[dpdk-dev] [RFC] l2fwd: trying to expose eth_igb_xmit_pkts unusual behavior

[Ciprian Barbu <ciprian.barbu@linaro.org>]

From: Ciprian Barbu <ciprian.barbu@enea.com>

This tries to show an approximate behavior described in an earlier discussion
called "can eth_igb_xmit_pkts called with len 0 affect transmission?"

I'm using Intel i350 dual port 1Gb card and I've tweaked the pool size to the
minimum possible. But unmodified l2fwd still worked withouth a sweat. After
applying this patch transmission stopped after maybe 30 seconds. Lowering the
'magic' number causes l2fwd to stop sending packets even earlier.
Using gdb I could see eth_igb_xmit_pkts always returning because nb_tx was 0
and E1000_TXD_STAT_DD was not set (approx igb_rxtx.c : 476)

Signed-off-by: Ciprian Barbu <ciprian.barbu@enea.com>
---
 examples/l2fwd/main.c | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/examples/l2fwd/main.c b/examples/l2fwd/main.c
index 17621ee..623b836 100644
--- a/examples/l2fwd/main.c
+++ b/examples/l2fwd/main.c
@@ -72,7 +72,7 @@
 #define RTE_LOGTYPE_L2FWD RTE_LOGTYPE_USER1
 
 #define MBUF_SIZE (2048 + sizeof(struct rte_mbuf) + RTE_PKTMBUF_HEADROOM)
-#define NB_MBUF   8192
+#define NB_MBUF   1024
 
 #define MAX_PKT_BURST 32
 #define BURST_TX_DRAIN_US 100 /* TX drain every ~100us */
@@ -260,7 +260,7 @@ l2fwd_main_loop(void)
 	struct rte_mbuf *m;
 	unsigned lcore_id;
 	uint64_t prev_tsc, diff_tsc, cur_tsc, timer_tsc;
-	unsigned i, j, portid, nb_rx;
+	unsigned i, j, portid, nb_rx, magic = 0;
 	struct lcore_queue_conf *qconf;
 	const uint64_t drain_tsc = (rte_get_tsc_hz() + US_PER_S - 1) / US_PER_S * BURST_TX_DRAIN_US;
 
@@ -285,6 +285,15 @@ l2fwd_main_loop(void)
 	}
 
 	while (1) {
+		if (++magic == 50000) {
+			magic = 0;
+			l2fwd_send_burst(&lcore_queue_conf[lcore_id],
+					 0,
+					 (uint8_t) 0);
+			l2fwd_send_burst(&lcore_queue_conf[lcore_id],
+					 0,
+					 (uint8_t) 1);
+		}
 
 		cur_tsc = rte_rdtsc();
 
-- 
1.9.1