Some alternative schedulers have " yield_type" tunable
From MuQSS description:

This determines what type of yield calls to sched_yield will perform.
 0: No yield.
 1: Yield only to better priority/deadline tasks. (default)
 2: Expire timeslice and recalculate deadline.

From "Project C" (BMQ/PDS) description:

0 - No yield.
1 - Deboost and requeue task. (default)
2 - Set run queue skip task.

I guess "0" is a questionable value (especially with BMQ where my system with a single core and lowest frequency could stuck) but "1" is fine.

So the question is how to implement it with CFS.

In kernel/sched/core.c there's such part
static void do_sched_yield(void)

{
	struct rq_flags rf;
	struct rq *rq;

	rq = this_rq_lock_irq(&rf);

	schedstat_inc(rq->yld_count);
	current->sched_class->yield_task(rq);

	preempt_disable();
	rq_unlock_irq(rq, &rf);
	sched_preempt_enable_no_resched();

	schedule();
}

With "yield_type=0" MuQSS and PrjC put "return" before "rq = this_rq_lock_irq(&rf);"

static void do_sched_yield(void)
{
	struct rq *rq;
	struct rq_flags rf;

	if (!sched_yield_type)
		return;

	rq = this_rq_lock_irq(&rf);

But for "current->sched_class->yield_task(rq);" they have their own code which they use for "yield_type=2"
So is it it safe to just comment
current->sched_class->yield_task(rq);
to get something similar to "yield_type=1" for CFS?