netdev - [PATCH net-next] virtio_net: exploit napi_complete

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Message-ID: <1486223361.21871.136.camel@edumazet-glaptop3.roam.corp.google.com>
Date:   Sat, 04 Feb 2017 07:49:21 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>, Jason Wang <jasowang@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Willem de Bruijn <willemb@...gle.com>
Subject: [PATCH net-next] virtio_net: exploit napi_complete_done() return
 value

From: Eric Dumazet <edumazet@...gle.com>

Since commit 364b6055738b ("net: busy-poll: return busypolling status to
drivers"), napi_complete_done() returns a boolean that can be used
by drivers to conditionally rearm interrupts.

This patch changes virtio_net to use this boolean to avoid a bit of
overhead for busy-poll users.

Jason reports about 1.1% improvement for 1 byte TCP_RR (burst 100).

Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Acked-by: Jason Wang <jasowang@...hat.com>
Cc: Michael S. Tsirkin <mst@...hat.com>
Cc: Willem de Bruijn <willemb@...gle.com>
---
 drivers/net/virtio_net.c |   11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 0382827829d90b1d25d059609bae6d1c5ad2b6d9..29982c7f6080ae99f4753052dc80ff5310f1134b 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -1012,11 +1012,12 @@ static int virtnet_poll(struct napi_struct *napi, int budget)
 	/* Out of packets? */
 	if (received < budget) {
 		r = virtqueue_enable_cb_prepare(rq->vq);
-		napi_complete_done(napi, received);
-		if (unlikely(virtqueue_poll(rq->vq, r)) &&
-		    napi_schedule_prep(napi)) {
-			virtqueue_disable_cb(rq->vq);
-			__napi_schedule(napi);
+		if (napi_complete_done(napi, received)) {
+			if (unlikely(virtqueue_poll(rq->vq, r)) &&
+			    napi_schedule_prep(napi)) {
+				virtqueue_disable_cb(rq->vq);
+				__napi_schedule(napi);
+			}
 		}
 	}