[dpdk-dev] [PATCH] hash: optimize the softrss computation

[Yangchao Zhou]

Use rte_bsf32 and fast bit unset operation to optimize the softrss computation.
The following measurements shows improvement over the default
softrss computation function.

tuple lens old(cycles) new(cycles)
    3        1225         337
    9        3743         992

Signed-off-by: Yangchao Zhou <zhouyates at gmail.com>
---
 lib/librte_hash/rte_thash.h | 22 ++++++++++------------
 1 file changed, 10 insertions(+), 12 deletions(-)

diff --git a/lib/librte_hash/rte_thash.h b/lib/librte_hash/rte_thash.h
index 2fffd61..4fa5e07 100644
--- a/lib/librte_hash/rte_thash.h
+++ b/lib/librte_hash/rte_thash.h
@@ -207,15 +207,14 @@ static inline uint32_t
 rte_softrss(uint32_t *input_tuple, uint32_t input_len,
 		const uint8_t *rss_key)
 {
-	uint32_t i, j, ret = 0;
+	uint32_t i, j, map, ret = 0;
 
 	for (j = 0; j < input_len; j++) {
-		for (i = 0; i < 32; i++) {
-			if (input_tuple[j] & (1 << (31 - i))) {
-				ret ^= rte_cpu_to_be_32(((const uint32_t *)rss_key)[j]) << i |
+		for (map = input_tuple[j]; map;	map &= (map - 1)) {
+			i = rte_bsf32(map);
+			ret ^= rte_cpu_to_be_32(((const uint32_t *)rss_key)[j]) << (31 - i) |
 					(uint32_t)((uint64_t)(rte_cpu_to_be_32(((const uint32_t *)rss_key)[j + 1])) >>
-					(32 - i));
-			}
+					(i + 1));
 		}
 	}
 	return ret;
@@ -238,14 +237,13 @@ static inline uint32_t
 rte_softrss_be(uint32_t *input_tuple, uint32_t input_len,
 		const uint8_t *rss_key)
 {
-	uint32_t i, j, ret = 0;
+	uint32_t i, j, map, ret = 0;
 
 	for (j = 0; j < input_len; j++) {
-		for (i = 0; i < 32; i++) {
-			if (input_tuple[j] & (1 << (31 - i))) {
-				ret ^= ((const uint32_t *)rss_key)[j] << i |
-					(uint32_t)((uint64_t)(((const uint32_t *)rss_key)[j + 1]) >> (32 - i));
-			}
+		for (map = input_tuple[j]; map;	map &= (map - 1)) {
+			i = rte_bsf32(map);
+			ret ^= ((const uint32_t *)rss_key)[j] << (31 - i) |
+				(uint32_t)((uint64_t)(((const uint32_t *)rss_key)[j + 1]) >> (i + 1));
 		}
 	}
 	return ret;
-- 
2.7.4