[PATCH v14 2/2] net: __rte_raw_cksum pointers enable compiler optimizations

scott.k.mitch1
2026-01-12T12:04:27Z

From: Scott Mitchell <scott.k.mitch1@gmail.com>

__rte_raw_cksum uses a loop with memcpy on each iteration.
GCC 15+ is able to vectorize the loop but Clang 18.1 is not.

Replace memcpy with direct pointer access using unaligned_uint16_t.
This enables both GCC and Clang to vectorize the loop while handling
unaligned access safely on all architectures.

Performance results from cksum_perf_autotest on Intel Xeon
(Cascade Lake, AVX-512) built with Clang 18.1 (TSC cycles/byte):

Block size Before After Improvement
100 0.40 0.24 ~40%
1500 0.50 0.06 ~8x
9000 0.49 0.06 ~8x

Signed-off-by: Scott Mitchell <scott.k.mitch1@gmail.com>
---
app/test/meson.build | 1 +
app/test/test_cksum_fuzz.c | 240 +++++++++++++++++++++++++++++++++++++
app/test/test_cksum_perf.c | 2 +-
lib/net/rte_cksum.h | 14 +--
4 files changed, 247 insertions(+), 10 deletions(-)
create mode 100644 app/test/test_cksum_fuzz.c

diff --git a/app/test/meson.build b/app/test/meson.build
index efec42a6bf..c92325ad58 100644
--- a/app/test/meson.build
+++ b/app/test/meson.build
@@ -38,6 +38,7 @@ source_file_deps = {
'test_byteorder.c': [],
'test_cfgfile.c': ['cfgfile'],
'test_cksum.c': ['net'],
+ 'test_cksum_fuzz.c': ['net'],
'test_cksum_perf.c': ['net'],
'test_cmdline.c': [],
'test_cmdline_cirbuf.c': [],
diff --git a/app/test/test_cksum_fuzz.c b/app/test/test_cksum_fuzz.c
new file mode 100644
index 0000000000..839861f57d
--- /dev/null
+++ b/app/test/test_cksum_fuzz.c
@@ -0,0 +1,240 @@
+/* SPDX-License-Identifier: BSD-3-Clause
+ * Copyright(c) 2026 Apple Inc.
+ */
+
+#include <stdio.h>
+#include <string.h>
+
+#include <rte_common.h>
+#include <rte_cycles.h>
+#include <rte_hexdump.h>
+#include <rte_cksum.h>
+#include <rte_malloc.h>
+#include <rte_random.h>
+
+#include "test.h"
+
+/*
+ * Fuzz test for __rte_raw_cksum optimization.
+ * Compares the optimized implementation against the original reference
+ * implementation across random data of various lengths.
+ */
+
+#define DEFAULT_ITERATIONS 1000
+#define MAX_TEST_LEN 65536 /* 64K to match GRO frame sizes */
+
+/*
+ * Original (reference) implementation of __rte_raw_cksum from DPDK v23.11.
+ * This is retained here for comparison testing against the optimized version.
+ */
+static inline uint32_t
+__rte_raw_cksum_reference(const void *buf, size_t len, uint32_t sum)
+{
+ const void *end;
+
+ for (end = RTE_PTR_ADD(buf, RTE_ALIGN_FLOOR(len, sizeof(uint16_t)));
+ buf != end; buf = RTE_PTR_ADD(buf, sizeof(uint16_t))) {
+ uint16_t v;
+
+ memcpy(&v, buf, sizeof(uint16_t));
+ sum += v;
+ }
+
+ /* if length is odd, keeping it byte order independent */
+ if (unlikely(len % 2)) {
+ uint16_t left = 0;
+
+ memcpy(&left, end, 1);
+ sum += left;
+ }
+
+ return sum;
+}
+
+static void
+init_random_buffer(uint8_t *buf, size_t len)
+{
+ size_t i;
+
+ for (i = 0; i < len; i++)
+ buf[i] = (uint8_t)rte_rand();
+}
+
+static inline uint32_t
+get_initial_sum(bool random_initial_sum)
+{
+ return random_initial_sum ? (rte_rand() & 0xFFFFFFFF) : 0;
+}
+
+/*
+ * Test a single buffer length with specific alignment and initial sum
+ */
+static int
+test_cksum_fuzz_length_aligned(size_t len, bool aligned, uint32_t initial_sum)
+{
+ uint8_t *data;
+ uint8_t *buf;
+ size_t alloc_size;
+ uint32_t sum_ref, sum_opt;
+
+ if (len == 0 && !aligned) {
+ /* Skip unaligned test for zero length - nothing to test */
+ return TEST_SUCCESS;
+ }
+
+ /* Allocate exact size for aligned, +1 for unaligned offset */
+ alloc_size = aligned ? len : len + 1;
+ if (alloc_size == 0)
+ alloc_size = 1; /* rte_malloc doesn't like 0 */
+
+ data = rte_malloc(NULL, alloc_size, 64);
+ if (data == NULL) {
+ printf("Failed to allocate %zu bytes\n", alloc_size);
+ return TEST_FAILED;
+ }
+
+ buf = aligned ? data : (data + 1);
+
+ init_random_buffer(buf, len);
+
+ sum_ref = __rte_raw_cksum_reference(buf, len, initial_sum);
+ sum_opt = __rte_raw_cksum(buf, len, initial_sum);
+
+ if (sum_ref != sum_opt) {
+ printf("MISMATCH at len=%zu aligned='%s' initial_sum=0x%08x ref=0x%08x opt=0x%08x\n",
+ len, aligned ? "aligned" : "unaligned",
+ initial_sum, sum_ref, sum_opt);
+ rte_hexdump(stdout, "failing buffer", buf, len);
+ rte_free(data);
+ return TEST_FAILED;
+ }
+
+ rte_free(data);
+ return TEST_SUCCESS;
+}
+
+/*
+ * Test a length with both alignments
+ */
+static int
+test_cksum_fuzz_length(size_t len, uint32_t initial_sum)
+{
+ int rc;
+
+ /* Test aligned */
+ rc = test_cksum_fuzz_length_aligned(len, true, initial_sum);
+ if (rc != TEST_SUCCESS)
+ return rc;
+
+ /* Test unaligned */
+ rc = test_cksum_fuzz_length_aligned(len, false, initial_sum);
+
+ return rc;
+}
+
+/*
+ * Test specific edge case lengths
+ */
+static int
+test_cksum_fuzz_edge_cases(void)
+{
+ /* Edge case lengths that might trigger bugs */
+ static const size_t edge_lengths[] = {
+ 0, 1, 2, 3, 4, 5, 6, 7, 8,
+ 15, 16, 17,
+ 31, 32, 33,
+ 63, 64, 65,
+ 127, 128, 129,
+ 255, 256, 257,
+ 511, 512, 513,
+ 1023, 1024, 1025,
+ 1500, 1501, /* MTU boundaries */
+ 2047, 2048, 2049,
+ 4095, 4096, 4097,
+ 8191, 8192, 8193,
+ 16383, 16384, 16385,
+ 32767, 32768, 32769,
+ 65534, 65535, 65536 /* 64K GRO boundaries */
+ };
+ unsigned int i;
+ int rc;
+
+ printf("Testing edge case lengths...\n");
+
+ for (i = 0; i < RTE_DIM(edge_lengths); i++) {
+ /* Test with zero initial sum */
+ rc = test_cksum_fuzz_length(edge_lengths[i], 0);
+ if (rc != TEST_SUCCESS)
+ return rc;
+
+ /* Test with random initial sum */
+ rc = test_cksum_fuzz_length(edge_lengths[i], get_initial_sum(true));
+ if (rc != TEST_SUCCESS)
+ return rc;
+ }
+
+ return TEST_SUCCESS;
+}
+
+/*
+ * Test random lengths with optional random initial sums
+ */
+static int
+test_cksum_fuzz_random(unsigned int iterations, bool random_initial_sum)
+{
+ unsigned int i;
+ int rc;
+
+ printf("Testing random lengths (0-%d)%s...\n", MAX_TEST_LEN,
+ random_initial_sum ? " with random initial sums" : "");
+
+ for (i = 0; i < iterations; i++) {
+ size_t len = rte_rand() % (MAX_TEST_LEN + 1);
+
+ rc = test_cksum_fuzz_length(len, get_initial_sum(random_initial_sum));
+ if (rc != TEST_SUCCESS) {
+ printf("Failed at len=%zu\n", len);
+ return rc;
+ }
+ }
+
+ return TEST_SUCCESS;
+}
+
+static int
+test_cksum_fuzz(void)
+{
+ int rc;
+ unsigned int iterations = DEFAULT_ITERATIONS;
+ printf("### __rte_raw_cksum optimization fuzz test ###\n");
+ printf("Iterations per test: %u\n\n", iterations);
+
+ /* Test edge cases */
+ rc = test_cksum_fuzz_edge_cases();
+ if (rc != TEST_SUCCESS) {
+ printf("Edge case test FAILED\n");
+ return rc;
+ }
+ printf("Edge case test PASSED\n\n");
+
+ /* Test random lengths with zero initial sum */
+ rc = test_cksum_fuzz_random(iterations, false);
+ if (rc != TEST_SUCCESS) {
+ printf("Random length test FAILED\n");
+ return rc;
+ }
+ printf("Random length test PASSED\n\n");
+
+ /* Test random lengths with random initial sums */
+ rc = test_cksum_fuzz_random(iterations, true);
+ if (rc != TEST_SUCCESS) {
+ printf("Random initial sum test FAILED\n");
+ return rc;
+ }
+ printf("Random initial sum test PASSED\n\n");
+
+ printf("All fuzz tests PASSED!\n");
+ return TEST_SUCCESS;
+}
+
+REGISTER_FAST_TEST(cksum_fuzz_autotest, true, true, test_cksum_fuzz);
diff --git a/app/test/test_cksum_perf.c b/app/test/test_cksum_perf.c
index 0b919cd59f..6b1d4589e0 100644
--- a/app/test/test_cksum_perf.c
+++ b/app/test/test_cksum_perf.c
@@ -15,7 +15,7 @@
#define NUM_BLOCKS 10
#define ITERATIONS 1000000

-static const size_t data_sizes[] = { 20, 21, 100, 101, 1500, 1501 };
+static const size_t data_sizes[] = { 20, 21, 100, 101, 1500, 1501, 9000, 9001, 65536, 65537 };

static __rte_noinline uint16_t
do_rte_raw_cksum(const void *buf, size_t len)
diff --git a/lib/net/rte_cksum.h b/lib/net/rte_cksum.h
index a8e8927952..f04b46a6c3 100644
--- a/lib/net/rte_cksum.h
+++ b/lib/net/rte_cksum.h
@@ -42,15 +42,11 @@ extern "C" {
static inline uint32_t
__rte_raw_cksum(const void *buf, size_t len, uint32_t sum)
{
- const void *end;
-
- for (end = RTE_PTR_ADD(buf, RTE_ALIGN_FLOOR(len, sizeof(uint16_t)));
- buf != end; buf = RTE_PTR_ADD(buf, sizeof(uint16_t))) {
- uint16_t v;
-
- memcpy(&v, buf, sizeof(uint16_t));
- sum += v;
- }
+ /* Process uint16 chunks to preserve overflow/carry math. GCC/Clang vectorize the loop. */
+ const unaligned_uint16_t *buf16 = (const unaligned_uint16_t *)buf;
+ const unaligned_uint16_t *end = buf16 + (len / sizeof(*buf16));
+ for (; buf16 != end; buf16++)
+ sum += *buf16;

/* if length is odd, keeping it byte order independent */
if (unlikely(len % 2)) {
--
2.39.5 (Apple Git-154)