module r r rrr r rrrrr rr r r r r efficient link capacity and qos design for wormhole...
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Efficient Link Capacity and QoS Design for Wormhole
Network-on-Chip
Zvika Guz, Isask’har Walter, Evgeny Bolotin, Israel Cidon, Ran Ginosar and
Avinoam Kolodny
Technion, Israel Institute of Technology
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DATE’06 NoC Capacity Allocation 2
Problem Essence
How much capacity [bits/sec] should be assigned to each link? - All flows must meet delay requirements - Minimize total resources
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DATE’06 NoC Capacity Allocation 3
Outline
Wormhole based NoC The problem of link capacity allocation Solution:
- Wormhole delay model
- Capacity allocation algorithm Design examples Summary
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DATE’06 NoC Capacity Allocation 4
Outline
Wormhole based NoC The problem of link capacity allocation Solution:
- Wormhole delay model- capacity allocation algorithm
Design examples Summary
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DATE’06 NoC Capacity Allocation 5
IP1
Inte
rfac
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IP2
Wormhole Switching
Interface
Suits on chip interconnect Small number of buffers Low latency Virtual Channels
- interleaving packets on the same link
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DATE’06 NoC Capacity Allocation 6
Wormhole Switching
Suits on chip interconnect Small number of buffers Low latency Virtual Channels
- interleaving packets on the same link
IP1
Inte
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Interface
IP3IP2Interface
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DATE’06 NoC Capacity Allocation 7
Outline
Wormhole based NoC The problem of link capacity allocation Solution:
- Wormhole delay model
- Capacity allocation algorithm Design examples Summary
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DATE’06 NoC Capacity Allocation 8
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NoC Design Flow
Define inter-module traffic
Place modules
Allocate link capacities
Verify QoS and cost
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DATE’06 NoC Capacity Allocation 9
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NoC Design Flow
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Define inter-module traffic
Place modules
Allocate link capacities
Verify QoS and cost
Too low capacity results in poor QoS Too high capacity wastes power/area
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DATE’06 NoC Capacity Allocation 10
Capacity Allocation Problem
Simulation takes too long a simulation based solution is not scalable
If no simulations are used:- How to extract flows’ delays? - How to reassign capacity?
Our solution:- Analytical model to forecast QoS- Capacity allocation algorithm that exploit the model
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DATE’06 NoC Capacity Allocation 11
Outline
Wormhole based NoC The problem of link capacity allocation Solution:
- Wormhole delay model
- Capacity allocation algorithm Design examples Summary
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DATE’06 NoC Capacity Allocation 12
Delay Analysis
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Approximate per-flow latencies Given:
- Network topology- Link capacities- Communication demands
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DATE’06 NoC Capacity Allocation 13
Because they assume:- Symmetrical communication demands - No virtual channels- Identical link capacity!
Generally, they calculate the delay of an“average flow”- A per-flow analysis is needed
Why Previous Models Do Not Apply?
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DATE’06 NoC Capacity Allocation 14
IP1
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IP2Interface
Wormhole Delay Analysis
The delivery resembles a pipeline pass
Packet transmission can be divided into two separated phases:- Path acquisition- Packet delivery
We focus on packet delivery phase
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DATE’06 NoC Capacity Allocation 15
IP1
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IP2Interface
Packet delivery time is dominated by the slowest link- Transmission rate- Link sharing
Packet Delivery Time
Low-capacity link
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DATE’06 NoC Capacity Allocation 16
IP1
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Interface Interface
IP2
Packet Delivery Time
Packet delivery time is dominated by the slowest link- Transmission rate- Link sharing
IP3
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DATE’06 NoC Capacity Allocation 17
Analysis Basics
Determines the flow’s effective bandwidth Per link
Account for interleaving
tt
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DATE’06 NoC Capacity Allocation 18
- mean time to deliver a flit of flow i over link j [sec] - capacity of link j [bits per sec] - flit length [bits/flit] - total flit injection rate of all flows sharing link j
except for flow i [flits/sec]
Single Hop Flow, no Sharing
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DATE’06 NoC Capacity Allocation 19
- mean time to deliver a flit of flow i over link j [sec] - capacity of link j [bits per sec] - flit length [bits/flit] - total flit injection rate of all flows sharing link j
except for flow i [flits/sec]
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Bandwidth used by
other flows on link j
Single Hop Flow, with Sharing
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DATE’06 NoC Capacity Allocation 20
The Convoy Effect
Consider inter-link dependencies - Wormhole backpressure - Traffic jams down the road
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Link Load
Account for all subsequent hops Basic delay
weighted by distance
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DATE’06 NoC Capacity Allocation 21
Weakest link dominates packet delivery time
Total Packet Transmission Time
- mean packet latency for flow i [sec]iT
max( | )i i i ijT m t j
Packet size[flits/packet]
Account for weakest link
=
- mean packet latency for flow i [sec]
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DATE’06 NoC Capacity Allocation 22
Outline
Wormhole based NoC The problem of link capacity allocation Solution:
- Wormhole delay model
- Capacity allocation algorithm Design examples Summary
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DATE’06 NoC Capacity Allocation 23
Greedy, iterative algorithm
Capacity Allocation Algorithm
For each src-dst pair: Use delay model to identify most sensitive link
Increase its capacity Repeat until delay requirements are met
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DATE’06 NoC Capacity Allocation 24
Outline
Wormhole based NoC The problem of link capacity allocation Solution:
- Wormhole delay model
- Capacity allocation algorithm Design examples Summary
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DATE’06 25
Capacity Allocation – Example#1
Before optimization
After optimization00
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Total capacity re
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Uniform traffic with identical requirements Uniform allocation: 74.4Gbit/sec Capacity allocation algorithm: 69Gbit/sec
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DATE’06 26
After optimization
Before optimization
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Capacity Allocation – Example#2
A SoC-like system- Heterogeneous traffic demands and delay requirements
Uniform allocation: 41.8Gbit/sec
Total capacity re
duced by
30%
Capacity allocation algorithm: 28.7Gbit/sec
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DATE’06 NoC Capacity Allocation 27
Outline
Wormhole based NoC The problem of link capacity allocation Solution:
- Wormhole delay model
- Capacity allocation algorithm Design Examples Summary
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DATE’06 NoC Capacity Allocation 28
Summary
SoCs need non uniform link capacities- Capacity allocation
Wormhole delay analysis- Heterogeneous link capacities - Heterogeneous communication demands- Multiple VCs
Greedy allocation algorithm Design examples
- NoC cost considerably reduced
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DATE’06 NoC Capacity Allocation 29
Questions?
M odule
M odule M odule
M odule M odule
M odule M odule
M odule
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QNoCResearch
GroupGroup
ResearchQNoC
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DATE’06 NoC Capacity Allocation 30
Backup
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DATE’06 NoC Capacity Allocation 31
Grid topology Packet-switched Wormhole switching Fixed path XY routing Heterogeneous link capacities Quality-of-Service
QNoC Architecture
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Router Link
E. Bolotin, I. Cidon, R. Ginosar, A. Kolodny, “QoS Architecture and Design Process for Cost-Effective Network on Chip”, Journal of Systems Architecture, 2004
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DATE’06 NoC Capacity Allocation 32
Analysis and Simulation vs. Load
No
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Del
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Utilization
Analytical model was validated using simulations- Different link capacities- Different communication
demands
Analysis Validation
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DATE’06 NoC Capacity Allocation 33
Slack Elimination
Packet Delay Slack
Sla
ck]%
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Flow