refperf: Add warmup and cooldown processing phases

// Use to wait for all threads to start.

static atomic_t n_init;

static atomic_t n_started;

static atomic_t n_warmedup;

static atomic_t n_cooleddown;

// Track which experiment is currently running.

static int exp_idx;

	VERBOSE_PERFOUT("ref_perf_reader %ld: experiment %d started", me, exp_idx);

	// To prevent noise, keep interrupts disabled. This also has the

	// effect of preventing entries into slow path for rcu_read_unlock().

	// To reduce noise, do an initial cache-warming invocation, check

	// in, and then keep warming until everyone has checked in.

	cur_ops->readsection(loops);

	if (!atomic_dec_return(&n_warmedup))

		while (atomic_read_acquire(&n_warmedup))

			cur_ops->readsection(loops);

	// Also keep interrupts disabled.  This also has the effect

	// of preventing entries into slow path for rcu_read_unlock().

	local_irq_save(flags);

	start = ktime_get_mono_fast_ns();

	local_irq_restore(flags);

	rt->last_duration_ns = WARN_ON_ONCE(duration < 0) ? 0 : duration;

	// To reduce runtime-skew noise, do maintain-load invocations until

	// everyone is done.

	if (!atomic_dec_return(&n_cooleddown))

		while (atomic_read_acquire(&n_cooleddown))

			cur_ops->readsection(loops);

	if (atomic_dec_and_test(&nreaders_exp))

		wake_up(&main_wq);

		reset_readers();

		atomic_set(&nreaders_exp, nreaders);

		atomic_set(&n_started, nreaders);

		atomic_set(&n_warmedup, nreaders);

		atomic_set(&n_cooleddown, nreaders);

		exp_idx = exp;