6.3. 解決方法

次の例は、core_ids が dpdk0 に固定されている PMD にサービスを提供し、管理トラフィックのみが dpdk0 を流れるシステムを示しています。

[root@overcloud-compute-0 ~]# ovs-appctl dpif-netdev/pmd-stats-clear && sleep 10 && ovs-appctl dpif-netdev/pmd-stats-show |
egrep 'core_id (2|22):' -A9
pmd thread numa_id 0 core_id 22:
    emc hits:0
    megaflow hits:0
    avg. subtable lookups per hit:0.00
    miss:0
    lost:0
    polling cycles:12613298746 (100.00%)
    processing cycles:0 (0.00%)
--
pmd thread numa_id 0 core_id 2:
    emc hits:5
    megaflow hits:0
    avg. subtable lookups per hit:0.00
    miss:0
    lost:0
    polling cycles:12480023709 (100.00%)
    processing cycles:14354 (0.00%)
    avg cycles per packet: 2496007612.60 (12480038063/5)
    avg processing cycles per packet: 2870.80 (14354/5)

次の例は、core_ids が dpdk0 に固定されている PMD にサービスを提供し、負荷テストが dpdk0 を通過して、多数の RX ドロップを引き起こすシステムを示しています。

[root@overcloud-compute-0 ~]# ovs-appctl dpif-netdev/pmd-stats-clear && sleep 10 && ovs-appctl dpif-netdev/pmd-stats-show |
egrep 'core_id (2|4|22|24):' -A9
pmd thread numa_id 0 core_id 22:
    emc hits:35497952
    megaflow hits:0
    avg. subtable lookups per hit:0.00
    miss:0
    lost:0
    polling cycles:1446658819 (6.61%)
    processing cycles:20453874401 (93.39%)
    avg cycles per packet: 616.95 (21900533220/35497952)
    avg processing cycles per packet: 576.20 (20453874401/35497952)
--
pmd thread numa_id 0 core_id 2:
    emc hits:30183582
    megaflow hits:0
    avg. subtable lookups per hit:0.00
    miss:2
    lost:0
    polling cycles:1497174615 (6.85%)
    processing cycles:20354613261 (93.15%)
    avg cycles per packet: 723.96 (21851787876/30183584)
    avg processing cycles per packet: 674.36 (20354613261/30183584)

パケットドロップが発生する場合、処理サイクルとポーリングサイクルの比率が高いことがわかります (90% 以上の処理サイクル)。

polling cycles:1497174615 (6.85%)
processing cycles:20354613261 (93.15%)

パケットあたりの平均サイクル (CPP) とパケットあたりの平均処理サイクル (PCPP) を確認します。アイドルサイクルはカウントされないため、完全にロードされた PMD の PCPP/CPP 比は 1 と予想できます。

avg cycles per packet: 723.96 (21851787876/30183584)
avg processing cycles per packet: 674.36 (20354613261/30183584)

次の例は、core_ids が dpdk0 に固定された PMD にサービスを提供し、負荷テストが dpdk0 を通過して、この dpdk0 インターフェイス (約 12.85 Mpps) の 6.4 Mpps (最大容量の約 50%) を送信するシステムを示しています。

[root@overcloud-compute-0 ~]# ovs-appctl dpif-netdev/pmd-stats-clear && sleep 10 && ovs-appctl dpif-netdev/pmd-stats-show |
egrep 'core_id (2|4|22|24):' -A9
pmd thread numa_id 0 core_id 22:
    emc hits:17461158
    megaflow hits:0
    avg. subtable lookups per hit:0.00
    miss:0
    lost:0
    polling cycles:4948219259 (25.81%)
    processing cycles:14220835107 (74.19%)
    avg cycles per packet: 1097.81 (19169054366/17461158)
    avg processing cycles per packet: 814.43 (14220835107/17461158)
--
pmd thread numa_id 0 core_id 2:
    emc hits:14874381
    megaflow hits:0
    avg. subtable lookups per hit:0.00
    miss:0
    lost:0
    polling cycles:5460724802 (29.10%)
    processing cycles:13305794333 (70.90%)
    avg cycles per packet: 1261.67 (18766519135/14874381)
    avg processing cycles per packet: 894.54 (13305794333/14874381)

pps がインターフェイスの最大値の約半分である場合、処理サイクルとポーリングサイクルの比率が低くなります (約 70% の処理サイクル)。

polling cycles:5460724802 (29.10%)
processing cycles:13305794333 (70.90%)

次の例は、対象に関する man ページを示しています。

an ovs-vswitchd
(...)
   DPIF-NETDEV COMMANDS
       These commands are used to expose  internal  information  (mostly  statistics)
       about  the  `dpif-netdev`  userspace datapath. If there is only one datapath
       (as is often the case, unless dpctl/ commands are used), the dp  argument  can
       be omitted.

       dpif-netdev/pmd-stats-show [dp]
              Shows  performance  statistics  for each pmd thread of the datapath dp.
              The special thread ``main'' sums up the statistics  of  every  non  pmd
              thread.   The  sum of ``emc hits'', ``masked hits'' and ``miss'' is the
              number of packets received by the datapath.  Cycles are  counted  using
              the  TSC  or  similar  facilities when available on the platform.  To
              reset these counters use dpif-netdev/pmd-stats-clear. The  duration  of
              one cycle depends on the measuring infrastructure.
(...)

Raw

man ovs-dpctl
(...)
       dump-dps
              Prints the name of each configured datapath on a separate line.

       [-s | --statistics] show [dp...]
              Prints  a summary of configured datapaths, including their datapath numbers and a list of ports connected to each datapath.  (The local port is
              identified as port 0.)  If -s or --statistics is specified, then packet and byte counters are also printed for each port.

              The datapath numbers consists of flow stats and mega flow mask stats.

              The "lookups" row displays three stats related to flow lookup triggered by processing incoming packets in the datapath. "hit"  displays  number
              of  packets  matches  existing flows. "missed" displays the number of packets not matching any existing flow and require user space processing.
              "lost" displays number of packets destined for user space process but subsequently dropped before reaching userspace.  The  sum  of  "hit"  and
              "miss" equals to the total number of packets datapath processed.
(...)

Raw

man ovs-vswitchd
(...)
       dpctl/show [-s | --statistics] [dp...]
              Prints a summary of configured datapaths, including their datapath numbers and a list of ports connected to each datapath.  (The local port is  identified  as
              port 0.)  If -s or --statistics is specified, then packet and byte counters are also printed for each port.

              The datapath numbers consists of flow stats and mega flow mask stats.

              The  "lookups"  row  displays  three  stats  related to flow lookup triggered by processing incoming packets in the datapath. "hit" displays number of packets
              matches existing flows. "missed" displays the number of packets not matching any existing flow and require user space processing.  "lost" displays  number  of
              packets  destined for user space process but subsequently dropped before reaching userspace. The sum of "hit" and "miss" equals to the total number of packets
              datapath processed.
(...)