Design Tradeoffs of Long Links in Hierarchical Tiled Networks-on-Chip Group Research 1 QNoC.
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Design Tradeoffs of Long Links in Hierarchical Tiled Networks-on-Chip Ran Manevich, Leon Polishuk, Israel Cidon, and Avinoam Kolodny. M odule M odule M odule M odule M odule M odule M odule M odule M odule M odule M odule M odule Group Research Electrical Engineering Department Technion – Israel Institute of Technology Haifa, Israel 1 QNoC
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Transcript of Design Tradeoffs of Long Links in Hierarchical Tiled Networks-on-Chip Group Research 1 QNoC.
Design Tradeoffs of Long Links in Hierarchical Tiled Networks-on-
Chip
Ran Manevich, Leon Polishuk, Israel Cidon, and Avinoam Kolodny.
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Research
Electrical Engineering DepartmentTechnion – Israel Institute of Technology
Haifa, Israel
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QNoC
Hierarchical NoCs
Hybrid Ring/Mesh S. Bourduas and, Z. Zilic, “Latency reduction of global traffic in wormhole-routed meshes using hierarchical rings for global routing.” ASAP 2007.
PyraMesh R. Manevich, I Cidon and, A. Kolodny. “Handling global
traffic in future CMP NoCs” SLIP 2012.
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Hierarchical NoCs lower hop distances
2D Mesh
14 Hops
PyraMesh
10 Hops
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Max. Hop distance vs. Number of Modules
# of Modules
# of Modl sog ule
Go Go
Hierarchical
NoCs!!!
LONG LINKSWho is right?
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Parallel link delay model
Elmore’s delay:
20.5wired RCl
[ / mm] [F/ mm], [ ],R C l mm
Repeated wire [Bakoglu - 1990]:
0
, 0 00.7 0.4 0.7wire repeated R R
R
R C R Cd l hS C hS C
hS
R
0 0
[repeaters / mm], h Bakoglu 's optimal repeater size
S repeater size normalized to h
R ,C input C and output R of min size inverter
20.5 wired RCl
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Links delay in 16x16 hierarchical NoC
300 mm2 die
Short1 mm
Medium1.9 mm
Long3.4 mm
16x16 Mesh. 8x8, 4x4 Upper Levels
Elmore’s Delay – Unrepeated, min. size global links (ITRS):
29 nm Technology
Short: 0.11nsMedium: 0.41nsLong: 1.31ns
12X
~17mm
LONG LINKS
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Adjusting delay of parallel links
Wire sizing: Lower RC delay by changing wire pitch (S and W).
Repeaters insertion: Lower wire delay by inserting repeaters.
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Wire design parameters
ΛW – Scaling of W vs. min. size global wire [ITRS].
Parameter Range
ΛW [1..50]
ΛS [1..50]
ρ [0..10]
SR [0..1]
ΛS – Scaling of S vs. min. size global wire
ρ - Density of repeaters per millimeter
SR – Repeaters’ size normalized to Bakolu’s optimal size
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Cost of adjusted links
Wiring Cost -
Power Cost -
Unified cost function -
. ,wire
Cwire
PP
P
Adjusted Wire
Min Global Wire ITRS
C CCF W P 1, , 0
. ,C
Pitch
Pitch
Adjusted WireW
Min Global Wire ITRS
WC = 1 WC = 2
Min. Pitc
h
2X Min. Pitch
WE USE0.5
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Finding lowest cost wires for target frequency
Parameter Range
ΛW [1..50]
ΛS [1..50]
ρ [0..10]
SR [0..1]
1. Shuffle multiple design configurations (Monte-Carlo).
2. For the target frequency, place each configuration on “Cost Function (CF)-Link Length” plane.
3. Lowest cost configurations along the Pareto curve.
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Lowest cost links – 29nm-8nm technology nodes
Max. achievable single cycle
lengths – 29nm
Max. achievable single cycle
lengths – 20nm
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Max. achievable link length for different target
frequencies
3.4 mm
Hierarchical NoCs with single-cycle long links are
feasible at practical frequencies – it’s all a matter of cost. 1
2
Back to our example
1 mm 1.9 mm 3.4 mm
29nm, 17nm, 10nm Technology nodes
1 GHz – 5GHz Target frequencies.
Delay of wires at:
Cost of adjusting wires to:
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Our example – Delays of NoC wires before
adjustements
1 GHz
2 GHz
5 GHz3 GHz
4 GHz
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Costs of adjusting wires to 1GHz
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<1%
Cost Function (CF) [%]
1 GHz
Costs of adjusting wires to 2GHz
2 GHz
Cost Function (CF) [%]<1% 11%
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Costs of adjusting wires to 3GHz
3 GHz
Cost Function (CF) [%]<1% 6% >1% 4% 39%
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Costs of adjusting wires to 4GHz
4 GHz
Cost Function (CF) [%]>1% 19% 84%>1% 1% 19%>1% 3%
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Costs of adjusting wires to 5GHz
5 GHz
Cost Function (CF) [%]1% 36% 164
%>1% 4% 39%>1% 6%1%
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Definition of cost overhead of adjusting long wires
In our example (CF = Cost Function, l = length ):
Total cost of adjusted wires
Total cost of minimum size wiresOverhead
long – 3.4mmmed – 1.9mmshort – 1mm
( ) ( ) ( ) ( ) ( ) ( )
( ) ( ) ( )
CF short l short CF med l med CF long l long
l short l med l long
Overhead
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Total length of each kind of links – our 16x16 NoC
Hierarchical NoCs - Few long wires -
Low overhead of adjusting them not to be a bottleneck.21
Cost overhead of adjusting long wires – our 16x16 NoC
65 nm28 nm
28 nm 22
Conclusions
• Long links in hierarchical NoCs: Are a minority. Are not that long! LONGER ≠ LONG Can be adjusted for single cycle at practical
target frequencies with low system costs.
Multi-cycle
long links
Single-cycle long
links
LONG LINKS
Go Go
Hierarchi
cal
NoCs!!!
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LONG
NOT THAT LONG !
LONG
LONG
Thank You!
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