netdev - [PATCH net 2/2] vhost_net: fix high cpu load when sendmsg fails

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Date:   Tue, 15 Dec 2020 09:48:40 +0800
From:   wangyunjian <wangyunjian@...wei.com>
To:     <netdev@...r.kernel.org>, <mst@...hat.com>, <jasowang@...hat.com>,
        <willemdebruijn.kernel@...il.com>
CC:     <virtualization@...ts.linux-foundation.org>,
        <jerry.lilijun@...wei.com>, <chenchanghu@...wei.com>,
        <xudingke@...wei.com>, <brian.huangbin@...wei.com>,
        Yunjian Wang <wangyunjian@...wei.com>
Subject: [PATCH net 2/2] vhost_net: fix high cpu load when sendmsg fails

From: Yunjian Wang <wangyunjian@...wei.com>

Currently we break the loop and wake up the vhost_worker when
sendmsg fails. When the worker wakes up again, we'll meet the
same error. This will cause high CPU load. To fix this issue,
we can skip this description by ignoring the error. When we
exceeds sndbuf, the return value of sendmsg is -EAGAIN. In
the case we don't skip the description and don't drop packet.

Signed-off-by: Yunjian Wang <wangyunjian@...wei.com>
---
 drivers/vhost/net.c | 21 +++++++++------------
 1 file changed, 9 insertions(+), 12 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index c8784dfafdd7..f966592d8900 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -827,16 +827,13 @@ static void handle_tx_copy(struct vhost_net *net, struct socket *sock)
 				msg.msg_flags &= ~MSG_MORE;
 		}
 
-		/* TODO: Check specific error and bomb out unless ENOBUFS? */
 		err = sock->ops->sendmsg(sock, &msg, len);
-		if (unlikely(err < 0)) {
+		if (unlikely(err == -EAGAIN)) {
 			vhost_discard_vq_desc(vq, 1);
 			vhost_net_enable_vq(net, vq);
 			break;
-		}
-		if (err != len)
-			pr_debug("Truncated TX packet: len %d != %zd\n",
-				 err, len);
+		} else if (unlikely(err < 0 || err != len))
+			vq_err(vq, "Fail to sending packets err : %d, len : %zd\n", err, len);
 done:
 		vq->heads[nvq->done_idx].id = cpu_to_vhost32(vq, head);
 		vq->heads[nvq->done_idx].len = 0;
@@ -922,7 +919,6 @@ static void handle_tx_zerocopy(struct vhost_net *net, struct socket *sock)
 			msg.msg_flags &= ~MSG_MORE;
 		}
 
-		/* TODO: Check specific error and bomb out unless ENOBUFS? */
 		err = sock->ops->sendmsg(sock, &msg, len);
 		if (unlikely(err < 0)) {
 			if (zcopy_used) {
@@ -931,13 +927,14 @@ static void handle_tx_zerocopy(struct vhost_net *net, struct socket *sock)
 				nvq->upend_idx = ((unsigned)nvq->upend_idx - 1)
 					% UIO_MAXIOV;
 			}
-			vhost_discard_vq_desc(vq, 1);
-			vhost_net_enable_vq(net, vq);
-			break;
+			if (err == -EAGAIN) {
+				vhost_discard_vq_desc(vq, 1);
+				vhost_net_enable_vq(net, vq);
+				break;
+			}
 		}
 		if (err != len)
-			pr_debug("Truncated TX packet: "
-				 " len %d != %zd\n", err, len);
+			vq_err(vq, "Fail to sending packets err : %d, len : %zd\n", err, len);
 		if (!zcopy_used)
 			vhost_add_used_and_signal(&net->dev, vq, head, 0);
 		else
-- 
2.23.0