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Elephants and Mice

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Elephant flow detection in the vSwitch with performance isolation handled by the underlay using standard interfaces.

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Elephants and Mice

  1. 1. v Elephants and Mice vSwitch Elephant Detection and Underlay Elephant Handling Justin Pettit, Kanna Rajagopal, JR Rivers and Martin Casado 20140515
  2. 2. Of Elephants and Mice Large data transfers “elephants” can consume disproportionate network resources (buffer/queues) which causes packet drops in other traffic, greatly increasing the mean-time-to-completion (mttc) of smaller data transfers “mice”.  mice mttc disproportionately affect application mttc cumulusnetworks.com 2
  3. 3. Project Goal Evaluate the effects of predictive signaling and distributed reaction on the elephant/mice problem Detect and signal elephants via Open vSwitch React to elephants in HW via Cumulus Linux cumulusnetworks.com 3
  4. 4. Elephant Detection and Signaling  Detect via…  per flow statistics (current) • explicitly measure flow rate over time  TCP Segmentation Offload buffer size (pending) • indicates socket is sending large amount of data  Signal via IP Differentiated Services Code Point (DSCP)  carried through entire IP fabric cumulusnetworks.com 4 vswitch elephants mice nic vm vm vm vnic vnic vnic
  5. 5. Elephant Reaction - Escalating Affects Lower drop/wred threshold in a single queue  diffserv AF behavior Alternative queue on same physical port Alternative network path cumulusnetworks.com 5 ? drop-threshold queue-select alternate-path
  6. 6. Test Topology Sources  VMs connected via Open vSwitch • 10G connection to network Network Paths  1G “normal” link • easy to congest with VM traffic sources  10G “alternative” link Sink  bare metal server • 10G connection from network cumulusnetworks.com 6 1G Open vSwitch n vm vni c 10G 10G 10G vmvni c vm vni c
  7. 7. Traffic Generation and Result Measurement Generators  elephants – nuttcp • fixed time transfers, 4M window  mice – small (10ms) interval pings • mimics tcp-acks, lock release, small db transations Results  elephants • realized bandwidth, drops  mice • mean-time-to-completion, drops cumulusnetworks.com 7
  8. 8. Results – flow statistic detection & alternate queue reaction test case (120 sec period) elephant mouse Mbps drops Latency (ms) drops elephant only 941 63 N/A N/A mouse only N/A N/A 0.444 0 mouse vs elephant no detection 941 61 3.055 0 mouse vs elephant w/detection 937 1223 0.401 0 cumulusnetworks.com 8
  9. 9. Results – flow statistic detection & alternate queue reaction cumulusnetworks.com 9 0 1 2 3 4 5 6 7 8 9 10 500 550 600 650 700 750 800 850 900 950 1000 1 11 21 31 41 51 61 71 81 91 101 111 121 131 Latencyms) Bandwidth(Mbps) Time (Secs) Mice vs Elephants (Detection off) Elephant Mice
  10. 10. Results – flow statistic detection & alternate queue reaction cumulusnetworks.com 10 0 1 2 3 4 5 6 7 8 9 10 500 550 600 650 700 750 800 850 900 950 1000 1 11 21 31 41 51 61 71 81 91 101 111 121 131 Latency(ms) Bandwidth(Mbps) Time (Secs) Mice vs Elephants (Detection on, OVS timer off) Elephant Mice
  11. 11. Next Steps TSO based detection  pre-test with Linux kernel patches  retest with updated Open vSwitch from vmware Various reactions  alternate drop threshold  alternate path cumulusnetworks.com 11
  12. 12. Thank You! cumulusnetworks.com 12

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