A Dynamic Link Allocation Router€¦ · A Dynamic Link Allocation Router Wei Song, Doug Edwards Advanced Processor Group The University of Manchester . Advanced Processor Group 2014/5/13

2014/5/13 Advanced Processor Group

The School of Computer Science

A Dynamic Link Allocation Router

Wei Song, Doug Edwards

Advanced Processor Group

The University of Manchester



Overview

• Network-on-a-Reconfigurable-Chip

• The Dynamic Link Allocation Flow control

method

• The Dynamic Link Allocation Router

(DyLAR)

• Conclusion



The NoRC Platform

Network

Interface

Router

Processor

• NoRC: network on a

reconfigurable chip

• Running multimedia

applications

• Connection oriented

• Stochastic routing algorithm

• GALS: fully asynchronous

routers linked by CHAIN



Connection Oriented Routing

• Flit Definitions

Master Slave

Tim

e

Request to reserve a path

OK ACK

Data transmissionsData transmissionsData transmissionsData transmissionsData transmissionsData transmissions

False ACK

Data transmissions (end)


False Ack

data request content flit type flit header

data flit type flit header

Request Flit

Other Flits



The High Retry Rate

0 100 200 300 400

0

2000

4000

6000

8000

10000

12000

14000

16000

Avera

ge F

ram

e L

ate

ncy (

ns)

Frame Injection Rate (kfps)

Simulation results of a 6x6 NoC with 12 functions in network.

0 100 200 300 400

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Loss R

ate

Frame Injection Rate (kfps)

Flit Level Loss Rate

Frame Level Retry rate

7%

Virtual Channels are required to reduce to retry rate.



Overview


• The Dynamic Link Allocation Flow

control method


(DyLAR)

• Conclusion



Major Design Targets

• Implement some kind of virtual channels

• Increase the bandwidth of CHAIN links

• Reduce the area and power of the router



Increase the bandwidth C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C

C C

C

C C

C

DI00

DI01

DI10

DI11

DI20

DI21

DI30

DI31

DO00

DO01

DO10

DO11

DO20

DO21

DO30

DO31

ACKI ACKO

Dual-rail 0

Dual-rail 1

Dual-rail 2

Dual-rail 3

Asynchronous Links work better with the lower wire count.



Increase the bandwidth

A B C



Increase the bandwidth

A B C

A B C

Spatial division multiplex (SDM) is a good choice for

asynchronous NoCs.



Problems of SDM

SDM has the low bandwidth efficiency.

Master Slave

Tim

e


OK ACK

Data transmissionsData transmissionsData transmissionsData transmissionsData transmissionsData transmissions

False ACK

Data transmissions (end)


False Ack

N1 N2 N3

Spare sub-link



Problems of SDM

N1 N2 N3

N1 N2 N3



Dynamic Link Allocation

• Divide the sub-link allocation apart from

the path reservation

• Allocate idle sub-link to active

communications that reserved this link

• All communications fairly compete for the

bandwidth



Overview



method


(DyLAR)

• Conclusion



Dynamic Link Allocation Router (DyLAR)

Tran

Control

Tran

Control

Tran

Control

Arbiter

Output Buffer

Output Buffer

Output Buffer

Data

Switch

Request

Switch

Input Buffer

Input Buffer

Input Buffer

DyLAR

Router



Path Reservation Stage

Tran

Control

Tran

Control

Tran

Control

Arbiter

1

2

3

4



Data Transmission Stage

Tran

Control

Tran

Control

Tran

Control

Arbiter



Head-of-line (HOL) Problem

00 01 02 03

10 11 12 13

20 21 22 23

30 31 32 33

00 01 02 03

10 11 12 13

20 21 22 23

30 31 32 33



Backpressure

tran

_ctl

tran

_ctl

data switch

request

switch

arbiter

tran

_ctl

tran

_ctl

data switch

request

switch

arbiter



Backpressure

tran

_ctl

tran

_ctl

data switch

request

switch

arbiter

tran

_ctl

tran

_ctl

data switch

request

switch

arbiter



Overview



method


(DyLAR)

• Conclusion



Pros and Cons (comp. to SDM)

• Advantages

– Smaller latency under zero load

– Larger overall throughput under heavy load

– Smaller retry rate (smaller power consumption)

• Disadvantages

– An extra request switch in each router

– Extra control logic

– Increase the latency to pass a router



Thank You!

Questions?

Documents

A Dynamic Link Allocation Router€¦ · A Dynamic Link Allocation Router Wei Song, Doug Edwards Advanced Processor Group The University of Manchester . Advanced Processor Group 2014/5/13