Jason Wang
2020-Dec-16 05:56 UTC
[PATCH net 2/2] vhost_net: fix high cpu load when sendmsg fails
----- Original Message -----> > > > -----Original Message----- > > From: Jason Wang [mailto:jasowang at redhat.com] > > Sent: Tuesday, December 15, 2020 12:10 PM > > To: wangyunjian <wangyunjian at huawei.com>; netdev at vger.kernel.org; > > mst at redhat.com; willemdebruijn.kernel at gmail.com > > Cc: virtualization at lists.linux-foundation.org; Lilijun (Jerry) > > <jerry.lilijun at huawei.com>; chenchanghu <chenchanghu at huawei.com>; > > xudingke <xudingke at huawei.com>; huangbin (J) > > <brian.huangbin at huawei.com> > > Subject: Re: [PATCH net 2/2] vhost_net: fix high cpu load when sendmsg > > fails > > > > > > On 2020/12/15 ??9:48, wangyunjian wrote: > > > From: Yunjian Wang <wangyunjian at 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. > > > > > > Signed-off-by: Yunjian Wang <wangyunjian at 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..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; > > > - } > > > > > > 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? Thanks> > Thanks > > > > > > > - 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 > > > > > Thanks > > > > > > > + 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 > >