[PATCH v12 3/7] eal: add lcore variable performance test

["Mattias Rönnblom" <mattias.ronnblom@ericsson.com>]

Add basic micro benchmark for lcore variables, in an attempt to assure
that the overhead isn't significantly greater than alternative
approaches, in scenarios where the benefits aren't expected to show up
(i.e., when plenty of cache is available compared to the working set
size of the per-lcore data).

Signed-off-by: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
Acked-by: Chengwen Feng <fengchengwen@huawei.com>
Acked-by: Stephen Hemminger <stephen@networkplumber.org>
Acked-by: Morten Brørup <mb@smartsharesystems.com>

--

PATCH v8:
 * Fix spelling. (Morten Brørup)

PATCH v6:
 * Use floating point math when calculating per-update latency.
   (Morten Brørup)

PATCH v5:
 * Add variant of thread-local storage with initialization performed
   at the time of thread creation to the benchmark scenarios. (Morten
   Brørup)

PATCH v4:
 * Rework the tests to be a little less unrealistic. Instead of a
   single dummy module using a single variable, use a number of
   variables/modules. In this way, differences in cache effects may
   show up.
 * Add RTE_CACHE_GUARD to better mimic that static array pattern.
   (Morten Brørup)
 * Show latencies as TSC cycles. (Morten Brørup)
---
 app/test/meson.build           |   1 +
 app/test/test_lcore_var_perf.c | 257 +++++++++++++++++++++++++++++++++
 2 files changed, 258 insertions(+)
 create mode 100644 app/test/test_lcore_var_perf.c

diff --git a/app/test/meson.build b/app/test/meson.build
index 48279522f0..d4e0c59900 100644
--- a/app/test/meson.build
+++ b/app/test/meson.build
@@ -104,6 +104,7 @@ source_file_deps = {
     'test_kvargs.c': ['kvargs'],
     'test_latencystats.c': ['ethdev', 'latencystats', 'metrics'] + sample_packet_forward_deps,
     'test_lcore_var.c': [],
+    'test_lcore_var_perf.c': [],
     'test_lcores.c': [],
     'test_link_bonding.c': ['ethdev', 'net_bond',
         'net'] + packet_burst_generator_deps + virtual_pmd_deps,
diff --git a/app/test/test_lcore_var_perf.c b/app/test/test_lcore_var_perf.c
new file mode 100644
index 0000000000..2efb8342d1
--- /dev/null
+++ b/app/test/test_lcore_var_perf.c
@@ -0,0 +1,257 @@
+/* SPDX-License-Identifier: BSD-3-Clause
+ * Copyright(c) 2024 Ericsson AB
+ */
+
+#define MAX_MODS 1024
+
+#include <stdio.h>
+
+#include <rte_bitops.h>
+#include <rte_cycles.h>
+#include <rte_lcore_var.h>
+#include <rte_per_lcore.h>
+#include <rte_random.h>
+
+#include "test.h"
+
+struct mod_lcore_state {
+	uint64_t a;
+	uint64_t b;
+	uint64_t sum;
+};
+
+static void
+mod_init(struct mod_lcore_state *state)
+{
+	state->a = rte_rand();
+	state->b = rte_rand();
+	state->sum = 0;
+}
+
+static __rte_always_inline void
+mod_update(volatile struct mod_lcore_state *state)
+{
+	state->sum += state->a * state->b;
+}
+
+struct __rte_cache_aligned mod_lcore_state_aligned {
+	struct mod_lcore_state mod_state;
+
+	RTE_CACHE_GUARD;
+};
+
+static struct mod_lcore_state_aligned
+sarray_lcore_state[MAX_MODS][RTE_MAX_LCORE];
+
+static void
+sarray_init(void)
+{
+	unsigned int lcore_id = rte_lcore_id();
+	int mod;
+
+	for (mod = 0; mod < MAX_MODS; mod++) {
+		struct mod_lcore_state *mod_state =
+			&sarray_lcore_state[mod][lcore_id].mod_state;
+
+		mod_init(mod_state);
+	}
+}
+
+static __rte_noinline void
+sarray_update(unsigned int mod)
+{
+	unsigned int lcore_id = rte_lcore_id();
+	struct mod_lcore_state *mod_state =
+		&sarray_lcore_state[mod][lcore_id].mod_state;
+
+	mod_update(mod_state);
+}
+
+struct mod_lcore_state_lazy {
+	struct mod_lcore_state mod_state;
+	bool initialized;
+};
+
+/*
+ * Note: it's usually a bad idea have this much thread-local storage
+ * allocated in a real application, since it will incur a cost on
+ * thread creation and non-lcore thread memory usage.
+ */
+static RTE_DEFINE_PER_LCORE(struct mod_lcore_state_lazy,
+			    tls_lcore_state)[MAX_MODS];
+
+static inline void
+tls_init(struct mod_lcore_state_lazy *state)
+{
+	mod_init(&state->mod_state);
+
+	state->initialized = true;
+}
+
+static __rte_noinline void
+tls_lazy_update(unsigned int mod)
+{
+	struct mod_lcore_state_lazy *state =
+		&RTE_PER_LCORE(tls_lcore_state[mod]);
+
+	/* With thread-local storage, initialization must usually be lazy */
+	if (!state->initialized)
+		tls_init(state);
+
+	mod_update(&state->mod_state);
+}
+
+static __rte_noinline void
+tls_update(unsigned int mod)
+{
+	struct mod_lcore_state_lazy *state =
+		&RTE_PER_LCORE(tls_lcore_state[mod]);
+
+	mod_update(&state->mod_state);
+}
+
+RTE_LCORE_VAR_HANDLE(struct mod_lcore_state, lvar_lcore_state)[MAX_MODS];
+
+static void
+lvar_init(void)
+{
+	unsigned int mod;
+
+	for (mod = 0; mod < MAX_MODS; mod++) {
+		RTE_LCORE_VAR_ALLOC(lvar_lcore_state[mod]);
+
+		struct mod_lcore_state *state =
+			RTE_LCORE_VAR_VALUE(lvar_lcore_state[mod]);
+
+		mod_init(state);
+	}
+}
+
+static __rte_noinline void
+lvar_update(unsigned int mod)
+{
+	struct mod_lcore_state *state =
+		RTE_LCORE_VAR_VALUE(lvar_lcore_state[mod]);
+
+	mod_update(state);
+}
+
+static void
+shuffle(unsigned int *elems, size_t len)
+{
+	size_t i;
+
+	for (i = len - 1; i > 0; i--) {
+		unsigned int other = rte_rand_max(i + 1);
+
+		unsigned int tmp = elems[other];
+		elems[other] = elems[i];
+		elems[i] = tmp;
+	}
+}
+
+#define ITERATIONS UINT64_C(10000000)
+
+static inline double
+benchmark_access(const unsigned int *mods, unsigned int num_mods,
+		 void (*init_fun)(void), void (*update_fun)(unsigned int))
+{
+	unsigned int i;
+	double start;
+	double end;
+	double latency;
+	unsigned int num_mods_mask = num_mods - 1;
+
+	RTE_VERIFY(rte_is_power_of_2(num_mods));
+
+	if (init_fun != NULL)
+		init_fun();
+
+	/* Warm up cache and make sure TLS variables are initialized */
+	for (i = 0; i < num_mods; i++)
+		update_fun(i);
+
+	start = rte_rdtsc();
+
+	for (i = 0; i < ITERATIONS; i++)
+		update_fun(mods[i & num_mods_mask]);
+
+	end = rte_rdtsc();
+
+	latency = (end - start) / (double)ITERATIONS;
+
+	return latency;
+}
+
+static void
+test_lcore_var_access_n(unsigned int num_mods)
+{
+	double sarray_latency;
+	double tls_latency;
+	double lazy_tls_latency;
+	double lvar_latency;
+	unsigned int mods[num_mods];
+	unsigned int i;
+
+	for (i = 0; i < num_mods; i++)
+		mods[i] = i;
+
+	shuffle(mods, num_mods);
+
+	sarray_latency =
+		benchmark_access(mods, num_mods, sarray_init, sarray_update);
+
+	tls_latency =
+		benchmark_access(mods, num_mods, NULL, tls_update);
+
+	lazy_tls_latency =
+		benchmark_access(mods, num_mods, NULL, tls_lazy_update);
+
+	lvar_latency =
+		benchmark_access(mods, num_mods, lvar_init, lvar_update);
+
+	printf("%17u %8.1f %14.1f %15.1f %10.1f\n", num_mods, sarray_latency,
+	       tls_latency, lazy_tls_latency, lvar_latency);
+}
+
+/*
+ * The potential performance benefit of lcore variables compared to
+ * the use of statically sized, lcore id-indexed arrays is not
+ * shorter latencies in a scenario with low cache pressure, but rather
+ * fewer cache misses in a real-world scenario, with extensive cache
+ * usage. These tests are a crude simulation of such, using <N> dummy
+ * modules, each with a small, per-lcore state. Note however that
+ * these tests have very little non-lcore/thread local state, which is
+ * unrealistic.
+ */
+
+static int
+test_lcore_var_access(void)
+{
+	unsigned int num_mods = 1;
+
+	printf("- Latencies [TSC cycles/update] -\n");
+	printf("Number of           Static   Thread-local    Thread-local      Lcore\n");
+	printf("Modules/Variables    Array        Storage  Storage (Lazy)  Variables\n");
+
+	for (num_mods = 1; num_mods <= MAX_MODS; num_mods *= 2)
+		test_lcore_var_access_n(num_mods);
+
+	return TEST_SUCCESS;
+}
+
+static struct unit_test_suite lcore_var_testsuite = {
+	.suite_name = "lcore variable perf autotest",
+	.unit_test_cases = {
+		TEST_CASE(test_lcore_var_access),
+		TEST_CASES_END()
+	},
+};
+
+static int
+test_lcore_var_perf(void)
+{
+	return unit_test_suite_runner(&lcore_var_testsuite);
+}
+
+REGISTER_PERF_TEST(lcore_var_perf_autotest, test_lcore_var_perf);
-- 
2.43.0