[ovs-dev] [PATCH v3 6/6] dpif-netdev: Flush the packets in intermediate queue.

[Darrell Ball]

-----Original Message-----
From: <ovs-dev-bounces at openvswitch.org> on behalf of Bhanuprakash Bodireddy <bhanuprakash.bodireddy at intel.com>
Date: Thursday, June 29, 2017 at 3:39 PM
To: "dev at openvswitch.org" <dev at openvswitch.org>
Subject: [ovs-dev] [PATCH v3 6/6] dpif-netdev: Flush the packets in	intermediate queue.

    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 <echaudro at redhat.com>
    Reported-at: https://urldefense.proofpoint.com/v2/url?u=https-3A__mail.openvswitch.org_pipermail_ovs-2Ddev_2017-2DApril_331039.html&d=DwICAg&c=uilaK90D4TOVoH58JNXRgQ&r=BVhFA09CGX7JQ5Ih-uZnsw&m=bHrBe9xQ4KZyIP8eXmMQgmAki-7TrHqH1PHcy7KBp9M&s=FLHjFbETDpuejnwNxIJem8vPtHo7KDb0q0YJSIpsMb8&e= 
    Signed-off-by: Bhanuprakash Bodireddy <bhanuprakash.bodireddy at intel.com>
    Signed-off-by: Antonio Fischetti <antonio.fischetti at intel.com>
    Co-authored-by: Antonio Fischetti <antonio.fischetti at intel.com>
    Signed-off-by: Markus Magnusson <markus.magnusson at ericsson.com>
    Co-authored-by: Markus Magnusson <markus.magnusson at ericsson.com>
    Acked-by: Eelco Chaudron <echaudro at redhat.com>
    ---
     lib/dpif-netdev.c | 7 +++++++
     1 file changed, 7 insertions(+)
    
    diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
    index 7e1f5bc..f03bd3e 100644
    --- a/lib/dpif-netdev.c
    +++ b/lib/dpif-netdev.c
    @@ -3603,6 +3603,8 @@ dpif_netdev_run(struct dpif *dpif)
                     for (i = 0; i < port->n_rxq; i++) {
                         dp_netdev_process_rxq_port(non_pmd, port->rxqs[i].rx,
                                                    port->port_no);
    +
    +                    dp_netdev_flush_txq_ports(non_pmd);



Is this a temporary change ?; seems counter to the objective ?
Should be latency based, as discussed on another thread couple months ago ?; configurable by port type and port ?



                     }
                 }
             }
    @@ -3760,6 +3762,8 @@ 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);
             }



Same comment as above.


     
             if (lc++ > 1024) {
    @@ -3780,6 +3784,9 @@ 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
    
    _______________________________________________
    dev mailing list
    dev at openvswitch.org
    https://urldefense.proofpoint.com/v2/url?u=https-3A__mail.openvswitch.org_mailman_listinfo_ovs-2Ddev&d=DwICAg&c=uilaK90D4TOVoH58JNXRgQ&r=BVhFA09CGX7JQ5Ih-uZnsw&m=bHrBe9xQ4KZyIP8eXmMQgmAki-7TrHqH1PHcy7KBp9M&s=9f249RikCnGphA_CpKIFbbtkbo2W6axBPaub91khHeM&e=