lib/dim: add KUnit test for dim_calc_stats()

Add a KUnit suite for the DIM library that checks the packet, byte,
event and completion rates computed by dim_calc_stats(), including
counter wraparound and windows whose byte or packet count times
USEC_PER_MSEC does not fit in 32 bits. The latter cases fail on 32-bit
architectures without the previous commit.

Assisted-by: LLM
Signed-off-by: Shashank Mohan Jain <jain.sm@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

lib/Kconfig.debug

@@ -2906,6 +2906,21 @@ config LIVEUPDATE_TEST
 
 	  If unsure, say N
 
+config DIMLIB_KUNIT_TEST
+	tristate "KUnit test for the DIM library" if !KUNIT_ALL_TESTS
+	depends on KUNIT && NET
+	select DIMLIB
+	default KUNIT_ALL_TESTS
+	help
+	  This builds the KUnit test for the Dynamic Interrupt Moderation
+	  library (lib/dim/), which checks the rate statistics computed by
+	  dim_calc_stats().
+
+	  For more information on KUnit and unit tests in general please refer
+	  to the KUnit documentation in Documentation/dev-tools/kunit/.
+
+	  If unsure, say N.
+
 config CMDLINE_KUNIT_TEST
 	tristate "KUnit test for cmdline API" if !KUNIT_ALL_TESTS
 	depends on KUNIT

lib/dim/Makefile

@@ -5,3 +5,5 @@
 obj-$(CONFIG_DIMLIB) += dimlib.o
 
 dimlib-y := dim.o net_dim.o rdma_dim.o
+
+obj-$(CONFIG_DIMLIB_KUNIT_TEST) += dim_kunit.o

lib/dim/dim_kunit.c

@@ -0,0 +1,126 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit tests for the Dynamic Interrupt Moderation library
+ */
+
+#include <kunit/test.h>
+#include <linux/dim.h>
+#include <linux/ktime.h>
+#include <linux/module.h>
+
+struct dim_calc_stats_case {
+	const char *name;
+	u32 delta_us;
+	u32 start_pkts, end_pkts;
+	u32 start_bytes, end_bytes;
+	u32 start_comps, end_comps;
+	int ppms, bpms, cpms;
+};
+
+static const struct dim_calc_stats_case dim_calc_stats_cases[] = {
+	{
+		.name = "small",
+		.delta_us = 1000,
+		.end_pkts = 640, .end_bytes = 640 * 1500, .end_comps = 64,
+		.ppms = 640, .bpms = 960000, .cpms = 64,
+	},
+	{
+		.name = "round_up",
+		.delta_us = 3000,
+		.end_pkts = 10, .end_bytes = 10, .end_comps = 1,
+		.ppms = 4, .bpms = 4, .cpms = 1,
+	},
+	{
+		.name = "counter_wrap",
+		.delta_us = 1000,
+		.start_pkts = 0xffffff00, .end_pkts = 0x100,
+		.start_bytes = 0xfffff000, .end_bytes = 0x1000,
+		.start_comps = 0xfffffff0, .end_comps = 0x10,
+		.ppms = 0x200, .bpms = 0x2000, .cpms = 0x20,
+	},
+	{
+		/* 30 MB in 10 ms (24 Gbit/s): nbytes * 1000 exceeds 32 bits */
+		.name = "many_bytes",
+		.delta_us = 10000,
+		.end_pkts = 20000, .end_bytes = 30000000, .end_comps = 64,
+		.ppms = 2000, .bpms = 3000000, .cpms = 7,
+	},
+	{
+		/* 4.3 MB in 16 ms (2.15 Gbit/s), just above the 32-bit limit */
+		.name = "bytes_32bit_limit",
+		.delta_us = 16000,
+		.end_pkts = 2900, .end_bytes = 4300000, .end_comps = 64,
+		.ppms = 182, .bpms = 268750, .cpms = 4,
+	},
+	{
+		/* 5 MB in 40 ms: a 1 Gbit/s link at line rate */
+		.name = "gigabit",
+		.delta_us = 40000,
+		.end_pkts = 3300, .end_bytes = 5000000, .end_comps = 64,
+		.ppms = 83, .bpms = 125000, .cpms = 2,
+	},
+	{
+		/* 5 million packets and completions in 2 s */
+		.name = "many_packets",
+		.delta_us = 2000000,
+		.end_pkts = 5000000, .end_bytes = 5000000, .end_comps = 5000000,
+		.ppms = 2500, .bpms = 2500, .cpms = 2500,
+	},
+};
+
+static void dim_calc_stats_case_desc(const struct dim_calc_stats_case *t,
+				     char *desc)
+{
+	strscpy(desc, t->name, KUNIT_PARAM_DESC_SIZE);
+}
+
+KUNIT_ARRAY_PARAM(dim_calc_stats, dim_calc_stats_cases,
+		  dim_calc_stats_case_desc);
+
+static void dim_calc_stats_test(struct kunit *test)
+{
+	const struct dim_calc_stats_case *t = test->param_value;
+	struct dim_sample start = {}, end = {};
+	struct dim_stats stats = {};
+
+	dim_update_sample_with_comps(0, t->start_pkts, t->start_bytes,
+				     t->start_comps, &start);
+	dim_update_sample_with_comps(DIM_NEVENTS, t->end_pkts, t->end_bytes,
+				     t->end_comps, &end);
+	/* dim_update_sample() stamps ktime_get(); use fixed times instead */
+	start.time = ktime_set(1000, 0);
+	end.time = ktime_add_us(start.time, t->delta_us);
+
+	KUNIT_ASSERT_TRUE(test, dim_calc_stats(&start, &end, &stats));
+	KUNIT_EXPECT_EQ(test, stats.ppms, t->ppms);
+	KUNIT_EXPECT_EQ(test, stats.bpms, t->bpms);
+	KUNIT_EXPECT_EQ(test, stats.cpms, t->cpms);
+	KUNIT_EXPECT_EQ(test, stats.epms,
+			(int)DIV_ROUND_UP(DIM_NEVENTS * USEC_PER_MSEC,
+					  t->delta_us));
+}
+
+static void dim_calc_stats_no_time_test(struct kunit *test)
+{
+	struct dim_sample sample = {};
+	struct dim_stats stats = {};
+
+	dim_update_sample_with_comps(0, 100, 1000, 10, &sample);
+	KUNIT_EXPECT_FALSE(test, dim_calc_stats(&sample, &sample, &stats));
+}
+
+static struct kunit_case dim_test_cases[] = {
+	KUNIT_CASE_PARAM(dim_calc_stats_test, dim_calc_stats_gen_params),
+	KUNIT_CASE(dim_calc_stats_no_time_test),
+	{}
+};
+
+static struct kunit_suite dim_test_suite = {
+	.name = "dim",
+	.test_cases = dim_test_cases,
+};
+
+kunit_test_suite(dim_test_suite);
+
+MODULE_DESCRIPTION("KUnit tests for the DIM library");
+MODULE_LICENSE("GPL");