[PATCH v3 02/14] test: scale atomic test based on core count

Stephen Hemminger
2026-01-22T00:54:16Z

The atomic test uses tight spinloops to synchronize worker threads
and performs a fixed 1,000,000 iterations per worker. This causes
two problems on high core count systems:

With many cores (e.g., 32), the massive contention on shared
atomic variables causes the test to exceed the 10 second timeout.

Scale iterations inversely with core count to maintain roughly
constant test duration regardless of system size

With 32 cores, iterations drop from 1,000,000 to 31,250 per worker,
which keeps the test well within the timeout while still providing
meaningful coverage.

Add helper function to test.h so that other similar problems
can be addressed in followon patches.

Bugzilla ID: 952
Fixes: af75078fece3 ("first public release")
Cc: stable@dpdk.org

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
app/test/test.h | 19 ++++++++++++++++
app/test/test_atomic.c | 51 +++++++++++++++++++++++++-----------------
2 files changed, 50 insertions(+), 20 deletions(-)

diff --git a/app/test/test.h b/app/test/test.h
index 10dc45f19d..1f12fc5397 100644
--- a/app/test/test.h
+++ b/app/test/test.h
@@ -12,6 +12,7 @@

#include <rte_hexdump.h>
#include <rte_common.h>
+#include <rte_lcore.h>
#include <rte_os_shim.h>

#define TEST_SUCCESS EXIT_SUCCESS
@@ -223,4 +224,22 @@ void add_test_command(struct test_command *t);
*/
#define REGISTER_ATTIC_TEST REGISTER_TEST_COMMAND

+/**
+ * Scale test iterations inversely with core count.
+ *
+ * On high core count systems, tests with per-core work can exceed
+ * timeout limits due to increased lock contention and scheduling
+ * overhead. This helper scales iterations to keep total test time
+ * roughly constant regardless of core count.
+ *
+ * @param base Base iteration count (used on single-core systems)
+ * @param min Minimum iterations (floor to ensure meaningful testing)
+ * @return Scaled iteration count
+ */
+static inline unsigned int
+test_scale_iterations(unsigned int base, unsigned int min)
+{
+ return RTE_MAX(base / rte_lcore_count(), min);
+}
+
#endif
diff --git a/app/test/test_atomic.c b/app/test/test_atomic.c
index b1a0d40ece..2a4531b833 100644
--- a/app/test/test_atomic.c
+++ b/app/test/test_atomic.c
@@ -10,6 +10,7 @@
#include <sys/queue.h>

#include <rte_memory.h>
+#include <rte_common.h>
#include <rte_per_lcore.h>
#include <rte_launch.h>
#include <rte_atomic.h>
@@ -101,7 +102,15 @@

#define NUM_ATOMIC_TYPES 3

-#define N 1000000
+#define N_BASE 1000000u
+#define N_MIN 10000u
+
+/*
+ * Number of iterations for each test, scaled inversely with core count.
+ * More cores means more contention which increases time per operation.
+ * Calculated once at test start to avoid repeated computation in workers.
+ */
+static unsigned int num_iterations;

static rte_atomic16_t a16;
static rte_atomic32_t a32;
@@ -112,36 +121,36 @@ static rte_atomic32_t synchro;
static int
test_atomic_usual(__rte_unused void *arg)
{
- unsigned i;
+ unsigned int i;

while (rte_atomic32_read(&synchro) == 0)
rte_pause();

- for (i = 0; i < N; i++)
+ for (i = 0; i < num_iterations; i++)
rte_atomic16_inc(&a16);
- for (i = 0; i < N; i++)
+ for (i = 0; i < num_iterations; i++)
rte_atomic16_dec(&a16);
- for (i = 0; i < (N / 5); i++)
+ for (i = 0; i < (num_iterations / 5); i++)
rte_atomic16_add(&a16, 5);
- for (i = 0; i < (N / 5); i++)
+ for (i = 0; i < (num_iterations / 5); i++)
rte_atomic16_sub(&a16, 5);

- for (i = 0; i < N; i++)
+ for (i = 0; i < num_iterations; i++)
rte_atomic32_inc(&a32);
- for (i = 0; i < N; i++)
+ for (i = 0; i < num_iterations; i++)
rte_atomic32_dec(&a32);
- for (i = 0; i < (N / 5); i++)
+ for (i = 0; i < (num_iterations / 5); i++)
rte_atomic32_add(&a32, 5);
- for (i = 0; i < (N / 5); i++)
+ for (i = 0; i < (num_iterations / 5); i++)
rte_atomic32_sub(&a32, 5);

- for (i = 0; i < N; i++)
+ for (i = 0; i < num_iterations; i++)
rte_atomic64_inc(&a64);
- for (i = 0; i < N; i++)
+ for (i = 0; i < num_iterations; i++)
rte_atomic64_dec(&a64);
- for (i = 0; i < (N / 5); i++)
+ for (i = 0; i < (num_iterations / 5); i++)
rte_atomic64_add(&a64, 5);
- for (i = 0; i < (N / 5); i++)
+ for (i = 0; i < (num_iterations / 5); i++)
rte_atomic64_sub(&a64, 5);

return 0;
@@ -169,12 +178,12 @@ test_atomic_addsub_and_return(__rte_unused void *arg)
uint32_t tmp16;
uint32_t tmp32;
uint64_t tmp64;
- unsigned i;
+ unsigned int i;

while (rte_atomic32_read(&synchro) == 0)
rte_pause();

- for (i = 0; i < N; i++) {
+ for (i = 0; i < num_iterations; i++) {
tmp16 = rte_atomic16_add_return(&a16, 1);
rte_atomic64_add(&count, tmp16);

@@ -274,7 +283,7 @@ test_atomic128_cmp_exchange(__rte_unused void *arg)

expected = count128;

- for (i = 0; i < N; i++) {
+ for (i = 0; i < num_iterations; i++) {
do {
rte_int128_t desired;

@@ -401,7 +410,7 @@ get_crc8(uint8_t *message, int length)
static int
test_atomic_exchange(__rte_unused void *arg)
{
- int i;
+ unsigned int i;
test16_t nt16, ot16; /* new token, old token */
test32_t nt32, ot32;
test64_t nt64, ot64;
@@ -417,7 +426,7 @@ test_atomic_exchange(__rte_unused void *arg)
* appropriate crc32 hash for the data) then the test iteration has
* passed. If the token is invalid, increment the counter.
*/
- for (i = 0; i < N; i++) {
+ for (i = 0; i < num_iterations; i++) {

/* Test 64bit Atomic Exchange */
nt64.u64 = rte_rand();
@@ -446,6 +455,8 @@ test_atomic_exchange(__rte_unused void *arg)
static int
test_atomic(void)
{
+ num_iterations = test_scale_iterations(N_BASE, N_MIN);
+
rte_atomic16_init(&a16);
rte_atomic32_init(&a32);
rte_atomic64_init(&a64);
@@ -593,7 +604,7 @@ test_atomic(void)
rte_atomic32_clear(&synchro);

iterations = count128.val[0] - count128.val[1];
- if (iterations != (uint64_t)4*N*(rte_lcore_count()-1)) {
+ if (iterations != (uint64_t)4*num_iterations*(rte_lcore_count()-1)) {
printf("128-bit compare and swap failed\n");
return -1;
}
--
2.51.0