1 Link Division Multiplexing (LDM) for NoC Links IEEE 2006

LDM

Link Division MultiplexingArkadiy Morgenshtein, Avinoam Kolodny, Ran Ginosar

Technion – Israel Institute of Technology

MATRICS Research Group, Electrical Engineering DepartmentTechnion – Israel Institute of Technology

Haifa, Israel

MATRICSResearch

Group

2 Link Division Multiplexing (LDM) for NoC Links IEEE 2006

Background

&

Motivation

3 Link Division Multiplexing (LDM) for NoC Links IEEE 2006

Networks-on-Chip (NoC)

Router

Module

NoC Characteristics

• Packets-based data routing

• Modules connected by routers network

• Shared links

• Supports QoS communication - QNoC

4 Link Division Multiplexing (LDM) for NoC Links IEEE 2006

Quality of Service in NoC

QNoC – NoC with QoS

• Signaling – urgent short packets

• Read-Time – audio/video applications

• Read/Write – memory and register access

• Block-Transfer – long blocks of data

low latency, high priority

latency ↑, priority ↓

latency ↑ ↑, priority ↓ ↓

high latency, low priority

5 Link Division Multiplexing (LDM) for NoC Links IEEE 2006

Motivation

tt

• Data is transmitted using Time-Sharing

• At each time slot all the wires are dedicated to a single source

• QoS priority defines order and duration for each source

- Low link utilization

- Timing dependency

- High power

solutionLink Division Multiplexing

(LDM)

Data flow in QNoC links

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LDM Concept

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multi-serial LDM

m

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m-parallel Time Sharing

m

Link Division Multiplexing (LDM)

• Link resources (wires) are divided among QoS levels – Link Division Multiplexing

• The link is composed of outputs of several serializers

• Each serializer is dedicated to transmission of data at certain QoS level

• The number of wires at each level is allocated according to QoS level priority.

• LDM allows simultaneous transport of data in various QoS levels.

m-t

o-1

serial Time Sharing

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• LDM allows dynamic division of resources according to QoS levels

+ Full utilization of the link resources

+ No timing dependency of lower QoS levels on higher levels

+ Simultaneous data transport at different QoS levels while maintaining the

throughput and latency demands

+ Higher data transmission rate with improved efficiency of power control

Link Division Multiplexing (LDM)

X m

-to

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eria

lize

rs

m

9 Link Division Multiplexing (LDM) for NoC Links IEEE 2006

LDM Architecture

10 Link Division Multiplexing (LDM) for NoC Links IEEE 2006

LDM Transceiver

Controller

InputBuffer n1

m

Serializers

m→n

m→n

m→n

m→n

ClientsData

n2

n3

n4

n1n→m

n2

n3

n4

n→m

n→m

n→m

Deserializers

ClientsData

OutputBuffer

outin

Link

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Controller Implementation

Trade-offs

Add the control data to the packet.

Each wire carries the information about the packet to which it is designated.

+ Reduced wiring overhead

- Reduced data efficiency rate

Predefined allocation patterns of wires.

Wires allocated according to operation mode without control communication.

+ Reduced hardware overhead

- Reduced flexibility and utilization

Send control signals at dedicated wires.

Additional wires used for control communication in the transceiver.

+ High data efficiency rate & flexibility - Increased wiring overhead

Alternative

our architecture

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QNoC Router with LDM Link

SIGNAL

RT

RD/WR

BLOCK

MUX

Scheduler

Buffers

m

SIGNAL

RT

RD/WR

BLOCK

Controller

Buffer

n3

n4

n2

n1

m

m→nserializer

m→nserializer

m→nserializer

m→nserializer

TDM LDM

• TDM – data is classified and stored in dedicated buffers according to QoS levels • LDM – various QoS levels are treated simultaneously, no need for separate storage

+ Fewer buffers are needed in LDM

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Results

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Simulation Setup

• LDM communication environment was implemented and emulated in Matlab

• QNoC link with 32 wires connected between two routers with four clients each

• Two possible patterns of wires allocation were set:

• {8,8,8,8}

• {16,8,4,4}

• Four QoS levels were used – Signaling, Real-Time, R/W, Block-Transfer

• Parameters were defined for each QoS level:

• Size of packet (in 32-bit flits)

• Probability of data appearance at given QoS level (including “no data”)

• Delay expressing the processing time of packet before transmission

• For each client a profile was built basing on set of five data probabilities

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LDM in Various Data Scenarios

• Simulations contained data generation and transport during 100,000 clock cycles• The simulation scenarios were divided into two types:

• Homogeneous – same QoS probability profiles for all clients• Heterogeneous – different QoS probability profiles for all clients

• Number of transported flits in LDM was increased by up to 40%

distribution typescenarioClientQoS probabilityFlits transmitted

Pno-dataPsignalingPreal-timePread/writePblock-transLDMTDM

homogeneousAall0.300.250.050.250.159980699876

Ball0.9950.0010.0010.0010.0028998389963

heterogeneous

C

C10.10.10.20.20.4

5589039792C20.99400.0010.0050

C30.99400.0010.0050

C40.99400.0010.0050

D

C10.9930.0010.0010.0040.001

8998387572C20.990.0060.0020.0010.001

C30.30.30.050.050.3

C40.990.0010.0040.0040.001

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Performance vs. Packet Delays

TDM LDM

• LDM effectiveness was evaluated as function of packets delay before transmission. • Number of transported flits in LDM was increased by up to 50%• LDM link has maximum value for certain delay.

• for low delays there is a queue of data in the buffer• for higher delays the number of the flits reduces similarly to TDM.

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LDM with lower VDD

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TDM

Power Reduction in LDM

High link utilization in LDM

• Longer sleep mode allowed in

LDM – clock and supply gating

• Timing can be traded for Voltage

Scaling to reduce power

LDM

TTDMX

m-t

o-n

se

rial

ize

rsTLDM

or

TLDM_low

TTDM = TLDM+ Tsleep

VTDM = VLDM

sleep

TTDM = TLDM_low

VTDM > VLDM_low

PLDM < PTDM

18 Link Division Multiplexing (LDM) for NoC Links IEEE 2006

Summary

•Link Division Multiplexing proposed

•LDM targets improvement of link utilization

•Increase in data rate and reduction of power

•LDM link was implemented and simulated

•Number of transmitted flits increased by up to 50%

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Questions?

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