Chapter 31. Displaying the priority for a process

Procedure

1. Create the get_sched.c source file and open it in a text editor.

   $ {EDITOR} get_sched.c

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2. Add the following lines into the file.

   #include <sched.h>
   #include <unistd.h>
   #include <stdio.h>
   
   int main()
   {
     int policy;
     pid_t pid = getpid();
   
     policy = sched_getscheduler(pid);
     printf("Policy for pid %ld is %i.\n", (long) pid, policy);
     return 0;
   }

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   The policy variable holds the scheduler policy for the specified process.

3. Compile the program.

   $ gcc get_sched.c -o get_sched

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4. Run the program with varying policies.

   $ chrt -o 0 ./get_sched
   Policy for pid 27240 is 0.
   $ chrt -r 10 ./get_sched
   Policy for pid 27243 is 2.
   $ chrt -f 10 ./get_sched
   Policy for pid 27245 is 1.

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Procedure

1. Create the sched_get.c source file and open it in a text editor.

   $ {EDITOR} sched_get.c

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2. Enter the following into the file:

   #include <stdio.h>
   #include <unistd.h>
   #include <sched.h>
   
   int main()
   {
   
     printf("Valid priority range for SCHED_OTHER: %d - %d\n",
            sched_get_priority_min(SCHED_OTHER),
            sched_get_priority_max(SCHED_OTHER));
   
     printf("Valid priority range for SCHED_FIFO: %d - %d\n",
            sched_get_priority_min(SCHED_FIFO),
            sched_get_priority_max(SCHED_FIFO));
   
     printf("Valid priority range for SCHED_RR: %d - %d\n",
            sched_get_priority_min(SCHED_RR),
            sched_get_priority_max(SCHED_RR));
     return 0;
   }

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   Note

   If the specified scheduler policy is not known by the system, the function returns -1 and errno is set to EINVAL.

   Note

   Both SCHED_FIFO and SCHED_RR can be any number within the range of 1 to 99. POSIX is not guaranteed to honor this range, however, and portable programs should use these functions.

3. Save the file and exit the editor.

4. Compile the program.

   $ gcc sched_get.c -o msched_get

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Procedure

1. Create the sched_timeslice.c source file and open it in a text editor.

   $ {EDITOR} sched_timeslice.c

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2. Add the following lines to the sched_timeslice.c file.

   #include <stdio.h>
   #include <sched.h>
   
   int main()
   {
      struct timespec ts;
      int ret;
   
      /* real apps must check return values */
      ret = sched_rr_get_interval(0, &ts);
   
      printf("Timeslice: %lu.%lu\n", ts.tv_sec, ts.tv_nsec);
   
      return 0;
   }

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3. Save the file and exit the editor.

4. Compile the program.

   $ gcc sched_timeslice.c -o sched_timeslice

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5. Run the program with varying policies and priorities.

   $ chrt -o 0 ./sched_timeslice
   Timeslice: 0.38994072
   $ chrt -r 10 ./sched_timeslice
   Timeslice: 0.99984800
   $ chrt -f 10 ./sched_timeslice
   Timeslice: 0.0

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Procedure

1. Create the sched_timeslice.c source file and open it in a text editor.

   $ {EDITOR} sched_timeslice.c

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2. Add the following lines to the sched_timeslice.c file.

   #define _GNU_SOURCE
   #include <unistd.h>
   #include <stdio.h>
   #include <stdlib.h>
   #include <string.h>
   #include <time.h>
   #include <linux/unistd.h>
   #include <linux/kernel.h>
   #include <linux/types.h>
   #include <sys/syscall.h>
   #include <pthread.h>
   
   #define gettid() syscall(__NR_gettid)
   
   #define SCHED_DEADLINE    6
   
   /* XXX use the proper syscall numbers */
   #ifdef __x86_64__
   #define __NR_sched_setattr        314
   #define __NR_sched_getattr        315
   #endif
   
   struct sched_attr {
        __u32 size;
        __u32 sched_policy;
        __u64 sched_flags;
   
        /* SCHED_NORMAL, SCHED_BATCH */
        __s32 sched_nice;
   
        /* SCHED_FIFO, SCHED_RR */
        __u32 sched_priority;
   
        /* SCHED_DEADLINE (nsec) */
        __u64 sched_runtime;
        __u64 sched_deadline;
        __u64 sched_period;
   };
   
   int sched_getattr(pid_t pid,
              struct sched_attr *attr,
              unsigned int size,
              unsigned int flags)
   {
        return syscall(__NR_sched_getattr, pid, attr, size, flags);
   }
   
   int main (int argc, char **argv)
   {
        struct sched_attr attr;
        unsigned int flags = 0;
        int ret;
   
        ret = sched_getattr(0, &attr, sizeof(attr), flags);
        if (ret < 0) {
            perror("sched_getattr");
            exit(-1);
        }
   
        printf("main thread pid=%ld\n", gettid());
        printf("main thread policy=%ld\n", attr.sched_policy);
        printf("main thread nice=%ld\n", attr.sched_nice);
        printf("main thread priority=%ld\n", attr.sched_priority);
        printf("main thread runtime=%ld\n", attr.sched_runtime);
        printf("main thread deadline=%ld\n", attr.sched_deadline);
        printf("main thread period=%ld\n", attr.sched_period);
   
        return 0;
   }

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3. Compile the sched_timeslice.c file.

   $ gcc sched_timeslice.c -o sched_timeslice

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4. Check the output of the sched_timeslice program.

   $ ./sched_timeslice
   main thread pid=321716
   main thread policy=6
   main thread nice=0
   main thread priority=0
   main thread runtime=1000000
   main thread deadline=9000000
   main thread period=10000000

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