scheduler tick

먼저 확인할 Linux v6.6 소스 파일

Linux v6.6: kernel/sched/core.c
Linux v6.6: kernel/time/tick-sched.c
Linux v6.6: kernel/sched/fair.c

설명: tick-sched.c의 timer 진입과 NOHZ 중단·재시작, core.c의 공통 tick과 원격 보조 작업, fair.c의 fair 클래스 콜백을 서로 다른 경로로 읽습니다. update_process_times()의 호출 연결은 kernel/time/timer.c에서 확인합니다.

void scheduler_tick(void)

/*
 * This function gets called by the timer code, with HZ frequency.
 * We call it with interrupts disabled.
 */
void scheduler_tick(void)
{
	int cpu = smp_processor_id();
	struct rq *rq = cpu_rq(cpu);
	struct task_struct *curr = rq->curr;
	struct rq_flags rf;
	unsigned long thermal_pressure;
	u64 resched_latency;

	if (housekeeping_cpu(cpu, HK_TYPE_TICK))
		arch_scale_freq_tick();

	sched_clock_tick();

	rq_lock(rq, &rf);

	update_rq_clock(rq);
	thermal_pressure = arch_scale_thermal_pressure(cpu_of(rq));
	update_thermal_load_avg(rq_clock_thermal(rq), rq, thermal_pressure);
	curr->sched_class->task_tick(rq, curr, 0);
	if (sched_feat(LATENCY_WARN))
		resched_latency = cpu_resched_latency(rq);
	calc_global_load_tick(rq);
	sched_core_tick(rq);
	task_tick_mm_cid(rq, curr);

	rq_unlock(rq, &rf);

	if (sched_feat(LATENCY_WARN) && resched_latency)
		resched_latency_warn(cpu, resched_latency);

	perf_event_task_tick();

	if (curr->flags & PF_WQ_WORKER)
		wq_worker_tick(curr);

읽기: rq 잠금 안의 clock 갱신과 클래스 콜백, 잠금 해제 뒤의 계측, 조건부 균형 조정을 구분합니다.

task_tick_fair()

 * NOTE: This function can be called remotely by the tick offload that
 * goes along full dynticks. Therefore no local assumption can be made
 * and everything must be accessed through the @rq and @curr passed in
 * parameters.
 */
static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued)
{
	struct cfs_rq *cfs_rq;
	struct sched_entity *se = &curr->se;

	for_each_sched_entity(se) {
		cfs_rq = cfs_rq_of(se);
		entity_tick(cfs_rq, se, queued);
	}

	if (static_branch_unlikely(&sched_numa_balancing))
		task_tick_numa(rq, curr);

	update_misfit_status(curr, rq);
	update_overutilized_status(task_rq(curr));

	task_tick_core(rq, curr);
}

/*
 * called on fork with the child task as argument from the parent's context
 *  - child not yet on the tasklist
 *  - preemption disabled
 */
static void task_fork_fair(struct task_struct *p)
{
	struct sched_entity *se = &p->se, *curr;
	struct cfs_rq *cfs_rq;
	struct rq *rq = this_rq();
	struct rq_flags rf;

	rq_lock(rq, &rf);
	update_rq_clock(rq);

	cfs_rq = task_cfs_rq(current);

읽기: fair entity별 entity_tick()을 호출합니다. 다른 클래스의 tick 처리와 같다고 일반화하지 않습니다.