Re: [PATCH 2/2] vhost-net: revert vhost_exceeds_maxpend logic to its original

[Jason Wang]

On 2017年08月19日 14:41, Koichiro Den wrote:

To depend on vq.num and the usage of VHOST_MAX_PEND is not succinct
and in some case unexpected, so revert its logic part only.

Hi:

Could you explain a little bit more on the case that is was not sufficent?

Thanks

Signed-off-by: Koichiro Den <d...@klaipeden.com>
---
  drivers/vhost/net.c | 8 ++++++--
  1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 06d044862e58..99cf99b308a7 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -433,11 +433,15 @@ static int vhost_net_tx_get_vq_desc(struct vhost_net *net,

static bool vhost_exceeds_maxpend(struct vhost_net *net)

  {
+       int num_pends;
        struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX];
        struct vhost_virtqueue *vq = &nvq->vq;

- return (nvq->upend_idx + vq->num - VHOST_MAX_PEND) % UIO_MAXIOV

-               == nvq->done_idx;
+       num_pends = likely(nvq->upend_idx >= nvq->done_idx) ?
+               (nvq->upend_idx - nvq->done_idx) :
+               (nvq->upend_idx + UIO_MAXIOV - nvq->done_idx);
+
+       return num_pends > VHOST_MAX_PEND;
  }

/* Expects to be always run from workqueue - which acts as