----- Original Message -----

quoted

-----Original Message-----
From: Jason Wang [mailto:jasowang@redhat.com]
Sent: Wednesday, December 16, 2020 1:57 PM
To: wangyunjian <redacted>
Cc: netdev@vger.kernel.org; mst@redhat.com; willemdebruijn kernel
[off-list ref];
virtualization@lists.linux-foundation.org;
Lilijun (Jerry) [off-list ref]; chenchanghu
[off-list ref]; xudingke [off-list ref]; huangbin (J)
[off-list ref]
Subject: Re: [PATCH net 2/2] vhost_net: fix high cpu load when sendmsg
fails



----- Original Message -----

quoted

quoted

-----Original Message-----
From: Jason Wang [mailto:jasowang@redhat.com]
Sent: Tuesday, December 15, 2020 12:10 PM
To: wangyunjian <redacted>; netdev@vger.kernel.org;
mst@redhat.com; willemdebruijn.kernel@gmail.com
Cc: virtualization@lists.linux-foundation.org; Lilijun (Jerry)
[off-list ref]; chenchanghu [off-list ref];
xudingke [off-list ref]; huangbin (J)
[off-list ref]
Subject: Re: [PATCH net 2/2] vhost_net: fix high cpu load when sendmsg
fails


On 2020/12/15 上午9:48, wangyunjian wrote:

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From: Yunjian Wang <redacted>

Currently we break the loop and wake up the vhost_worker when

sendmsg

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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 <redacted>
---
  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,

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struct socket *sock)

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  				msg.msg_flags &= ~MSG_MORE;
  		}

-		/* TODO: Check specific error and bomb out unless ENOBUFS?

*/

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  		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;
-		}

As I've pointed out in last version. If you don't discard descriptor,
you
probably
need to add the head to used ring. Otherwise this descriptor will be
always
inflight that may confuse drivers.

Sorry for missing the comment.

After deleting discard descriptor and break, the next processing will be
the
same
as the normal success of sendmsg(), and vhost_zerocopy_signal_used() or
vhost_add_used_and_signal() method will be called to add the head to used
ring.

It's the next head not the one that contains the buggy packet?

In the modified code logic, the head added to used ring is exectly the
one that contains the buggy packet.

-ENOTEA :( You're right, I misread the code.

Thanks

Thanks

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Thanks

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Thanks

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-		if (err != len)
-			pr_debug("Truncated TX packet: len %d != %zd\n",
-				 err, len);
+		} else if (unlikely(err < 0 || err != len))

It looks to me err != len covers err < 0.

OK

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Thanks

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+			vq_err(vq, "Fail to sending packets err : %d, len : %zd\n",

err,

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+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)

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  			msg.msg_flags &= ~MSG_MORE;
  		}

-		/* TODO: Check specific error and bomb out unless ENOBUFS?

*/

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  		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

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*net, struct socket *sock)

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  				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,

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+len);
  		if (!zcopy_used)
  			vhost_add_used_and_signal(&net->dev, vq, head, 0);
  		else