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[v3,2/5] example: l3fwd: optimize ip checksum update

Message ID 1475495356-4038-2-git-send-email-matias.elo@nokia.com
State Accepted
Commit 91df9eab8dd6ed2aeaf367575c42fe0979435431
Headers show

Commit Message

Elo, Matias (Nokia - FI/Espoo) Oct. 3, 2016, 11:49 a.m. UTC 
When decrementing TTL the IPv4 checksum can be incrementally updated.

Signed-off-by: Matias Elo <matias.elo@nokia.com>

---
 example/l3fwd/odp_l3fwd.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

-- 
2.7.4
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Patch

diff --git a/example/l3fwd/odp_l3fwd.c b/example/l3fwd/odp_l3fwd.c
index 44778b0..95c3d85 100644
--- a/example/l3fwd/odp_l3fwd.c
+++ b/example/l3fwd/odp_l3fwd.c
@@ -158,6 +158,22 @@  static void setup_fwd_db(void)
 	}
 }
 
+/**
+ * Decrement TTL and incrementally update checksum
+ *
+ * @param ip  IPv4 header
+ */
+static inline void ipv4_dec_ttl_csum_update(odph_ipv4hdr_t *ip)
+{
+	uint16_t a = ~odp_cpu_to_be_16(1 << 8);
+
+	ip->ttl--;
+	if (ip->chksum >= a)
+		ip->chksum -= a;
+	else
+		ip->chksum += odp_cpu_to_be_16(1 << 8);
+}
+
 static int l3fwd_pkt_hash(odp_packet_t pkt, int sif)
 {
 	fwd_db_entry_t *entry;
@@ -186,8 +202,7 @@  static int l3fwd_pkt_hash(odp_packet_t pkt, int sif)
 		key.dst_port = 0;
 	}
 	entry = find_fwd_db_entry(&key);
-	ip->ttl--;
-	ip->chksum = odph_ipv4_csum_update(pkt);
+	ipv4_dec_ttl_csum_update(ip);
 	eth = odp_packet_l2_ptr(pkt, NULL);
 	if (entry) {
 		eth->src = entry->src_mac;
@@ -211,8 +226,7 @@  static int l3fwd_pkt_lpm(odp_packet_t pkt, int sif)
 	int ret;
 
 	ip = odp_packet_l3_ptr(pkt, &len);
-	ip->ttl--;
-	ip->chksum = odph_ipv4_csum_update(pkt);
+	ipv4_dec_ttl_csum_update(ip);
 	eth = odp_packet_l2_ptr(pkt, NULL);
 
 	/* network byte order maybe different from host */