Re: [PATCH net v2 2/2] vhost_net: fix high cpu load when sendmsg fails
From: "Michael S. Tsirkin" <mst@redhat.com>
Date: 2020-12-16 09:24:58
Also in:
netdev
On Wed, Dec 16, 2020 at 04:20:37PM +0800, wangyunjian wrote:
From: Yunjian Wang <redacted> 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?
quoted hunk
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..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.
if (!zcopy_used) vhost_add_used_and_signal(&net->dev, vq, head, 0); else -- 2.23.0
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