[PATCH v11] net: optimize raw checksum computation

[PATCH v11] net: optimize raw checksum computation

[scott.k.mitch1]

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.
Replacing the memcpy with unaligned_uint16_t pointer access enables
both GCC and Clang to vectorize with SSE/AVX/AVX-512.

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>
---
Changes in v11:
- Fixed patch format: v8-v10 had malformed hunk headers that prevented
  git am from applying the patch. v11 uses unmodified git format-patch
  output.

Changes in v10:
- Fixed patch metadata format: removed literal separator markers from v9
  changelog text that would be interpreted as patch delimiters.

Changes in v9:
- Fixed patch metadata format: v8 had duplicate separator which caused
  changelog to not render on patches.dpdk.org.

Changes in v8:
- __rte_raw_cksum: use native pointer arithmetic instead of RTE_PTR_ADD
  to avoid incorrect results with -O3 for UDP checksums. Also improves
  performance due to less assembly generated with Clang.
- Added __rte_no_ubsan_alignment attribute to suppress false UBSAN warnings
- Added RTE_SUPPRESS_UNINITIALIZED_WARNING macro for GCC workaround
- Fixed C++ compilation errors in rte_ip4.h and rte_ip6.h
- Formatted complex ternary expressions for readability

Changes in v7:
- Replaced pointer arithmetic with RTE_PTR_ADD/RTE_ALIGN_FLOOR for DPDK consistency
  (BROKEN - Clang alias analysis bug causes incorrect UDP checksums)

Changes in v6:
- Fixed GCC -Wmaybe-uninitialized false positive in mlx5 driver

Changes in v5:
- Replaced memcpy loop with direct pointer access to enable vectorization
- Fixed GCC -Wmaybe-uninitialized false-positive warnings in rte_ipv4_phdr_cksum
  and rte_ipv6_phdr_cksum using compiler barriers (no assembly impact)
- Refactored hinic driver's local phdr_cksum implementations to call common
  functions, eliminating duplication
- Simplified phdr_cksum struct initialization with designated initializers

Changes in v4:
- Replaced manual 64-byte loop unrolling with simple pointer iteration
- Removed __rte_no_ubsan_alignment macro (no longer needed)
- Removed rte_ip6.h false-positive warning fix (unable to repro locally)
- Updated performance numbers: AVX-512 vectorization on Clang achieves ~8x
  improvement for large packets vs scalar implementation

Changes in v3:
- Added __rte_no_ubsan_alignment macro to suppress false-positive UBSAN
  alignment warnings when using unaligned_uint16_t
- Fixed false-positive GCC maybe-uninitialized warning in rte_ip6.h exposed
  by optimization (can be split to separate patch once verified on CI)

Changes in v2:
- Fixed UndefinedBehaviorSanitizer errors by adding uint32_t casts to prevent
  signed integer overflow in addition chains
- Restored uint32_t sum accumulator instead of uint64_t
- Added 64k length to test_cksum_perf.c

 app/test/meson.build             |   1 +
 app/test/test_cksum_fuzz.c       | 240 +++++++++++++++++++++++++++++++
 app/test/test_cksum_perf.c       |   2 +-
 drivers/net/hinic/hinic_pmd_tx.c |  38 +----
 drivers/net/mlx5/mlx5_flow_dv.c  |   2 +
 lib/eal/include/rte_common.h     |  22 +++
 lib/net/rte_cksum.h              |  18 +--
 lib/net/rte_ip4.h                |  26 ++--
 lib/net/rte_ip6.h                |  17 ++-
 9 files changed, 294 insertions(+), 72 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/drivers/net/hinic/hinic_pmd_tx.c b/drivers/net/hinic/hinic_pmd_tx.c
index 22fb0bffaf..6b36ad84fd 100644
--- a/drivers/net/hinic/hinic_pmd_tx.c
+++ b/drivers/net/hinic/hinic_pmd_tx.c
@@ -706,47 +706,13 @@ hinic_get_sq_wqe(struct hinic_txq *txq, int wqebb_cnt,
 static inline uint16_t
 hinic_ipv4_phdr_cksum(const struct rte_ipv4_hdr *ipv4_hdr, uint64_t ol_flags)
 {
-	struct ipv4_psd_header {
-		uint32_t src_addr; /* IP address of source host. */
-		uint32_t dst_addr; /* IP address of destination host. */
-		uint8_t  zero;     /* zero. */
-		uint8_t  proto;    /* L4 protocol type. */
-		uint16_t len;      /* L4 length. */
-	} psd_hdr;
-
-	psd_hdr.src_addr = ipv4_hdr->src_addr;
-	psd_hdr.dst_addr = ipv4_hdr->dst_addr;
-	psd_hdr.zero = 0;
-	psd_hdr.proto = ipv4_hdr->next_proto_id;
-	if (ol_flags & RTE_MBUF_F_TX_TCP_SEG) {
-		psd_hdr.len = 0;
-	} else {
-		psd_hdr.len =
-		rte_cpu_to_be_16(rte_be_to_cpu_16(ipv4_hdr->total_length) -
-				 rte_ipv4_hdr_len(ipv4_hdr));
-	}
-	return rte_raw_cksum(&psd_hdr, sizeof(psd_hdr));
+	return rte_ipv4_phdr_cksum(ipv4_hdr, ol_flags & RTE_MBUF_F_TX_TCP_SEG);
 }
 
 static inline uint16_t
 hinic_ipv6_phdr_cksum(const struct rte_ipv6_hdr *ipv6_hdr, uint64_t ol_flags)
 {
-	uint32_t sum;
-	struct {
-		uint32_t len;   /* L4 length. */
-		uint32_t proto; /* L4 protocol - top 3 bytes must be zero */
-	} psd_hdr;
-
-	psd_hdr.proto = (ipv6_hdr->proto << 24);
-	if (ol_flags & RTE_MBUF_F_TX_TCP_SEG)
-		psd_hdr.len = 0;
-	else
-		psd_hdr.len = ipv6_hdr->payload_len;
-
-	sum = __rte_raw_cksum(&ipv6_hdr->src_addr,
-		sizeof(ipv6_hdr->src_addr) + sizeof(ipv6_hdr->dst_addr), 0);
-	sum = __rte_raw_cksum(&psd_hdr, sizeof(psd_hdr), sum);
-	return __rte_raw_cksum_reduce(sum);
+	return rte_ipv6_phdr_cksum(ipv6_hdr, ol_flags & RTE_MBUF_F_TX_TCP_SEG);
 }
 
 static inline void hinic_get_outer_cs_pld_offset(struct rte_mbuf *m,
diff --git a/drivers/net/mlx5/mlx5_flow_dv.c b/drivers/net/mlx5/mlx5_flow_dv.c
index 47f6d28410..4f77a1e4f1 100644
--- a/drivers/net/mlx5/mlx5_flow_dv.c
+++ b/drivers/net/mlx5/mlx5_flow_dv.c
@@ -4445,6 +4445,8 @@ __flow_encap_decap_resource_register(struct rte_eth_dev *dev,
 			.reserve = 0,
 		}
 	};
+	RTE_SUPPRESS_UNINITIALIZED_WARNING(encap_decap_key);
+
 	struct mlx5_flow_cb_ctx ctx = {
 		.error = error,
 		.data = resource,
diff --git a/lib/eal/include/rte_common.h b/lib/eal/include/rte_common.h
index 9e7d84f929..044275c2bd 100644
--- a/lib/eal/include/rte_common.h
+++ b/lib/eal/include/rte_common.h
@@ -546,6 +546,28 @@ static void __attribute__((destructor(RTE_PRIO(prio)), used)) func(void)
 #define __rte_no_asan
 #endif
 
+/**
+ * Disable UndefinedBehaviorSanitizer alignment check on some code
+ */
+#if defined(RTE_CC_CLANG) || defined(RTE_CC_GCC)
+#define __rte_no_ubsan_alignment __attribute__((no_sanitize("alignment")))
+#else
+#define __rte_no_ubsan_alignment
+#endif
+
+/**
+ * Suppress GCC -Wmaybe-uninitialized false positive on struct initialization.
+ * This tells the compiler that the variable's memory has been touched,
+ * preventing the false positive without affecting other optimizations.
+ */
+#ifdef RTE_CC_GCC
+#define RTE_SUPPRESS_UNINITIALIZED_WARNING(var) do {	\
+	asm volatile("" : "+m" (var));			\
+} while (0)
+#else
+#define RTE_SUPPRESS_UNINITIALIZED_WARNING(var)
+#endif
+
 /*********** Macros for pointer arithmetic ********/
 
 /**
diff --git a/lib/net/rte_cksum.h b/lib/net/rte_cksum.h
index a8e8927952..364f519455 100644
--- a/lib/net/rte_cksum.h
+++ b/lib/net/rte_cksum.h
@@ -39,23 +39,19 @@ extern "C" {
  * @return
  *   sum += Sum of all words in the buffer.
  */
+__rte_no_ubsan_alignment
 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(uint16_t));
+	for (; buf16 != end; buf16++)
+		sum += *buf16;
 
 	/* if length is odd, keeping it byte order independent */
-	if (unlikely(len % 2)) {
+	if (len & 1) {
 		uint16_t left = 0;
-
 		memcpy(&left, end, 1);
 		sum += left;
 	}
diff --git a/lib/net/rte_ip4.h b/lib/net/rte_ip4.h
index 822a660cfb..63852717c9 100644
--- a/lib/net/rte_ip4.h
+++ b/lib/net/rte_ip4.h
@@ -223,21 +223,17 @@ rte_ipv4_phdr_cksum(const struct rte_ipv4_hdr *ipv4_hdr, uint64_t ol_flags)
 		uint8_t  zero;     /* zero. */
 		uint8_t  proto;    /* L4 protocol type. */
 		uint16_t len;      /* L4 length. */
-	} psd_hdr;
-
-	uint32_t l3_len;
-
-	psd_hdr.src_addr = ipv4_hdr->src_addr;
-	psd_hdr.dst_addr = ipv4_hdr->dst_addr;
-	psd_hdr.zero = 0;
-	psd_hdr.proto = ipv4_hdr->next_proto_id;
-	if (ol_flags & (RTE_MBUF_F_TX_TCP_SEG | RTE_MBUF_F_TX_UDP_SEG)) {
-		psd_hdr.len = 0;
-	} else {
-		l3_len = rte_be_to_cpu_16(ipv4_hdr->total_length);
-		psd_hdr.len = rte_cpu_to_be_16((uint16_t)(l3_len -
-			rte_ipv4_hdr_len(ipv4_hdr)));
-	}
+	} psd_hdr = {
+		.src_addr = ipv4_hdr->src_addr,
+		.dst_addr = ipv4_hdr->dst_addr,
+		.proto = ipv4_hdr->next_proto_id,
+		.len = (ol_flags & (RTE_MBUF_F_TX_TCP_SEG | RTE_MBUF_F_TX_UDP_SEG))
+			? (uint16_t)0
+			: rte_cpu_to_be_16((uint16_t)(rte_be_to_cpu_16(ipv4_hdr->total_length) -
+					rte_ipv4_hdr_len(ipv4_hdr)))
+	};
+	RTE_SUPPRESS_UNINITIALIZED_WARNING(psd_hdr);
+
 	return rte_raw_cksum(&psd_hdr, sizeof(psd_hdr));
 }
 
diff --git a/lib/net/rte_ip6.h b/lib/net/rte_ip6.h
index d1abf1f5d5..8a7e5e4b8a 100644
--- a/lib/net/rte_ip6.h
+++ b/lib/net/rte_ip6.h
@@ -560,19 +560,18 @@ rte_ipv6_phdr_cksum(const struct rte_ipv6_hdr *ipv6_hdr, uint64_t ol_flags)
 static inline uint16_t
 rte_ipv6_phdr_cksum(const struct rte_ipv6_hdr *ipv6_hdr, uint64_t ol_flags)
 {
-	uint32_t sum;
 	struct {
 		rte_be32_t len;   /* L4 length. */
 		rte_be32_t proto; /* L4 protocol - top 3 bytes must be zero */
-	} psd_hdr;
-
-	psd_hdr.proto = (uint32_t)(ipv6_hdr->proto << 24);
-	if (ol_flags & (RTE_MBUF_F_TX_TCP_SEG | RTE_MBUF_F_TX_UDP_SEG))
-		psd_hdr.len = 0;
-	else
-		psd_hdr.len = ipv6_hdr->payload_len;
+	} psd_hdr = {
+		.len = (ol_flags & (RTE_MBUF_F_TX_TCP_SEG | RTE_MBUF_F_TX_UDP_SEG))
+			? (rte_be32_t)0
+			: ipv6_hdr->payload_len,
+		.proto = (uint32_t)(ipv6_hdr->proto << 24)
+	};
+	RTE_SUPPRESS_UNINITIALIZED_WARNING(psd_hdr);
 
-	sum = __rte_raw_cksum(&ipv6_hdr->src_addr,
+	uint32_t sum = __rte_raw_cksum(&ipv6_hdr->src_addr,
 		sizeof(ipv6_hdr->src_addr) + sizeof(ipv6_hdr->dst_addr),
 		0);
 	sum = __rte_raw_cksum(&psd_hdr, sizeof(psd_hdr), sum);
-- 
2.39.5 (Apple Git-154)

Re: [PATCH v11] net: optimize raw checksum computation

[Scott Mitchell]

DTS test_checksum_offload_with_vlan failed
(https://mails.dpdk.org/archives/test-report/2026-January/944616.html)
but I also see other examples where this test failed:
1. https://mails.dpdk.org/archives/test-report/2026-January/943627.html
2. https://mails.dpdk.org/archives/test-report/2026-January/943587.html

Is this a known flaky test?

On Thu, Jan 8, 2026 at 6:05 PM <scott.k.mitch1@gmail.com> wrote:
>
> 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.
> Replacing the memcpy with unaligned_uint16_t pointer access enables
> both GCC and Clang to vectorize with SSE/AVX/AVX-512.
>
> 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>
> ---
> Changes in v11:
> - Fixed patch format: v8-v10 had malformed hunk headers that prevented
>   git am from applying the patch. v11 uses unmodified git format-patch
>   output.
>
> Changes in v10:
> - Fixed patch metadata format: removed literal separator markers from v9
>   changelog text that would be interpreted as patch delimiters.
>
> Changes in v9:
> - Fixed patch metadata format: v8 had duplicate separator which caused
>   changelog to not render on patches.dpdk.org.
>
> Changes in v8:
> - __rte_raw_cksum: use native pointer arithmetic instead of RTE_PTR_ADD
>   to avoid incorrect results with -O3 for UDP checksums. Also improves
>   performance due to less assembly generated with Clang.
> - Added __rte_no_ubsan_alignment attribute to suppress false UBSAN warnings
> - Added RTE_SUPPRESS_UNINITIALIZED_WARNING macro for GCC workaround
> - Fixed C++ compilation errors in rte_ip4.h and rte_ip6.h
> - Formatted complex ternary expressions for readability
>
> Changes in v7:
> - Replaced pointer arithmetic with RTE_PTR_ADD/RTE_ALIGN_FLOOR for DPDK consistency
>   (BROKEN - Clang alias analysis bug causes incorrect UDP checksums)
>
> Changes in v6:
> - Fixed GCC -Wmaybe-uninitialized false positive in mlx5 driver
>
> Changes in v5:
> - Replaced memcpy loop with direct pointer access to enable vectorization
> - Fixed GCC -Wmaybe-uninitialized false-positive warnings in rte_ipv4_phdr_cksum
>   and rte_ipv6_phdr_cksum using compiler barriers (no assembly impact)
> - Refactored hinic driver's local phdr_cksum implementations to call common
>   functions, eliminating duplication
> - Simplified phdr_cksum struct initialization with designated initializers
>
> Changes in v4:
> - Replaced manual 64-byte loop unrolling with simple pointer iteration
> - Removed __rte_no_ubsan_alignment macro (no longer needed)
> - Removed rte_ip6.h false-positive warning fix (unable to repro locally)
> - Updated performance numbers: AVX-512 vectorization on Clang achieves ~8x
>   improvement for large packets vs scalar implementation
>
> Changes in v3:
> - Added __rte_no_ubsan_alignment macro to suppress false-positive UBSAN
>   alignment warnings when using unaligned_uint16_t
> - Fixed false-positive GCC maybe-uninitialized warning in rte_ip6.h exposed
>   by optimization (can be split to separate patch once verified on CI)
>
> Changes in v2:
> - Fixed UndefinedBehaviorSanitizer errors by adding uint32_t casts to prevent
>   signed integer overflow in addition chains
> - Restored uint32_t sum accumulator instead of uint64_t
> - Added 64k length to test_cksum_perf.c
>
>  app/test/meson.build             |   1 +
>  app/test/test_cksum_fuzz.c       | 240 +++++++++++++++++++++++++++++++
>  app/test/test_cksum_perf.c       |   2 +-
>  drivers/net/hinic/hinic_pmd_tx.c |  38 +----
>  drivers/net/mlx5/mlx5_flow_dv.c  |   2 +
>  lib/eal/include/rte_common.h     |  22 +++
>  lib/net/rte_cksum.h              |  18 +--
>  lib/net/rte_ip4.h                |  26 ++--
>  lib/net/rte_ip6.h                |  17 ++-
>  9 files changed, 294 insertions(+), 72 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/drivers/net/hinic/hinic_pmd_tx.c b/drivers/net/hinic/hinic_pmd_tx.c
> index 22fb0bffaf..6b36ad84fd 100644
> --- a/drivers/net/hinic/hinic_pmd_tx.c
> +++ b/drivers/net/hinic/hinic_pmd_tx.c
> @@ -706,47 +706,13 @@ hinic_get_sq_wqe(struct hinic_txq *txq, int wqebb_cnt,
>  static inline uint16_t
>  hinic_ipv4_phdr_cksum(const struct rte_ipv4_hdr *ipv4_hdr, uint64_t ol_flags)
>  {
> -       struct ipv4_psd_header {
> -               uint32_t src_addr; /* IP address of source host. */
> -               uint32_t dst_addr; /* IP address of destination host. */
> -               uint8_t  zero;     /* zero. */
> -               uint8_t  proto;    /* L4 protocol type. */
> -               uint16_t len;      /* L4 length. */
> -       } psd_hdr;
> -
> -       psd_hdr.src_addr = ipv4_hdr->src_addr;
> -       psd_hdr.dst_addr = ipv4_hdr->dst_addr;
> -       psd_hdr.zero = 0;
> -       psd_hdr.proto = ipv4_hdr->next_proto_id;
> -       if (ol_flags & RTE_MBUF_F_TX_TCP_SEG) {
> -               psd_hdr.len = 0;
> -       } else {
> -               psd_hdr.len =
> -               rte_cpu_to_be_16(rte_be_to_cpu_16(ipv4_hdr->total_length) -
> -                                rte_ipv4_hdr_len(ipv4_hdr));
> -       }
> -       return rte_raw_cksum(&psd_hdr, sizeof(psd_hdr));
> +       return rte_ipv4_phdr_cksum(ipv4_hdr, ol_flags & RTE_MBUF_F_TX_TCP_SEG);
>  }
>
>  static inline uint16_t
>  hinic_ipv6_phdr_cksum(const struct rte_ipv6_hdr *ipv6_hdr, uint64_t ol_flags)
>  {
> -       uint32_t sum;
> -       struct {
> -               uint32_t len;   /* L4 length. */
> -               uint32_t proto; /* L4 protocol - top 3 bytes must be zero */
> -       } psd_hdr;
> -
> -       psd_hdr.proto = (ipv6_hdr->proto << 24);
> -       if (ol_flags & RTE_MBUF_F_TX_TCP_SEG)
> -               psd_hdr.len = 0;
> -       else
> -               psd_hdr.len = ipv6_hdr->payload_len;
> -
> -       sum = __rte_raw_cksum(&ipv6_hdr->src_addr,
> -               sizeof(ipv6_hdr->src_addr) + sizeof(ipv6_hdr->dst_addr), 0);
> -       sum = __rte_raw_cksum(&psd_hdr, sizeof(psd_hdr), sum);
> -       return __rte_raw_cksum_reduce(sum);
> +       return rte_ipv6_phdr_cksum(ipv6_hdr, ol_flags & RTE_MBUF_F_TX_TCP_SEG);
>  }
>
>  static inline void hinic_get_outer_cs_pld_offset(struct rte_mbuf *m,
> diff --git a/drivers/net/mlx5/mlx5_flow_dv.c b/drivers/net/mlx5/mlx5_flow_dv.c
> index 47f6d28410..4f77a1e4f1 100644
> --- a/drivers/net/mlx5/mlx5_flow_dv.c
> +++ b/drivers/net/mlx5/mlx5_flow_dv.c
> @@ -4445,6 +4445,8 @@ __flow_encap_decap_resource_register(struct rte_eth_dev *dev,
>                         .reserve = 0,
>                 }
>         };
> +       RTE_SUPPRESS_UNINITIALIZED_WARNING(encap_decap_key);
> +
>         struct mlx5_flow_cb_ctx ctx = {
>                 .error = error,
>                 .data = resource,
> diff --git a/lib/eal/include/rte_common.h b/lib/eal/include/rte_common.h
> index 9e7d84f929..044275c2bd 100644
> --- a/lib/eal/include/rte_common.h
> +++ b/lib/eal/include/rte_common.h
> @@ -546,6 +546,28 @@ static void __attribute__((destructor(RTE_PRIO(prio)), used)) func(void)
>  #define __rte_no_asan
>  #endif
>
> +/**
> + * Disable UndefinedBehaviorSanitizer alignment check on some code
> + */
> +#if defined(RTE_CC_CLANG) || defined(RTE_CC_GCC)
> +#define __rte_no_ubsan_alignment __attribute__((no_sanitize("alignment")))
> +#else
> +#define __rte_no_ubsan_alignment
> +#endif
> +
> +/**
> + * Suppress GCC -Wmaybe-uninitialized false positive on struct initialization.
> + * This tells the compiler that the variable's memory has been touched,
> + * preventing the false positive without affecting other optimizations.
> + */
> +#ifdef RTE_CC_GCC
> +#define RTE_SUPPRESS_UNINITIALIZED_WARNING(var) do {   \
> +       asm volatile("" : "+m" (var));                  \
> +} while (0)
> +#else
> +#define RTE_SUPPRESS_UNINITIALIZED_WARNING(var)
> +#endif
> +
>  /*********** Macros for pointer arithmetic ********/
>
>  /**
> diff --git a/lib/net/rte_cksum.h b/lib/net/rte_cksum.h
> index a8e8927952..364f519455 100644
> --- a/lib/net/rte_cksum.h
> +++ b/lib/net/rte_cksum.h
> @@ -39,23 +39,19 @@ extern "C" {
>   * @return
>   *   sum += Sum of all words in the buffer.
>   */
> +__rte_no_ubsan_alignment
>  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(uint16_t));
> +       for (; buf16 != end; buf16++)
> +               sum += *buf16;
>
>         /* if length is odd, keeping it byte order independent */
> -       if (unlikely(len % 2)) {
> +       if (len & 1) {
>                 uint16_t left = 0;
> -
>                 memcpy(&left, end, 1);
>                 sum += left;
>         }
> diff --git a/lib/net/rte_ip4.h b/lib/net/rte_ip4.h
> index 822a660cfb..63852717c9 100644
> --- a/lib/net/rte_ip4.h
> +++ b/lib/net/rte_ip4.h
> @@ -223,21 +223,17 @@ rte_ipv4_phdr_cksum(const struct rte_ipv4_hdr *ipv4_hdr, uint64_t ol_flags)
>                 uint8_t  zero;     /* zero. */
>                 uint8_t  proto;    /* L4 protocol type. */
>                 uint16_t len;      /* L4 length. */
> -       } psd_hdr;
> -
> -       uint32_t l3_len;
> -
> -       psd_hdr.src_addr = ipv4_hdr->src_addr;
> -       psd_hdr.dst_addr = ipv4_hdr->dst_addr;
> -       psd_hdr.zero = 0;
> -       psd_hdr.proto = ipv4_hdr->next_proto_id;
> -       if (ol_flags & (RTE_MBUF_F_TX_TCP_SEG | RTE_MBUF_F_TX_UDP_SEG)) {
> -               psd_hdr.len = 0;
> -       } else {
> -               l3_len = rte_be_to_cpu_16(ipv4_hdr->total_length);
> -               psd_hdr.len = rte_cpu_to_be_16((uint16_t)(l3_len -
> -                       rte_ipv4_hdr_len(ipv4_hdr)));
> -       }
> +       } psd_hdr = {
> +               .src_addr = ipv4_hdr->src_addr,
> +               .dst_addr = ipv4_hdr->dst_addr,
> +               .proto = ipv4_hdr->next_proto_id,
> +               .len = (ol_flags & (RTE_MBUF_F_TX_TCP_SEG | RTE_MBUF_F_TX_UDP_SEG))
> +                       ? (uint16_t)0
> +                       : rte_cpu_to_be_16((uint16_t)(rte_be_to_cpu_16(ipv4_hdr->total_length) -
> +                                       rte_ipv4_hdr_len(ipv4_hdr)))
> +       };
> +       RTE_SUPPRESS_UNINITIALIZED_WARNING(psd_hdr);
> +
>         return rte_raw_cksum(&psd_hdr, sizeof(psd_hdr));
>  }
>
> diff --git a/lib/net/rte_ip6.h b/lib/net/rte_ip6.h
> index d1abf1f5d5..8a7e5e4b8a 100644
> --- a/lib/net/rte_ip6.h
> +++ b/lib/net/rte_ip6.h
> @@ -560,19 +560,18 @@ rte_ipv6_phdr_cksum(const struct rte_ipv6_hdr *ipv6_hdr, uint64_t ol_flags)
>  static inline uint16_t
>  rte_ipv6_phdr_cksum(const struct rte_ipv6_hdr *ipv6_hdr, uint64_t ol_flags)
>  {
> -       uint32_t sum;
>         struct {
>                 rte_be32_t len;   /* L4 length. */
>                 rte_be32_t proto; /* L4 protocol - top 3 bytes must be zero */
> -       } psd_hdr;
> -
> -       psd_hdr.proto = (uint32_t)(ipv6_hdr->proto << 24);
> -       if (ol_flags & (RTE_MBUF_F_TX_TCP_SEG | RTE_MBUF_F_TX_UDP_SEG))
> -               psd_hdr.len = 0;
> -       else
> -               psd_hdr.len = ipv6_hdr->payload_len;
> +       } psd_hdr = {
> +               .len = (ol_flags & (RTE_MBUF_F_TX_TCP_SEG | RTE_MBUF_F_TX_UDP_SEG))
> +                       ? (rte_be32_t)0
> +                       : ipv6_hdr->payload_len,
> +               .proto = (uint32_t)(ipv6_hdr->proto << 24)
> +       };
> +       RTE_SUPPRESS_UNINITIALIZED_WARNING(psd_hdr);
>
> -       sum = __rte_raw_cksum(&ipv6_hdr->src_addr,
> +       uint32_t sum = __rte_raw_cksum(&ipv6_hdr->src_addr,
>                 sizeof(ipv6_hdr->src_addr) + sizeof(ipv6_hdr->dst_addr),
>                 0);
>         sum = __rte_raw_cksum(&psd_hdr, sizeof(psd_hdr), sum);
> --
> 2.39.5 (Apple Git-154)
>

RE: [PATCH v11] net: optimize raw checksum computation

[Morten Brørup]

> Changes in v8:
> - __rte_raw_cksum: use native pointer arithmetic instead of RTE_PTR_ADD
>   to avoid incorrect results with -O3 for UDP checksums. Also improves
>   performance due to less assembly generated with Clang.

Personally, I also have observed GCC's optimizer behave as if it loses some contextual information when using RTE_PTR_ADD, and thus emitting less optimal code.
I didn't look further into it, and thus have no data or examples to back up the claim. Which is why I haven't started a discussion about discouraging the use of RTE_PTR_ADD.
In other words: I support this change.

>  	/* if length is odd, keeping it byte order independent */
> -	if (unlikely(len % 2)) {
> +	if (len & 1) {
>  		uint16_t left = 0;
> -
>  		memcpy(&left, end, 1);
>  		sum += left;
>  	}

Changing "len % 2" to "len & 1" made sense for consistency in previous versions handling 32/16/8/4/2-byte chunks before this 1-byte chunk; now it makes no difference, so consider not changing this part at all.
Under all circumstances, don't remove the unlikely() for handling odd length in __rte_raw_cksum(). The vast majority of packets (and partial packets, e.g. headers) being checksummed are even length.

Re: [PATCH v11] net: optimize raw checksum computation

[Scott Mitchell]

On Fri, Jan 9, 2026 at 4:26 AM Morten Brørup <mb@smartsharesystems.com> wrote:
>
> > Changes in v8:
> > - __rte_raw_cksum: use native pointer arithmetic instead of RTE_PTR_ADD
> >   to avoid incorrect results with -O3 for UDP checksums. Also improves
> >   performance due to less assembly generated with Clang.
>
> Personally, I also have observed GCC's optimizer behave as if it loses some contextual information when using RTE_PTR_ADD, and thus emitting less optimal code.
> I didn't look further into it, and thus have no data or examples to back up the claim. Which is why I haven't started a discussion about discouraging the use of RTE_PTR_ADD.
> In other words: I support this change.

Sounds good! I observed ~600 (dpdk ptr macros) vs ~500 (native c ptr
operations) TSC cycles/block in cksum_perf_autotest.

>
> >       /* if length is odd, keeping it byte order independent */
> > -     if (unlikely(len % 2)) {
> > +     if (len & 1) {
> >               uint16_t left = 0;
> > -
> >               memcpy(&left, end, 1);
> >               sum += left;
> >       }
>
> Changing "len % 2" to "len & 1" made sense for consistency in previous versions handling 32/16/8/4/2-byte chunks before this 1-byte chunk; now it makes no difference, so consider not changing this part at all.
> Under all circumstances, don't remove the unlikely() for handling odd length in __rte_raw_cksum(). The vast majority of packets (and partial packets, e.g. headers) being checksummed are even length.
>

Sounds good. I will restore the original.

The use case that motivated these changes was software interfaces (veth)
with encapsulation requiring software checksum on inner IPv4 payloads,
where lengths may be odd/even. However, I agree that header checksums
with even lengths are the more common case and unlikely() is appropriate.

RE: [PATCH v11] net: optimize raw checksum computation

[Morten Brørup]

> From: Scott Mitchell [mailto:scott.k.mitch1@gmail.com]
> Sent: Friday, 9 January 2026 16.27
> 
> On Fri, Jan 9, 2026 at 4:26 AM Morten Brørup <mb@smartsharesystems.com>
> wrote:
> >
> > > Changes in v8:
> > > - __rte_raw_cksum: use native pointer arithmetic instead of
> RTE_PTR_ADD
> > >   to avoid incorrect results with -O3 for UDP checksums. Also
> improves
> > >   performance due to less assembly generated with Clang.
> >
> > Personally, I also have observed GCC's optimizer behave as if it
> loses some contextual information when using RTE_PTR_ADD, and thus
> emitting less optimal code.
> > I didn't look further into it, and thus have no data or examples to
> back up the claim. Which is why I haven't started a discussion about
> discouraging the use of RTE_PTR_ADD.
> > In other words: I support this change.
> 
> Sounds good! I observed ~600 (dpdk ptr macros) vs ~500 (native c ptr
> operations) TSC cycles/block in cksum_perf_autotest.

That is a significant performance degradation caused by the RTE_PTR_ADD() macros. We really should look into that - some day. ;-)
Our application code base has RTE_CONST_PTR_ADD/SUB() for type consistency reasons (not for performance reasons). But I haven't gotten around to submitting them to the DPDK project yet.
I wonder if the implicit stripping of "const" when using the RTE_PTR_ADD() macros makes the difference, or if the difference stems from other optimizer context getting lost.

> 
> >
> > >       /* if length is odd, keeping it byte order independent */
> > > -     if (unlikely(len % 2)) {
> > > +     if (len & 1) {
> > >               uint16_t left = 0;
> > > -
> > >               memcpy(&left, end, 1);
> > >               sum += left;
> > >       }
> >
> > Changing "len % 2" to "len & 1" made sense for consistency in
> previous versions handling 32/16/8/4/2-byte chunks before this 1-byte
> chunk; now it makes no difference, so consider not changing this part
> at all.
> > Under all circumstances, don't remove the unlikely() for handling odd
> length in __rte_raw_cksum(). The vast majority of packets (and partial
> packets, e.g. headers) being checksummed are even length.
> >
> 
> Sounds good. I will restore the original.
> 
> The use case that motivated these changes was software interfaces
> (veth)
> with encapsulation requiring software checksum on inner IPv4 payloads,
> where lengths may be odd/even.

You might want to mention the use case in the cover letter or patch description.
Having a real use case often helps getting a patch accepted, especially for optimization patches.

> However, I agree that header checksums
> with even lengths are the more common case and unlikely() is
> appropriate.

In my experience (and based on statistics from our appliances deployed), internet traffic is dominated by "max size" (1500 byte or QUIC "safe max" somewhat below 1500 byte) packets and empty TCP ACK packets, which are even size.
So I also consider the unlikely()applicable to "real life" traffic on the internet.
Although it's not in the order of magnitude many people advocate should be a requirement for unlikely().

Re: [PATCH v11] net: optimize raw checksum computation

[Scott Mitchell]

On Fri, Jan 9, 2026 at 10:58 AM Morten Brørup <mb@smartsharesystems.com> wrote:
>
> > From: Scott Mitchell [mailto:scott.k.mitch1@gmail.com]
> > Sent: Friday, 9 January 2026 16.27
> >
> > On Fri, Jan 9, 2026 at 4:26 AM Morten Brørup <mb@smartsharesystems.com>
> > wrote:
> > >
> > > > Changes in v8:
> > > > - __rte_raw_cksum: use native pointer arithmetic instead of
> > RTE_PTR_ADD
> > > >   to avoid incorrect results with -O3 for UDP checksums. Also
> > improves
> > > >   performance due to less assembly generated with Clang.
> > >
> > > Personally, I also have observed GCC's optimizer behave as if it
> > loses some contextual information when using RTE_PTR_ADD, and thus
> > emitting less optimal code.
> > > I didn't look further into it, and thus have no data or examples to
> > back up the claim. Which is why I haven't started a discussion about
> > discouraging the use of RTE_PTR_ADD.
> > > In other words: I support this change.
> >
> > Sounds good! I observed ~600 (dpdk ptr macros) vs ~500 (native c ptr
> > operations) TSC cycles/block in cksum_perf_autotest.
>
> That is a significant performance degradation caused by the RTE_PTR_ADD() macros. We really should look into that - some day. ;-)
> Our application code base has RTE_CONST_PTR_ADD/SUB() for type consistency reasons (not for performance reasons). But I haven't gotten around to submitting them to the DPDK project yet.
> I wonder if the implicit stripping of "const" when using the RTE_PTR_ADD() macros makes the difference, or if the difference stems from other optimizer context getting lost.
>
> >
> > >
> > > >       /* if length is odd, keeping it byte order independent */
> > > > -     if (unlikely(len % 2)) {
> > > > +     if (len & 1) {
> > > >               uint16_t left = 0;
> > > > -
> > > >               memcpy(&left, end, 1);
> > > >               sum += left;
> > > >       }
> > >
> > > Changing "len % 2" to "len & 1" made sense for consistency in
> > previous versions handling 32/16/8/4/2-byte chunks before this 1-byte
> > chunk; now it makes no difference, so consider not changing this part
> > at all.
> > > Under all circumstances, don't remove the unlikely() for handling odd
> > length in __rte_raw_cksum(). The vast majority of packets (and partial
> > packets, e.g. headers) being checksummed are even length.
> > >
> >
> > Sounds good. I will restore the original.
> >
> > The use case that motivated these changes was software interfaces
> > (veth)
> > with encapsulation requiring software checksum on inner IPv4 payloads,
> > where lengths may be odd/even.
>
> You might want to mention the use case in the cover letter or patch description.
> Having a real use case often helps getting a patch accepted, especially for optimization patches.
>

Will do. Big win for this patch is enabling vectorization on clang
which doesn't require the changes to the last byte.

> > However, I agree that header checksums
> > with even lengths are the more common case and unlikely() is
> > appropriate.
>
> In my experience (and based on statistics from our appliances deployed), internet traffic is dominated by "max size" (1500 byte or QUIC "safe max" somewhat below 1500 byte) packets and empty TCP ACK packets, which are even size.
> So I also consider the unlikely()applicable to "real life" traffic on the internet.
> Although it's not in the order of magnitude many people advocate should be a requirement for unlikely().
>

1.5k internet common-case makes sense. We have use cases using jumbo frames
where non-full-frames aren't uncommon.