[dpdk-dev] [PATCH 3/4] netvsc: set lower host latency

[Stephen Hemminger <stephen@networkplumber.org>]

Tune the vmbus connection so the host scans faster. This improves
transmit performance. The host default value is 100us but setting
to 50us reduces packet loss significantly.

Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
---
 drivers/net/netvsc/hn_ethdev.c | 6 ++++++
 drivers/net/netvsc/hn_var.h    | 3 +++
 2 files changed, 9 insertions(+)

diff --git a/drivers/net/netvsc/hn_ethdev.c b/drivers/net/netvsc/hn_ethdev.c
index 78b842ba2d68..148e6a33d682 100644
--- a/drivers/net/netvsc/hn_ethdev.c
+++ b/drivers/net/netvsc/hn_ethdev.c
@@ -264,6 +264,9 @@ static int hn_subchan_configure(struct hn_data *hv,
 			return err;
 		}
 
+		rte_vmbus_set_latency(hv->vmbus, new_sc,
+				      HN_CHAN_LATENCY_NS);
+
 		retry = 0;
 		chn_index = rte_vmbus_sub_channel_index(new_sc);
 		if (chn_index == 0 || chn_index > hv->max_queues) {
@@ -629,6 +632,9 @@ eth_hn_dev_init(struct rte_eth_dev *eth_dev)
 	if (err)
 		return err;
 
+	rte_vmbus_set_latency(hv->vmbus, hv->channels[0],
+			      HN_CHAN_LATENCY_NS);
+
 	hv->primary = hn_rx_queue_alloc(hv, 0,
 					eth_dev->device->numa_node);
 
diff --git a/drivers/net/netvsc/hn_var.h b/drivers/net/netvsc/hn_var.h
index f7ff8585bc1c..b3e0a93d45df 100644
--- a/drivers/net/netvsc/hn_var.h
+++ b/drivers/net/netvsc/hn_var.h
@@ -20,6 +20,9 @@
 /* Retry interval */
 #define HN_CHAN_INTERVAL_US	100
 
+/* Host monitor interval */
+#define HN_CHAN_LATENCY_NS	50000
+
 /* Buffers need to be aligned */
 #ifndef PAGE_SIZE
 #define PAGE_SIZE 4096
-- 
2.18.0