network performance isolation in data centres using … performance isolation in data centres using...
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© British Telecommunications plc
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Network Performance Isolation in Data Centres using ConEx Congestion Policing draft-briscoe-conex-policing-01 draft-briscoe-conex-data-centre-02
Bob Briscoe Chief Researcher, BT IRTF DCLC Jul 2014
Bob Briscoe’s work is part-funded by the European Community under its Seventh Framework Programme through the Trilogy 2 project (ICT-317756)
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purpose of talk
• work proposal for the data centre latency control r-g – data centre queuing delay control – designed for global scope (inter-data-centre,... Inter-net) – this talk: adds first step: intra-data centre
• without any new protocols
• started in the IETF congestion exposure (ConEx) w-g • generalised for initial deployment without ConEx
– and even without ECN end-to-end – now even without ECN on switches (in slides, not draft)
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Network Performance Isolation in Data Centres • An important problem
– isolating between tenants, or departments – virtualisation isolates CPU / memory / storage – but network and I/O system
is highly multiplexed & distributed • SDN-based (edge) capacity partitioning*
– configuration churn: nightmare at scale – poor use of capacity • edge-based weighted round robin (or WFQ) – More common – but biases towards heavy hitters (no concept of time)
bit-rate
time bit-rate
time
* every problem in computer science can be solved by not thinking
then hiding the resulting mess under a layer of abstraction
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Outline Design – First Step edge bottlenecks by capacity design
• Edge policing like Diffserv – but congestion policing (per guest)
• isolation within FIFO queue
• no config on switches
hosts switches
VM sender VM receiver congestion policer
guest OS hypervisor switching
w
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bottleneck congestion policer
foreach pkt { i = classify_user(pkt) di += wi*(tnow-ti) //fill ti = tnow di -= s * p //drain if (di<0) {drop(pkt)}
} s: packet size p: drop prob of AQM
• in a well-provisioned link, policer rarely intervenes • but whenever needed, it limits queue growth
network policer
incoming packet stream
meter
w1 w2 wi
… di(t)
ci congestion
token bucket
Y
FIFO buffer
p(t)
AQM
…
outgoing packet stream
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wi
di(t)
ci
kwi
C
AQM
p(t)
policer
main congestion token bucket
meter
congestion burst limiter
police if either bucket empties
actually each bucket needs to be two buckets to limit bursts of congestion
• similar code – except 2 token buckets
...
if (di1<0 || di2<0) {drop(pkt)}
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performance isolation outcome
• WRR or WFQ
• congestion policer – with unequal traffic loads
• congestion policer – treats equal traffic loads
equivalently to WRR
time
rate
time
rate
time
rate
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Outline Design edge and core queue control • Edge policing like Diffserv
– but congestion policing (per-guest) • Hose model • intra-class isolation in all FIFO queues
• FIFO ECN marking on L3 switches • no other config on switches
hosts switches
VM sender VM receiver TEP / congestion policer TEP / audit
guest OS hypervisor switching
w
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trusted path congestion feedback
• Initial deployment – all under control of infrastructure admin
• ECN on guest hosts: optional – ECN enabled across tunnel
• ConEx on guest hosts: optional – any ConEx-enabled packet
doesn’t require tunnel feedback
• details – see spare slide or draft infrastructure
policer
transport sender
transport receiver
TEP TEP feedback between tunnel endpoints
Non-ConEx packets
infrastructure
policer audit
transport sender
transport receiver
ConEx packets
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Features of Solution
• Network performance isolation between tenants • No loss of LAN-like multiplexing benefits
• work-conserving • Zero (tenant-related) switch configuration • No change to existing switch implementations • Weighted performance differentiation • Simplest possible contract
• per-tenant network-wide allowance • tenant can freely move VMs around without changing allowance • sender constraint, but with transferable allowance
• Transport-Agnostic • Extensible to wide-area and inter-data-centre interconnect
Network Performance Isolation in Data Centres using congestion policing draft-briscoe-conex-policing-01 draft-briscoe-conex-data-centre-02
Q&A & spare slides
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measuring contribution to congestion = bytes weighted by congestion level = bytes dropped (or ECN-marked) = ‘congestion-volume’ as simple to measure as volume
bit-rate
time
congestion
time
10GB
0.01% congestion
1MB
1% congestion
1MB
300MB 100MB
3MB
1%
0.01%
unilateral deployment technique for data centre operator
• for e2e transports that don’t support ECN, the operator can: 1. at encap: alter 00 to 10 in outer 2. at interior buffers: turn on ECN
• defers any drops until egress • audit just before egress
can see packets to be dropped 14
• exploits: • widespread edge-edge tunnels in multi-tenant DCs to isolate forwarding • a side-effect of standard tunnelling (IP-in-IP or any ECN link encap)
DS
ECN
ingress egress
DS
ECN
DS
ECN
DS
ECN
DS
ECN
DS
ECN
E
congested network element
DS
ECN
DS
ECN
E
1 2
00 → 10
10 → 11
11 → drop
A
audit A
pol- icer
• for e2e transports that don’t support ConEx, the operator can create its own trusted feedback: 3. at decap: only for Not-ConEx
packets, feedback aggregate congestion marking counters:
• CE outer, Not-ECT inner = loss • CE outer, ECT inner = ECN
exporter collector IPFIX
meter 3
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