From: Jason Wang <jasowang@redhat.com>
To: mst@redhat.com, jasowang@redhat.com, netdev@vger.kernel.org
Cc: kvm@vger.kernel.org, virtualization@lists.linux-foundation.org,
linux-kernel@vger.kernel.org
Subject: [PATCH net V2] vhost_net: correctly check tx avail during rx busy polling
Date: Tue, 5 Sep 2017 09:22:05 +0800 [thread overview]
Message-ID: <1504574525-4711-1-git-send-email-jasowang@redhat.com> (raw)
We check tx avail through vhost_enable_notify() in the past which is
wrong since it only checks whether or not guest has filled more
available buffer since last avail idx synchronization which was just
done by vhost_vq_avail_empty() before. What we really want is checking
pending buffers in the avail ring. Fix this by calling
vhost_vq_avail_empty() instead.
This issue could be noticed by doing netperf TCP_RR benchmark as
client from guest (but not host). With this fix, TCP_RR from guest to
localhost restores from 1375.91 trans per sec to 55235.28 trans per
sec on my laptop (Intel(R) Core(TM) i7-5600U CPU @ 2.60GHz).
Fixes: 030881372460 ("vhost_net: basic polling support")
Signed-off-by: Jason Wang <jasowang@redhat.com>
---
- The patch is needed for -stable
- Changes from V1: enable vq notification when needed
---
drivers/vhost/net.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 06d0448..1c75572 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -634,8 +634,13 @@ static int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk)
preempt_enable();
- if (vhost_enable_notify(&net->dev, vq))
+ if (!vhost_vq_avail_empty(&net->dev, vq))
vhost_poll_queue(&vq->poll);
+ else if (unlikely(vhost_enable_notify(&net->dev, vq))) {
+ vhost_disable_notify(&net->dev, vq);
+ vhost_poll_queue(&vq->poll);
+ }
+
mutex_unlock(&vq->mutex);
len = peek_head_len(rvq, sk);
--
2.7.4
next reply other threads:[~2017-09-05 1:22 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-05 1:22 Jason Wang [this message]
2017-09-05 21:48 ` [PATCH net V2] vhost_net: correctly check tx avail during rx busy polling David Miller
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