/*
 * License: GPL v2 [GNU Public License v2]
 * original: sched_jitter.c
 *   15-Jan-2004 posted to LKML by Der Herr Hofrat (der.herr@hofr.at)
 *   14-Apr-2005 modified and changed name to sched2.c by Atomu Hidaka (hidaka@devdrv.com)
 */
#include <stdio.h>
#include <stdlib.h>
#include <sched.h>
#include <string.h>
#include <limits.h>
#include <unistd.h>
#include <fcntl.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <sys/io.h>
#include <sys/wait.h>

void usage(void);
char *myname;

__inline__ unsigned long long int hwtime(void)
{
	unsigned long long int x;
	__asm__ __volatile__("rdtsc\n\t"
		:"=A" (x));
	return x;
}

void usage(void)
{
   printf("usage: %s -s tsc_scaler\n", myname);
}

void co_process(void)
{
	/* always SCHED_RR process */
	struct sched_param param;
	param.sched_priority = sched_get_priority_max(SCHED_RR);
	if(sched_setscheduler(getpid(),SCHED_RR,&param)){
		printf("sched_setscheduler failed - exiting\n");
		exit(-1);
	} 

	while(1) {
		usleep(500);
	}
}

#define GRAPH_SIZE 500

int main(int argc, char **argv)
{
	int i;
	char  *optstr = "hs:";
	char c;
	unsigned long long graph[3][GRAPH_SIZE+1];
	unsigned long long hwtime1,hwtime2,jitt;
	unsigned long long jitt_max[3];
	unsigned long scale = 1;
	unsigned long policy;
	unsigned long long n,loops;
	struct sched_param param;
	pid_t cpid;

	myname = argv[0];
	while ( (c = getopt(argc, argv, optstr)) != -1 ) {
		switch (c) {
		case 's':   /* tsc scaling factor */
			scale = strtol( optarg, NULL, 0);
			break;
		case 'h':   /* verbose */
			usage();
			exit(0);
		default:
			fprintf(stderr,"time: Unknown option \'-%c\', exitting.\n", c);
			fprintf(stderr,"   use \'time -h\' for help\n");
			exit(1);
		}
	}

	cpid = fork();
	if (!cpid) { /* child */
		co_process();
		exit(0);
	}

	/* from linux/include/sched.h 
	 * #define SCHED_NORMAL            0
	 * #define SCHED_FIFO              1
	 * #define SCHED_RR                2
	 */
	memset(graph,0,sizeof(graph));

	/* just run with SCHED_FIFO and then SCHED_RR */
	for(policy=0;policy<3;policy++){
		//nice(-20);
		param.sched_priority = sched_get_priority_max(policy);
//		param.sched_priority = sched_get_priority_min(policy);
		if(sched_setscheduler(getpid(),policy,&param)){
			printf("sched_setscheduler failed - exiting\n");
			exit(-1);
		} 
		jitt_max[policy]=0LL; 
		n=0LL;
		loops=1000000000LL;
////		loops= 200000000LL; // for debug
		while(n < loops){
			unsigned long long index=0;

			hwtime2 = hwtime();
			hwtime1 = hwtime();
			jitt=hwtime1-hwtime2;
			index=jitt/scale;
			if(index >= GRAPH_SIZE){
				graph[policy][GRAPH_SIZE] += 1;
			} else {
				graph[policy][index] += 1;
			}
			if(jitt > jitt_max[policy]){
				jitt_max[policy]=jitt;
			}
			n++;
		}
	}
	kill(cpid, SIGKILL);
	wait(NULL);

	/* dump data */
	for(policy=0;policy<3;policy++){
		if(jitt_max[policy]/scale < GRAPH_SIZE){
			printf("\nworst case delay in run with policy %ld = %lld us\n",
				policy,
				jitt_max[policy]/scale);
		} else {		
			printf("\nworst case delay in run with policy %ld = %lld us out of bounds - results are unreliable !\n",
				policy,
				jitt_max[policy]/scale);
		}
		printf("\n");
		for(i=0;i<GRAPH_SIZE ;i++){
			if(graph[policy][i])
				printf("%4d us: %16lld \n",i,graph[policy][i]);
		}
		if(jitt_max[policy]/scale >= GRAPH_SIZE){
				printf("OutBnd.: %16lld \n",graph[policy][GRAPH_SIZE]);
		}
	}
	return 0;
}