From: stephen hemminger <stephen@networkplumber.org>
Date: Fri, 28 Jul 2017 08:59:47 -0700
Patch-mainline: v4.14-rc1
Subject: netvsc: signal host if receive ring is emptied
Git-commit: f4e403633bcd290a4db2568364657d07b42ff890
References: fate#323887

Latency improvement related to NAPI conversion.
If all packets are processed from receive ring then need
to signal host.

Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Olaf Hering <ohering@suse.de>
---
 drivers/net/hyperv/netvsc.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/net/hyperv/netvsc.c b/drivers/net/hyperv/netvsc.c
--- a/drivers/net/hyperv/netvsc.c
+++ b/drivers/net/hyperv/netvsc.c
@@ -1195,10 +1195,15 @@ int netvsc_poll(struct napi_struct *napi, int budget)
 		nvchan->desc = hv_pkt_iter_next(channel, nvchan->desc);
 	}
 
-	/* If send of  pending receive completions suceeded
-	 *   and did not exhaust NAPI budget
+	/* if ring is empty, signal host */
+	if (!nvchan->desc)
+		hv_pkt_iter_close(channel);
+
+	/* If send of pending receive completions suceeded
+	 *   and did not exhaust NAPI budget this time
 	 *   and not doing busy poll
-	 * then reschedule if more data has arrived from host
+	 * then re-enable host interrupts
+	 *     and reschedule if ring is not empty.
 	 */
 	if (send_recv_completions(nvchan) == 0 &&
 	    work_done < budget &&