On Tue, Jan 05, 2016 at 07:13:04AM +0000, Xie, Huawei wrote:

On 12/17/2015 7:18 PM, Tom Kiely wrote:

quoted

On 11/25/2015 05:32 PM, Xie, Huawei wrote:

quoted

On 11/13/2015 5:33 PM, Tom Kiely wrote:

quoted

If all rx descriptors are processed while transient
mbuf exhaustion is present, the rx ring ends up with
no available descriptors. Thus no packets are received
on that ring. Since descriptor refill is performed post
rx descriptor processing, in this case no refill is
ever subsequently performed resulting in permanent rx
traffic drop.

Signed-off-by: Tom Kiely <redacted>
---
  drivers/net/virtio/virtio_rxtx.c |    6 ++++--
  1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/net/virtio/virtio_rxtx.c

b/drivers/net/virtio/virtio_rxtx.c
index 5770fa2..a95e234 100644

--- a/drivers/net/virtio/virtio_rxtx.c
+++ b/drivers/net/virtio/virtio_rxtx.c

@@ -586,7 +586,8 @@ virtio_recv_pkts(void *rx_queue, struct rte_mbuf

**rx_pkts, uint16_t nb_pkts)
      if (likely(num > DESC_PER_CACHELINE))
          num = num - ((rxvq->vq_used_cons_idx + num) %
DESC_PER_CACHELINE);
  -    if (num == 0)
+    /* Refill free descriptors even if no pkts recvd */
+    if (num == 0 && virtqueue_full(rxvq))

Should the return condition be that no used buffers and we have avail
descs in avail ring, i.e,
     num == 0 && rxvq->vq_free_cnt != rxvq->vq_nentries

rather than
     num == 0 && rxvq->vq_free_cnt == 0

Yes we could do that but I don't see a good reason to wait until the
vq_free_cnt == vq_nentries
before attempting the refill. The existing code will attempt refill
even if only 1 packet was received
and the free count is small. To me it seems safer to extend that to
try refill even if no packet was received
but the free count is non-zero.

The existing code attempt to refill only if 1 packet was received.

If we want to refill even no packet was received, then the strict
condition should be
    num == 0 && rxvq->vq_free_cnt != rxvq->vq_nentries

The safer condition, what you want to use,  should be
    num == 0 && !virtqueue_full(...)
rather than
    num == 0 && virtqueue_full(...)

We could simplify things a bit, just remove this check, if the following
receiving code already takes care of the "num == 0" condition.

I find virtqueue_full is confusing, maybe we could change it to some
other meaningful name.

quoted

   Tom

Ping.

Tom and Huawei, what is the status of this patch? Will there be a V2?

/Bruce