This document discusses experiments on detecting and handling "elephant" traffic flows that use disproportionate network resources. It tested using Open vSwitch to detect large flows via per-flow statistics and signaling them using DSCP. Cumulus Linux then reacted by lowering drop thresholds or steering flows to alternate queues/paths. Results showed detecting elephants allowed mice flows to complete faster with few drops, while elephants achieved similar bandwidth. Next steps include refining detection and testing different reaction methods.
What Are The Drone Anti-jamming Systems Technology?
Elephants and Mice
1. v
Elephants and Mice
vSwitch Elephant Detection and Underlay Elephant
Handling
Justin Pettit, Kanna Rajagopal, JR Rivers and Martin Casado
20140515
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
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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
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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
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vswitch
elephants
mice
nic
vm
vm
vm
vnic
vnic
vnic
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
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?
drop-threshold
queue-select
alternate-path
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
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1G
Open vSwitch
n
vm
vni
c
10G
10G
10G
vmvni
c
vm
vni
c
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
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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
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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
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