linux-kernel - Re: [PATCH v5 20/21] lib: Add trivial kunit test for ratelimit

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Message-ID: <aCISGjo-aYAs8y0u@pathway.suse.cz>
Date: Mon, 12 May 2025 17:22:02 +0200
From: Petr Mladek <pmladek@...e.com>
To: "Paul E. McKenney" <paulmck@...nel.org>
Cc: linux-kernel@...r.kernel.org, kernel-team@...a.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kuniyuki Iwashima <kuniyu@...zon.com>,
	Mateusz Guzik <mjguzik@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	John Ogness <john.ogness@...utronix.de>,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	Jon Pan-Doh <pandoh@...gle.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Karolina Stolarek <karolina.stolarek@...cle.com>
Subject: Re: [PATCH v5 20/21] lib: Add trivial kunit test for ratelimit

On Thu 2025-05-08 16:33:34, Paul E. McKenney wrote:
> Add a simple single-threaded smoke test for lib/ratelimit.c
> 
> To run on x86:
> 
> 	make ARCH=x86_64 mrproper
> 	./tools/testing/kunit/kunit.py run --arch x86_64 --kconfig_add CONFIG_RATELIMIT_KUNIT_TEST=y --kconfig_add CONFIG_SMP=y lib_ratelimit
> 
> This will fail on old ___ratelimit(), and subsequent patches provide
> the fixes that are required.
> 
> --- /dev/null
> +++ b/lib/tests/test_ratelimit.c
> @@ -0,0 +1,79 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +
> +#include <kunit/test.h>
> +
> +#include <linux/ratelimit.h>
> +#include <linux/module.h>
> +
> +/* a simple boot-time regression test */
> +
> +#define TESTRL_INTERVAL (5 * HZ)
> +static DEFINE_RATELIMIT_STATE(testrl, TESTRL_INTERVAL, 3);
> +
> +#define test_ratelimited(test, expected) \
> +	KUNIT_ASSERT_EQ(test, ___ratelimit(&testrl, "test_ratelimit_smoke"), (expected))
> +
> +static void test_ratelimit_smoke(struct kunit *test)
> +{
> +	// Check settings.
> +	KUNIT_ASSERT_GE(test, TESTRL_INTERVAL, 100);
> +
> +	// Test normal operation.
> +	test_ratelimited(test, true);
> +	test_ratelimited(test, true);
> +	test_ratelimited(test, true);
> +	test_ratelimited(test, false);
> +
> +	schedule_timeout_idle(TESTRL_INTERVAL - 40);

Heh, I have got a new laptop. The battery in the previous one was
about to explode. And the test started failing on the next line most
of the time.

The following change helped me:

>From 005e00ca09b4bd5b4a5f3026f1835e0435ecfbd9 Mon Sep 17 00:00:00 2001
From: Petr Mladek <pmladek@...e.com>
Date: Mon, 12 May 2025 16:38:02 +0200
Subject: [PATCH] lib: Make the ratelimit test more reliable

The selftest fails most of the times when running in qemu with
a kernel configured with CONFIG_HZ = 250:

>  test_ratelimit_smoke: 1 callbacks suppressed
>  # test_ratelimit_smoke: ASSERTION FAILED at lib/tests/test_ratelimit.c:28
>                    Expected ___ratelimit(&testrl, "test_ratelimit_smoke") == (false), but
>                        ___ratelimit(&testrl, "test_ratelimit_smoke") == 1 (0x1)
>                        (false) == 0 (0x0)

Try to make the test slightly more reliable by calling the problematic
ratelimit in the middle of the interval.

Signed-off-by: Petr Mladek <pmladek@...e.com>
---
 lib/tests/test_ratelimit.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/lib/tests/test_ratelimit.c b/lib/tests/test_ratelimit.c
index 0374107f5ea8..5d6ec8854600 100644
--- a/lib/tests/test_ratelimit.c
+++ b/lib/tests/test_ratelimit.c
@@ -24,19 +24,19 @@ static void test_ratelimit_smoke(struct kunit *test)
 	test_ratelimited(test, true);
 	test_ratelimited(test, false);
 
-	schedule_timeout_idle(TESTRL_INTERVAL - 40);
+	schedule_timeout_idle(TESTRL_INTERVAL / 2);
 	test_ratelimited(test, false);
 
-	schedule_timeout_idle(50);
+	schedule_timeout_idle(TESTRL_INTERVAL * 3 / 4);
 	test_ratelimited(test, true);
 
 	schedule_timeout_idle(2 * TESTRL_INTERVAL);
 	test_ratelimited(test, true);
 	test_ratelimited(test, true);
 
-	schedule_timeout_idle(TESTRL_INTERVAL - 40);
+	schedule_timeout_idle(TESTRL_INTERVAL / 2 );
 	test_ratelimited(test, true);
-	schedule_timeout_idle(50);
+	schedule_timeout_idle(TESTRL_INTERVAL * 3 / 4);
 	test_ratelimited(test, true);
 	test_ratelimited(test, true);
 	test_ratelimited(test, true);
-- 
2.49.0

Feel free to squash it into the original patch which added the test.

> +	test_ratelimited(test, false);
> +
> +	schedule_timeout_idle(50);
> +	test_ratelimited(test, true);
> +
> +	schedule_timeout_idle(2 * TESTRL_INTERVAL);
> +	test_ratelimited(test, true);
> +	test_ratelimited(test, true);
> +

Best Regards,
Petr