Under low rate traffic conditions, there can be 2 issues.
  (1) Packets potentially can get stuck in the intermediate queue.
  (2) Latency of the packets can increase significantly due to
       buffering in intermediate queue.

This commit handles the (1) issue by flushing the tx port queues from
PMD processing loop. Also this commit addresses issue (2) by flushing
the tx queues after every rxq port processing. This reduces the latency
with out impacting the forwarding throughput.

   MASTER
  --------
   Pkt size  min(ns)   avg(ns)   max(ns)
    512      4,631      5,022    309,914
   1024      5,545      5,749    104,294
   1280      5,978      6,159     45,306
   1518      6,419      6,774    946,850

  MASTER + COMMIT
  -----------------
   Pkt size  min(ns)   avg(ns)   max(ns)
    512      4,711      5,064    182,477
   1024      5,601      5,888    701,654
   1280      6,018      6,491    533,037
   1518      6,467      6,734    312,471

PMDs can be teared down and spawned at runtime and so the rxq and txq
mapping of the PMD threads can change. In few cases packets can get
stuck in the queue due to reconfiguration and this commit helps flush
the queues.

Suggested-by: Eelco Chaudron <echau...@redhat.com>
Reported-at: 
https://mail.openvswitch.org/pipermail/ovs-dev/2017-April/331039.html
Signed-off-by: Bhanuprakash Bodireddy <bhanuprakash.bodire...@intel.com>
Signed-off-by: Antonio Fischetti <antonio.fische...@intel.com>
Co-authored-by: Antonio Fischetti <antonio.fische...@intel.com>
Signed-off-by: Markus Magnusson <markus.magnus...@ericsson.com>
Co-authored-by: Markus Magnusson <markus.magnus...@ericsson.com>
Acked-by: Eelco Chaudron <echau...@redhat.com>
---
 lib/dpif-netdev.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
index d59208e..dfd88aa 100644
--- a/lib/dpif-netdev.c
+++ b/lib/dpif-netdev.c
@@ -3761,6 +3761,8 @@ reload:
         for (i = 0; i < poll_cnt; i++) {
             dp_netdev_process_rxq_port(pmd, poll_list[i].rx,
                                        poll_list[i].port_no);
+
+            dp_netdev_flush_txq_ports(pmd);
         }
 
         if (lc++ > 1024) {
@@ -3781,6 +3783,9 @@ reload:
         }
     }
 
+    /* Flush the queues as part of reconfiguration logic. */
+    dp_netdev_flush_txq_ports(pmd);
+
     poll_cnt = pmd_load_queues_and_ports(pmd, &poll_list);
     exiting = latch_is_set(&pmd->exit_latch);
     /* Signal here to make sure the pmd finishes
-- 
2.4.11

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