qos_fd >= 0) {
		return;
	}

	pm_qos_fd = open("/dev/cpu_dma_latency", O_RDWR);
	if (pm_qos_fd < 0) {
		fprintf(stderr, "Failed to open PM QOS file: %s",
				strerror(errno));
		exit(errno);
	}
	write(pm_qos_fd, &target, sizeof(target));
}

static void stop_low_latency(void) {
	if (pm_qos_fd >= 0)
		close(pm_qos_fd);
}

int main (int argc, char **argv) {
	start_low_latency();
	while (1) {
		sleep (1);
	}
	stop_low_latency();
	return 0;
}