trafgen: Pre-calculate checksums if possible

The TCP/UDP checksums cannot be calculated in the parser as the packet
payload following the TCP/UDP header is not yet know. However, we can
calculate these checksums before the send loop if the only dynamic
elements of the packet are checksums.

This change avoids the overhead of recalculating the checksums for every
iteration the send loop in these cases.

Suggested-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Tobias Klauser <tklauser@distanz.ch>

1 files changed, 19 insertions, 0 deletions

diff --git a/trafgen.c b/trafgen.c
index c35182e..8752255 100644
--- a/trafgen.c
+++ b/trafgen.c
@@ -366,6 +366,21 @@ static void apply_csum16(int id)
 	}
 }
 
+static void preprocess_packets(void)
+{
+	size_t i;
+
+	for (i = 0; i < plen; i++) {
+		struct packet_dyn *pktd = &packet_dyn[i];
+
+		if (packet_dyn_has_only_csums(pktd)) {
+			apply_csum16(i);
+			pktd->slen = 0;
+			xfree(pktd->csum);
+		}
+	}
+}
+
 static struct cpu_stats *setup_shared_var(unsigned int cpus)
 {
 	int fd;
@@ -539,6 +554,8 @@ static void xmit_slowpath_or_die(struct ctx *ctx, unsigned int cpu, unsigned lon
 
 	drop_privileges(ctx->enforce, ctx->uid, ctx->gid);
 
+	preprocess_packets();
+
 	bug_on(gettimeofday(&start, NULL));
 
 	while (likely(sigint == 0 && num > 0 && plen > 0)) {
@@ -628,6 +645,8 @@ static void xmit_fastpath_or_die(struct ctx *ctx, unsigned int cpu, unsigned lon
 	if (ctx->num == 0 && orig_num > 0)
 		num = 0;
 
+	preprocess_packets();
+
 	bug_on(gettimeofday(&start, NULL));
 
 	while (likely(sigint == 0 && num > 0 && plen > 0)) {