Transcript 幻灯片 1 - University of Connecticut

Rotary Router: An Efficient Architecture
for CMP Interconnection Networks
P. Abad, V. Puente, P. Prieto, and J.Gregorio
ISCA 2007
Presenter: Zheng Guo
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Outline
Motivation
Router Architecture
Avoiding Anomalies
Performance Evaluation
Implementation Viability
Summary and Conclusions
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Motivation
 The constraints change on chip
Wide links are the norm
Local information readily available (neighbors)
Smaller packets
 Complex networks….
Chip Multiprocessors (CMP)
Consume power especially buffering schemes
Place area pressure on caches and cores
 Need simplification
How do we deal with issues like HOL blocking,
adaptive routing and arbitration across a router?
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Router Architecture
 Injection into the
ring
 Routing tag
 Avoid HOL
blocking
 Multiple rotations
 Dual-port FIFO
Buffers (DFB)
 No centralized
structures
 Crossbars
 arbitration
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Router Building Blocks:
Input Port
 FIFO buffer
and demux
 Local routing
tag computation
 Ring selection
Distance to
port
Occupancy
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Router Building Blocks:
Output Port
 Multiplexer +
buffers
Fair access
 Flow control
with neighbor
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Router Building Blocks:
Buffering Management
 Dual-port
FIFO Buffer
(DFB)
Central block
Two-pair
Read/Write
ports
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Router Building Blocks:
Buffering Management




Buffer bypass logic when output is available
Round robin arbitration
Delay comparable to Adaptive Bubble Router
Area is buffer bound: comparable/better than traditional routers
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Operations
Arbitration
Independent of the # of output ports
Local
Simple FIFO buffer and no HOL
blocking
Router complexity grows linearly in # of
ports
Low complexity adaptive routing
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Flow Control
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Flow Control
 Virtual cut through with neighbors
 Bubble flow control for injection limitation
Deadlock freedom relies on bubble flow control
 Occupation based flow control in a ring
Levels injection probability across input ports
 Misrouting
Multiple ring traversals marks packet for
misrouting
Take first available port
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Avoiding Anomalies:
Deadlock, Livelock & Starvation
 Bubble flow control ensures progress and
deadlock freedom
 Livelock with very low probability
Misrouting is randomized
Probability of bubble following cyclic paths is very
low
 Starvation is mitigated with adaptive
injection rates
Ring buffer allocation is unfair between injection
ports and router ports
Dynamically throttle injection (required bubble
count) at router ports
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Analysis of Power Consumption
 8×8 torus
 More activity in the
router increases power
consumption
 More movement time but
less execution time
 Superior latency reduces
execution time -> reduces
energy-delay product (EDP)
 Number of turns are low
 Multiple flow control
protocols smooth out the
flows
 Never travel more than one
clycle
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Overall Performance
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Summary and Conclusions
A novel architecture
Decentralized and scalable, No HOL
No virtual channels
Topology agnostic
Component complexity independent of
node degree
However, need to better understand
effect of message size, e.g., cache lines
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Thanks
Questions?
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