> -----Original Message-----
> From: Michael S. Tsirkin [mailto:m...@redhat.com]
> Sent: Wednesday, December 16, 2020 5:23 PM
> To: wangyunjian <wangyunj...@huawei.com>
> Cc: netdev@vger.kernel.org; jasow...@redhat.com;
> willemdebruijn.ker...@gmail.com; virtualizat...@lists.linux-foundation.org;
> Lilijun (Jerry) <jerry.lili...@huawei.com>; chenchanghu
> <chenchan...@huawei.com>; xudingke <xudin...@huawei.com>; huangbin (J)
> <brian.huang...@huawei.com>
> Subject: Re: [PATCH net v2 2/2] vhost_net: fix high cpu load when sendmsg
> fails
>
> On Wed, Dec 16, 2020 at 04:20:37PM +0800, wangyunjian wrote:
> > From: Yunjian Wang <wangyunj...@huawei.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.
>
> Question: with this patch, what happens if sendmsg is interrupted by a signal?
The descriptors are consumed as normal. However, the packet is discarded.
Could you explain the specific scenario?
>
>
> >
> > Signed-off-by: Yunjian Wang <wangyunj...@huawei.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..3d33f3183abe 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 != 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);
>
> I'd rather make the pr_debug -> vq_err a separate change, with proper commit
> log describing motivation.
This log was originally triggered when packets were truncated. But after the
modification of this patch, other error scenarios will also trigger this log.
That's why I modified the content and level of this log together.
Now, should I just change the content of this patch?
Thanks
>
>
> > if (!zcopy_used)
> > vhost_add_used_and_signal(&net->dev, vq, head, 0);
> > else
> > --
> > 2.23.0
