Module R R RRR R RRRRR RR R R R R Access Regulation to Hot-Modules in Wormhole NoCs Isask’har...
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Transcript of Module R R RRR R RRRRR RR R R R R Access Regulation to Hot-Modules in Wormhole NoCs Isask’har...
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Access Regulation toHot-Modules in Wormhole NoCs
Isask’har (Zigi) Walter
Supervised by:Israel Cidon, Ran Ginosar and Avinoam Kolodny
Or: Hot-Modules, Cool NoCs
Technion – Israel Institute of Technology
May 2007Hot-Modules in Wormhole
NoCs 2
Hot-Modules
NoC is designed and dimensioned to meet QoS requirements- Buffer sizing, routing, router arbitration, link capacities, …
NoC designers cannot tune everything- Modules typically have limited capacity
High-demanded, bandwidth limited modules create edge bottlenecks- In SoC, often known in advance
Off-chip DRAM, on-chip special purpose processor
System performance is strongly affected- Even if the NoC has infinite bandwidth
May 2007Hot-Modules in Wormhole
NoCs 3
Hot Module (HM) in NoC Wormhole, BE NoC
At high Hot Module utilization, multiple worms “get stuck” in the network
Two problems arise:- System Performance- Source Fairness
IP(HM) In
terf
ace
May 2007Hot-Modules in Wormhole
NoCs 4
IP3Interface
IP2
Inte
rfa
ce
IP1(HM) In
terf
ace
HM is not a local problem. Traffic not destined at the HM suffers too!
Hot Module Affects the SystemProblem
#1
May 2007Hot-Modules in Wormhole
NoCs 5
Multiple locally fair decisions
Global fairness
HM
Inte
rfac
e
The limited, expensive HM resource isn’t fairly shared
Source Fairness ProblemProblem
#2
May 2007Hot-Modules in Wormhole
NoCs 6
Our Approach
Problem is not caused by the NoC- But rather by a congested end-point
Solution should address the root cause- Not the symptoms
Utilize existing NoC infrastructure
Solve both problems- Simple and efficient
May 2007Hot-Modules in Wormhole
NoCs 7
Hot Module Congestion
During congested periods, sources should not inject packets towards the HM- Will experience increased delay anyway- Better wait at the source, not in the network
Keep routers unmodified!
May 2007Hot-Modules in Wormhole
NoCs 8
IP1
Control
IP4
NoC
Interface
Interface
IP3
IP2(HM)
HM Allocation Control Basics
Inte
rfac
eA
llocati
on
Con
trolle
r
Interface
May 2007Hot-Modules in Wormhole
NoCs 9
IP1
IP4
NoC
Interface
Interface
IP3
IP2(HM)
Inte
rfac
eControl
HM Allocation Control Basics
Allocati
on
Con
trolle
r
Interface
May 2007Hot-Modules in Wormhole
NoCs 10
IP1
Control
NoCIP2
(HM)
Allocati
on
Con
trolle
r
Interface
IP3
IP4
Interface
HM Allocation Control Basics
Inte
rfac
e
Interface
May 2007Hot-Modules in Wormhole
NoCs 11
HM Control Packets
The HM Controller receives all requests and can employ any scheduling policy
Control packets are sent using a high service level- Bypassing (blocked) data packets!
Dest.
Req. C
redit
Source
Dest.
Credit
Source
Credit request packet Credit reply packet
May 2007Hot-Modules in Wormhole
NoCs 12
Input ports Output ports
BufSize
SL 0
SL 1
CR
OS
S-B
AR
Scheduler CREDITControlCREDIT
SL 2
SL 3
SL 0
SL 1
SL 2
SL 3
Multiple Priority Router
Control packets
May 2007Hot-Modules in Wormhole
NoCs 13
Enhanced Request packet The request may include additional data as
needed- payload’s priority, deadline, expiration time, etc.
Dest.
Deadline
Expiration
Priority
Req. C
redit
Source
……
Optional fields
Credit request packet
May 2007Hot-Modules in Wormhole
NoCs 14
SRC
Size
Priority
deadline
Expiration……
The HM Allocation Controller is customized according to system’s requirements
HM Allocation Controller
PendingRequests
Table
LocalArbiter
CreditRequests
CreditReplies
Requests Decoder
Reply Encoder
Optional
HM Access Controller
May 2007Hot-Modules in Wormhole
NoCs 15
Short packets are not negotiated Source’s quota is slowly self-refreshing The mechanism is turned-off when the
network is not congested Crediting modules ahead of time hides
request-grant latency- For light-load periods
Further Enhancements
May 2007Hot-Modules in Wormhole
NoCs 16
Not Classic Flow-Control
Flow-control protects destination’s buffer- A pair-wise protocol
HM access regulation protects the system- Many-to-one protocol
May 2007Hot-Modules in Wormhole
NoCs 17
Results – Synthetic scenario Hotspot traffic
- All-to-one traffic with all-to-all background traffic
High network capacity Limited hot module bandwidth HM controller arbitration: Round-robin
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RR R R
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May 2007Hot-Modules in Wormhole
NoCs 18
System Performance
Without regulation
WithRegulation
X30
X10
Average Packet Latency
May 2007Hot-Modules in Wormhole
NoCs 19
Hot vs. non-Hot Module Traffic
HM Trafficwithout regulation
Background TrafficWithout regulation
HM Trafficwith regulation
Background TrafficWith regulation
Using regulation, non-HM traffic latency is drastically reduced
X40
Average Packet Latency
May 2007Hot-Modules in Wormhole
NoCs 20
Source Fairness
Source#16no regulation
Source#5no regulation
Source#5with regulation
Source#16with regulation
2
6
1
5
3
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4
8
109 11 12
1413 15 16
R
R
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RR R R
RR R R
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May 2007Hot-Modules in Wormhole
NoCs 21
Fairness in Saturated Network
Hot-Module Utilization: 99.99% Regulated Hot-Module Utilization: 98.32%
Simulation results for a 4-by-4 system,Data packet length: 200 flitsControl packet length: 2 flits
No allocation controlWith allocation control
May 2007Hot-Modules in Wormhole
NoCs 22
MPEG-4 Decoder
Real SoC Over provisioned NoC Two hot-modules
VU AU MED CPU
RAST
SDRAM SRAM1 SRAM2 IDCT
ADSP UP SAMP
BAB RISC
25% of all traffic
22% of all traffic
SDRAM SRAM2
May 2007Hot-Modules in Wormhole
NoCs 23
Results – MPEG-4 Decoder
@80% load: X2 reduction @80% load: X8 reduction
All traffic HM/non-HM traffic breakdown
X2
X8
May 2007Hot-Modules in Wormhole
NoCs 24
The HMs are better utilized
Without regulation, the hot-modules are only 60% utilized- Traffic to one HM blocks the traffic to the other!
No allocation controlWith allocation control
1HM1 2HM1 3HM1 4HM1 9HM1 10HM1 11HM1 8HM2 10HM2 11HM2 12HM2 Total
Flows destined at HM1
Significant differences in BW!
Flows destined at
HM2
May 2007Hot-Modules in Wormhole
NoCs 25
Hot-Module Placement
May 2007Hot-Modules in Wormhole
NoCs 26
Summary Hot-modules are common in real SoCs
Hot-modules ruin system performance and are not fairly shared- Even in NoCs with infinite capacity- The network intensifies the problem- But can also provide tools for resolving it
Simple mechanism achieves dramatic improvement- Completely eliminating the HM effects
Hot-Modules, Cool NoCs!
May 2007Hot-Modules in Wormhole
NoCs 27
Thank you!
Questions?
Hot-Modules, Cool NoCs!
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