refperf: Tune reader measurement interval (b864f89f) · Commits · 戴 / test

This commit moves a printk() out of the measurement interval, converts a atomic_dec()/atomic_read() pair to atomic_dec_and_test(), and adds a smp_mb__before_atomic() to avoid potential wake/wait hangs. These changes have the added benefit of reducing the number of loops required for amortizing loop overhead for CONFIG_PREEMPT=n RCU measurements from 1,000,000 to 10,000. This reduction in turn shortens the test, reducing the probability of interference. Cc: Joel Fernandes (Google) <joel@joelfernandes.org> Signed-off-by:

Paul E. McKenney <paulmck@kernel.org>

kernel/rcu/refperf.c

+5 −6

Original line number	Diff line number	Diff line
		@@ -252,15 +252,16 @@ repeat:
		// Make sure that the CPU is affinitized appropriately during testing.
		WARN_ON_ONCE(smp_processor_id() != me);

		smp_mb__before_atomic();
		atomic_dec(&rt->start);

		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().
		local_irq_save(flags);
		start = ktime_get_mono_fast_ns();

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

		cur_ops->readsection(loops);

		duration = ktime_get_mono_fast_ns() - start;
		@@ -268,14 +269,12 @@ repeat:

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

		atomic_dec(&nreaders_exp);
		if (atomic_dec_and_test(&nreaders_exp))
		wake_up(&main_wq);

		VERBOSE_PERFOUT("ref_perf_reader %ld: experiment %d ended, (readers remaining=%d)",
		me, exp_idx, atomic_read(&nreaders_exp));

		if (!atomic_read(&nreaders_exp))
		wake_up(&main_wq);

		if (!torture_must_stop())
		goto repeat;
		end:

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