Re: [dpdk-dev, v3] Implement memcmp using Intel SIMD instrinsics.

[...]

+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * Compare bytes between two locations. The locations must not overlap.
+ *

Parameter names should be kept consistent as they are in function body.

+ * @param src_1
+ *   Pointer to the first source of the data.
+ * @param src_2
+ *   Pointer to the second source of the data.
+ * @param n
+ *   Number of bytes to compare.
+ * @return
+ *   zero if src_1 equal src_2
+ *   -ve if src_1 less than src_2
+ *   +ve if src_1 greater than src_2
+ */
+static inline int
+rte_memcmp(const void *src_1, const void *src,
+		size_t n) __attribute__((always_inline));
+
+/**
+ * Find the first different bit for comparison.
+ */
+static inline int
+rte_cmpffd (uint32_t x, uint32_t y)
+{
+	int i;
+	int pos = x ^ y;
+	for (i = 0; i < 32; i++)
+		if (pos & (1<<i))

Coding style check :-)
BTW, does the bsf instruction provide this check?

+			return i;
+	return -1;
+}
+

[...]

+/**
+ * Compare 48 bytes between two locations.
+ * Locations should not overlap.
+ */
+static inline int
+rte_cmp48(const void *src_1, const void *src_2)

Guess this is not used.

[...]

+/**
+ * Compare 256 bytes between two locations.
+ * Locations should not overlap.
+ */
+static inline int
+rte_cmp256(const void *src_1, const void *src_2)
+{
+	int ret;
+
+	ret = rte_cmp64((const uint8_t *)src_1 + 0 * 64,
+			(const uint8_t *)src_2 + 0 * 64);

Why not just use rte_cmp128?


[...]

+static inline int
+rte_memcmp(const void *_src_1, const void *_src_2, size_t n)
+{
+	const uint8_t *src_1 = (const uint8_t *)_src_1;
+	const uint8_t *src_2 = (const uint8_t *)_src_2;
+	int ret = 0;
+
+	if (n < 16)
+		return rte_memcmp_regular(src_1, src_2, n);
+
+	if (n <= 32) {
+		ret = rte_cmp16(src_1, src_2);
+		if (unlikely(ret != 0))
+			return ret;
+
+		return rte_cmp16(src_1 - 16 + n, src_2 - 16 + n);
+	}
+

Too many conditions here may harm the overall performance.
It's a trade-off thing, all about balancing the overhead.
Just make sure this is tuned based on actual test numbers.

+	if (n <= 48) {
+		ret = rte_cmp32(src_1, src_2);
+		if (unlikely(ret != 0))
+			return ret;
+
+		return rte_cmp16(src_1 - 16 + n, src_2 - 16 + n);
+	}
+
+	if (n <= 64) {
+		ret = rte_cmp32(src_1, src_2);
+		if (unlikely(ret != 0))
+			return ret;
+
+		ret = rte_cmp16(src_1 + 32, src_2 + 32);
+
+		if (unlikely(ret != 0))
+			return ret;
+
+		return rte_cmp16(src_1 - 16 + n, src_2 - 16 + n);
+	}
+
+	if (n <= 96) {
+		ret = rte_cmp64(src_1, src_2);
+		if (unlikely(ret != 0))
+			return ret;
+
+		ret = rte_cmp16(src_1 + 64, src_2 + 64);
+		if (unlikely(ret != 0))
+			return ret;
+
+		return rte_cmp16(src_1 - 16 + n, src_2 - 16 + n);
+	}
+
+	if (n <= 128) {
+		ret = rte_cmp64(src_1, src_2);
+		if (unlikely(ret != 0))
+			return ret;
+
+		ret = rte_cmp32(src_1 + 64, src_2 + 64);
+		if (unlikely(ret != 0))
+			return ret;
+
+		ret = rte_cmp16(src_1 + 96, src_2 + 96);
+		if (unlikely(ret != 0))
+			return ret;
+
+		return rte_cmp16(src_1 - 16 + n, src_2 - 16 + n);
+	}

[...]

+/**
+ * Compare 48 bytes between two locations.
+ * Locations should not overlap.
+ */
+static inline int
+rte_cmp48(const void *src_1, const void *src_2)

Not used.

+{
+	int ret;
+
+	ret = rte_cmp16((const uint8_t *)src_1 + 0 * 16,
+			(const uint8_t *)src_2 + 0 * 16);
+
+	if (unlikely(ret != 0))
+		return ret;
+
+	ret = rte_cmp16((const uint8_t *)src_1 + 1 * 16,
+			(const uint8_t *)src_2 + 1 * 16);
+
+	if (unlikely(ret != 0))
+		return ret;
+
+	return rte_cmp16((const uint8_t *)src_1 + 2 * 16,
+			(const uint8_t *)src_2 + 2 * 16);
+}
+
+/**
+ * Compare 64 bytes between two locations.
+ * Locations should not overlap.
+ */
+static inline int
+rte_cmp64(const void *src_1, const void *src_2)
+{
+	int ret;
+
+	ret = rte_cmp16((const uint8_t *)src_1 + 0 * 16,
+			(const uint8_t *)src_2 + 0 * 16);

Why not rte_cmp32? And use rte_cmp64 for rte_cmp128, and so on.
That should make the code looks clearer.


It'd be great if you could format this patch into a patch set with several
little ones. :-)
Also, the kernel checkpatch is very helpful.
Good coding style and patch organization make it easy for in-depth reviews.