ran manevich, leon polishuk, israel cidon, and avinoam kolodny
DESCRIPTION
Design Tradeoffs of Long Links in Hierarchical Tiled Networks-on-Chip. Ran Manevich, Leon Polishuk, Israel Cidon, and Avinoam Kolodny. . Electrical Engineering Department Technion – Israel Institute of Technology Haifa, Israel. QNoC. Research. Group. Hierarchical NoCs . PyraMesh - PowerPoint PPT PresentationTRANSCRIPT
Design Tradeoffs of Long Links in Hierarchical Tiled Networks-on-
Chip
Ran Manevich, Leon Polishuk, Israel Cidon, and Avinoam Kolodny.
Module
Modu le Module
Modu le Modu le
Modu le Modu le
Modu le
Module
Modu le
Modu le
Modu leGroup
Research
Electrical Engineering DepartmentTechnion – Israel Institute of Technology
Haifa, Israel
1
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
3
Max. Hop distance vs. Number of Modules
# of Modules
# of Modl sog ule
Go Go
Hierarchical
NoCs!!!
LONG LINKSWho is right?
4
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 sizeS repeater size normalized to hR ,C input C and output R of min size inverter
20.5 wired RCl
5
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
6
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.
7
Wire design parameters
ΛW – Scaling of W vs. min. size global wire [ITRS].
Parameter RangeΛW [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
8
Cost of adjusted links
Wiring Cost -
Power Cost -
Unified cost function -
. ,wire
Cwire
PP
P
Adjusted WireMin 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
9
Finding lowest cost wires for target frequency
Parameter RangeΛW [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.
10
Lowest cost links – 29nm-8nm technology nodes
Max. achievable single cycle
lengths – 29nm
Max. achievable single cycle
lengths – 20nm
11
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 example1 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 GHz2 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%
16
Costs of adjusting wires to 3GHz
3 GHz
Cost Function (CF) [%]<1% 6% >1% 4% 39%
17
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 wiresTotal cost of minimum size wires
Overhead
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.2
1
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!!!
23
LONG
NOT THAT LONG !
LONG
LONG
Thank You!
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