[dpdk-dev] [PATCH v2 3/4] hash: add fallback to software CRC32 implementation

[Yerden Zhumabekov]

Initially, SSE4.2 support is detected via CPUID instruction.

Added rte_hash_crc_set_alg() function to detect and set CRC32
implementation if necessary. SSE4.2 is allowed by default. If it's
not available, fall back to sw implementation.

Signed-off-by: Yerden Zhumabekov <e_zhumabekov at sts.kz>
---
 lib/librte_hash/rte_hash_crc.h |   60 ++++++++++++++++++++++++++++++++++++++--
 1 file changed, 58 insertions(+), 2 deletions(-)

diff --git a/lib/librte_hash/rte_hash_crc.h b/lib/librte_hash/rte_hash_crc.h
index 74e2d92..178b162 100644
--- a/lib/librte_hash/rte_hash_crc.h
+++ b/lib/librte_hash/rte_hash_crc.h
@@ -45,7 +45,11 @@ extern "C" {
 #endif
 
 #include <stdint.h>
+#ifdef RTE_MACHINE_CPUFLAG_SSE4_2
 #include <nmmintrin.h>
+#endif
+#include <rte_cpuflags.h>
+#include <rte_branch_prediction.h>
 
 /* Lookup table for software implementation of CRC32C */
 static const uint32_t crc32c_table[256] = {
@@ -152,8 +156,42 @@ crc32c_2words(uint64_t data, uint32_t init_val)
 	return init_val;
 }
 
+enum crc32_alg_t {
+	CRC32_SW = 0,
+	CRC32_SSE42,
+	CRC32_AUTODETECT
+};
+
+/* Default algorithm is left for autodetection,
+ * it is detected on first run of hash function
+ */
+static enum crc32_alg_t crc32_alg = CRC32_AUTODETECT;
+
+/**
+ * Allow or disallow use of SSE4.2 instrinsics for CRC32 hash
+ * hash calculation.
+ *
+ * @param flag
+ *   unsigned integer flag
+ *   - (CRC32_SW) Don't use SSE4.2 intrinsics
+ *   - (CRC32_SSE42) Use SSE4.2 intrinsics if available, set by default
+ */
+static inline void
+rte_hash_crc_set_alg(enum crc32_alg_t alg)
+{
+	int sse42_supp = rte_cpu_get_flag_enabled(RTE_CPUFLAG_SSE4_2);
+	enum crc32_alg_t alg_supp = sse42_supp ? CRC32_SSE42 : CRC32_SW;
+
+	if (alg == CRC32_SSE42)
+		crc32_alg = alg_supp;
+	else
+		crc32_alg = CRC32_SW;
+}
+
 /**
  * Use single crc32 instruction to perform a hash on a 4 byte value.
+ * Fall back to software crc32 implementation in case SSE4.2 is
+ * not supported
  *
  * @param data
  *   Data to perform hash on.
@@ -165,11 +203,21 @@ crc32c_2words(uint64_t data, uint32_t init_val)
 static inline uint32_t
 rte_hash_crc_4byte(uint32_t data, uint32_t init_val)
 {
-	return _mm_crc32_u32(init_val, data);
+	if (unlikely(crc32_alg == CRC32_AUTODETECT))
+		rte_hash_crc_set_alg(CRC32_SSE42);
+
+#ifdef RTE_MACHINE_CPUFLAG_SSE4_2
+	if (likely(crc32_alg == CRC32_SSE42))
+		return _mm_crc32_u32(init_val, data);
+#endif
+
+	return crc32c_1word(data, init_val);
 }
 
 /**
  * Use single crc32 instruction to perform a hash on a 8 byte value.
+ * Fall back to software crc32 implementation in case SSE4.2 is
+ * not supported
  *
  * @param data
  *   Data to perform hash on.
@@ -181,7 +229,15 @@ rte_hash_crc_4byte(uint32_t data, uint32_t init_val)
 static inline uint32_t
 rte_hash_crc_8byte(uint64_t data, uint32_t init_val)
 {
-	return _mm_crc32_u64(init_val, data);
+	if (unlikely(crc32_alg == CRC32_AUTODETECT))
+		rte_hash_crc_set_alg(CRC32_SSE42);
+
+#ifdef RTE_MACHINE_CPUFLAG_SSE4_2
+	if (likely(crc32_alg == CRC32_SSE42))
+		return _mm_crc32_u64(init_val, data);
+#endif
+
+	return crc32c_2words(data, init_val);
 }
 
 /**
-- 
1.7.9.5