sched_deadline.cc

namespace {

extern "C" {

#include <linux/sched.h>
#include <linux/kernel.h>
#include <unistd.h>
#include <sys/syscall.h>
#include <linux/types.h>
#include <sched.h>
#include <linux/sched.h>
#include <sys/types.h>

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 */
    __u64 sched_runtime;
    __u64 sched_deadline;
    __u64 sched_period;
};

int sched_setattr(
    pid_t pid, const struct sched_attr *attr, unsigned int flags) {
  return syscall(__NR_sched_setattr, pid, attr, flags);
}

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);
}

}  // extern "C"

}  // namespace

#include <sys/time.h>
#include <iostream>
#include <cstring>

void loop() {
  static uint64_t s_prev_us = 0;
  struct timeval tv;
  gettimeofday(&tv, nullptr);
  uint64_t us = tv.tv_sec * 1E6 + tv.tv_usec;
  std::cout << "Now: " << us / 1000 << " diff (us): " << us - s_prev_us << std::endl;
  s_prev_us = us;
  return;
}

int set_scheduler_to_deadline() {
  const uint64_t ms_in_ns = 1000000;
  sched_attr attr {
      .size = sizeof(sched_attr),
      .sched_policy = SCHED_DEADLINE,
      .sched_flags = SCHED_FLAG_RESET_ON_FORK,
      .sched_nice = 0 /* Not used for DEADLINE. */,
      .sched_priority = 0 /* Not used for DEADLINE. */,
      .sched_runtime = 1 * ms_in_ns /* 1 ms */,
      .sched_deadline = 2 * ms_in_ns /* 2 ms */,
      .sched_period = 10 * ms_in_ns /* 10 ms */
  };
  return sched_setattr(0 /* pid */, &attr, 0 /* flags */);
}

int main() {
  int rc = set_scheduler_to_deadline();
  if (rc != 0) {
    std::cerr << "Failed to set schedular params: "
                << strerror(errno) << std::endl;
    return 1;
  }
  std::cout << "Set the schedular to DEADLINE." << std::endl;

  while (true) {
    loop();
    sched_yield();
  }

  return 0;
}