Use FIFO scheduling policy and Core affinity in linux

SHED_FIFO.c

#define _GNU_SOURCE

#include <pthread.h>
#include <stdlib.h>
#include <stdio.h>
#include <sched.h>
#include <sys/sysinfo.h>
#include <sys/types.h>
#include <unistd.h>
#include <syslog.h>

#define NUM_OF_THREADS  128
#define SCHED_POLICY SCHED_FIFO

typedef struct
{
    int threadIdx;
} threadParams_t;

struct sched_param fifo_param;

pthread_attr_t fifo_sched_attr;

// POSIX thread declarations and scheduling attributes
//
pthread_t threads[NUM_OF_THREADS];
threadParams_t threadParams[NUM_OF_THREADS];

void print_scheduler(void)
{
  int schedType = sched_getscheduler(getpid());

  switch(schedType)
  {
    case SCHED_FIFO:
      printf("SCHED_FIFO\n");
      break;
    case SCHED_OTHER:
      printf("SCHED_OTHER\n");
      break;
    case SCHED_RR:
      printf("SCHED_RR\n");
      break;
    default:
      printf("UNKNOWN\n");
  }
}



void set_scheduler(int procno, int prio)
{
  int scope, rc, cpuidx;
  cpu_set_t cpuset;

  printf("INITIAL "); print_scheduler();

  //SCHED_POLICY is set to SCHED_FIFO
  pthread_attr_init(&fifo_sched_attr);
  pthread_attr_setinheritsched(&fifo_sched_attr, PTHREAD_EXPLICIT_SCHED);
  pthread_attr_setschedpolicy(&fifo_sched_attr, SCHED_POLICY);

  //zero out the set o CPU cores
  CPU_ZERO(&cpuset);
  
  //Here we assign the threads to run ONLY on single core
  cpuidx=procno;
  CPU_SET(cpuidx, &cpuset);
  pthread_attr_setaffinity_np(&fifo_sched_attr, sizeof(cpu_set_t), &cpuset);

  //Set priority according to function parameter
  fifo_param.sched_priority=prio;

  if ((rc=sched_setscheduler(getpid(), SCHED_POLICY, &fifo_param)) < 0)
    perror("sched_setscheduler");

  pthread_attr_setschedparam(&fifo_sched_attr, &fifo_param);

  printf("ADJUSTED "); print_scheduler();


}

void *Thread(void *threadp)
{
    threadParams_t *threadParams = (threadParams_t *)threadp;
    int gsum = 0;			//Local variable (for every task)
    char str[100];			//Memory allocation for string

    for(int i=0; i<=threadParams->threadIdx; i++)	//Calculate sum from 0 to the n, where n is the task number
      gsum=gsum+i;
    sprintf(str, "Thread idx=%d, sum[1..%d]=%d Running on core:%d\n", threadParams->threadIdx, threadParams->threadIdx, gsum, sched_getcpu()); //Fill the string with calculated data
    syslog(LOG_INFO, str);		//Log the data
}



int main (int argc, char *argv[])
{
   volatile int i=0;

   openlog("[COURSE:1][ASSIGNMENT:3]:", LOG_NOWAIT, LOG_SYSLOG);    //Open logger file
   system("uname -a | logger -t '[COURSE:1][ASSIGNMENT:3]:'");      //Use system function for OS details and stream it to logger

   for(i=0; i < NUM_OF_THREADS; i++)
   {
     set_scheduler(1, 99-i);		//Set scheduler to FIFO runing on core 1 with priority from 99 to 0
     threadParams[i].threadIdx=i;	//Set thread identification number
     pthread_create(&threads[i],   	//Pointer to thread descriptor
                  &fifo_sched_attr,     //Use default attributes
                  Thread, 		//Thread function entry point
                  (void *)&(threadParams[i]) //Parameters to pass in
                 );
   }

   for(i=0; i < NUM_OF_THREADS; i++)
     pthread_join(threads[i], NULL);

   printf("TEST COMPLETE\n");
}



/* --=== COMMENTS ON THE OUTPUT DATA ===--
 *
 * Below please find few lines from the syslog file
 * gru 11 12:35:21 diodetetor [COURSE:1][ASSIGNMENT:3]:[173145]: Linux diodetetor 5.15.5-arch1-1 #1 SMP PREEMPT Thu, 25 Nov 2021 22:09:33 +0000 x86_64 GNU/Linux
 * gru 11 12:35:21 diodetetor [COURSE:1][ASSIGNMENT:3]:[173142]: Thread idx=0, sum[1..0]=0 Running on core:1
 * gru 11 12:35:21 diodetetor [COURSE:1][ASSIGNMENT:3]:[173142]: Thread idx=1, sum[1..1]=1 Running on core:1
 * gru 11 12:35:21 diodetetor [COURSE:1][ASSIGNMENT:3]:[173142]: Thread idx=2, sum[1..2]=3 Running on core:1
 * gru 11 12:35:21 diodetetor [COURSE:1][ASSIGNMENT:3]:[173142]: Thread idx=3, sum[1..3]=6 Running on core:1
 * gru 11 12:35:21 diodetetor [COURSE:1][ASSIGNMENT:3]:[173142]: Thread idx=4, sum[1..4]=10 Running on core:1
 * gru 11 12:35:21 diodetetor [COURSE:1][ASSIGNMENT:3]:[173142]: Thread idx=5, sum[1..5]=15 Running on core:1
 * gru 11 12:35:21 diodetetor [COURSE:1][ASSIGNMENT:3]:[173142]: Thread idx=6, sum[1..6]=21 Running on core:1
 * gru 11 12:35:21 diodetetor [COURSE:1][ASSIGNMENT:3]:[173142]: Thread idx=7, sum[1..7]=28 Running on core:1
 * gru 11 12:35:21 diodetetor [COURSE:1][ASSIGNMENT:3]:[173142]: Thread idx=8, sum[1..8]=36 Running on core:1
 * gru 11 12:35:21 diodetetor [COURSE:1][ASSIGNMENT:3]:[173142]: Thread idx=9, sum[1..9]=45 Running on core:1
 * gru 11 12:35:21 diodetetor [COURSE:1][ASSIGNMENT:3]:[173142]: Thread idx=10, sum[1..10]=55 Running on core:1
 * gru 11 12:35:21 diodetetor [COURSE:1][ASSIGNMENT:3]:[173142]: Thread idx=11, sum[1..11]=66 Running on core:1
 * gru 11 12:35:21 diodetetor [COURSE:1][ASSIGNMENT:3]:[173142]: Thread idx=12, sum[1..12]=78 Running on core:1
 * gru 11 12:35:21 diodetetor [COURSE:1][ASSIGNMENT:3]:[173142]: Thread idx=13, sum[1..13]=91 Running on core:1
 *
 *  As we can see, the tasks are in the same order as the creation sequence. This is because
 *  of assymetric fifo schedduler SCHED_FIFO and proper priority settings.