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Déjà Vu Switching for Multiplane NoCs NOCS’12 University of Pittsburgh Ahmed Abousamra Rami MelhemAlex Jones.

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Presentation on theme: "Déjà Vu Switching for Multiplane NoCs NOCS’12 University of Pittsburgh Ahmed Abousamra Rami MelhemAlex Jones."— Presentation transcript:

1 Déjà Vu Switching for Multiplane NoCs NOCS’12 University of Pittsburgh Ahmed Abousamra Rami MelhemAlex Jones

2 Déjà Vu Switching for Multiplane NoCs NOCS’12 Power efficiency has become a primary concern in the design of CMPs. The NoC of Intel’s TeraFLOPS processor consumes more than 28% of the chip’s power. Network messages can be classified into critical and non-critical It may be possible to send non-critical messages on a slower plane without hurting performance.

3 Déjà Vu Switching for Multiplane NoCs NOCS’12 Baseline Single Plane NoC Control Plane Data Plane Carries control and coherence messages: data requests, invalidates, acknowledgments, … Operates at baseline’s voltage & frequency Carries data messages Operates at a lower voltage & frequency to save power

4 Déjà Vu Switching for Multiplane NoCs NOCS’12 Motivation & Related work Importance of data messages to performance The Optimization Problem Proposed Solution Déjà Vu Switching Analysis of the acceptable data plane speed Evaluation Summary

5 Déjà Vu Switching for Multiplane NoCs NOCS’12 1 1 2 2 3 3 4 4 5 5 6 6 7 7 8 8 Cache line having 8 data words Data Message 5 5 1 1 2 2 3 3 4 4 6 6 7 7 8 8 Header Critical Word Subsequent miss for another word in the line  Delayed cache hit Critical Word Non-Critical Words

6 Déjà Vu Switching for Multiplane NoCs NOCS’12 If delayed cache hits are overly delayed, performance can suffer. Percentage of L1 misses that are delayed cache hits

7 Déjà Vu Switching for Multiplane NoCs NOCS’12 Motivation & Related work Importance of data messages to performance The Optimization Problem Proposed Solution Déjà Vu Switching Analysis of the acceptable data plane speed Evaluation Summary

8 Déjà Vu Switching for Multiplane NoCs NOCS’12 How slow can we operate the data plane to maximize energy savings while not impacting performance?

9 Déjà Vu Switching for Multiplane NoCs NOCS’12 Split NoC physically into 2 planes: control + data On data plane: Use circuit-switching to speed-up communication. Reduce voltage & frequency. Send a control message to establish the circuit once a cache hit is detected. Do not block circuit establishment message: Déjà Vu Switching Analyze acceptable slow down of the data plane to minimize energy while maintaining performance.

10 Déjà Vu Switching for Multiplane NoCs NOCS’12 Request PacketReservation Packet Data Packet Control Plane Data Plane 1) Upon a cache miss, a data request is sent

11 Déjà Vu Switching for Multiplane NoCs NOCS’12 Request PacketReservation Packet Data Packet Control Plane Data Plane 2) Upon a data hit in the next cache level, the circuit reservation packet is sent

12 Déjà Vu Switching for Multiplane NoCs NOCS’12 Request PacketReservation Packet Data Packet Control Plane Data Plane 3) Finally, the data packet is sent to the requester on the reserved circuit

13 Déjà Vu Switching for Multiplane NoCs NOCS’12 231 231 Control Plane Data Plane Reserved Circuits Reservation Packets Data Packets East-North West-NorthWest-East Router

14 Déjà Vu Switching for Multiplane NoCs NOCS’12 Reservation Queue of West Input Port Reservation Queue of East Output Port Reserving the West-East Connection: EW Head of the Queues Port Names: North West South East Local

15 Déjà Vu Switching for Multiplane NoCs NOCS’12 S S Reservation Queues of the Input Ports Reservation Queues of the Output Ports E N N N N S W North West South East Local E W N Head of the Queues North West South East Local Port Names: North West South East Local

16 Déjà Vu Switching for Multiplane NoCs NOCS’12 Reservation Queues of the Input Ports Reservation Queues of the Output Ports N S North West South East Local E W N Head of the Queues North West South East Local N Port Names: North West South East Local

17 Déjà Vu Switching for Multiplane NoCs NOCS’12 Reservation Queues of the Input Ports Reservation Queues of the Output Ports N S North West South East Local E W N Port Names: North West South East Local Head of the Queues North West South East Local N

18 Déjà Vu Switching for Multiplane NoCs NOCS’12 Each input and output port must independently track the reserved circuits it is part of. Any two reservation packets that share part of their paths, must traverse all the shared links in the same order Data packets must be injected onto the data plane in the same order their reservation packets are injected onto the control plane.

19 Déjà Vu Switching for Multiplane NoCs NOCS’12 Motivation & Related work Importance of data messages to performance The Optimization Problem Proposed Solution Déjà Vu Switching Analysis of the acceptable data plane speed Evaluation Summary

20 Déjà Vu Switching for Multiplane NoCs NOCS’12 82345679121011113 Time Reservation Packet injected early at cycle 1 Data Packet injected at cycle 3

21 Déjà Vu Switching for Multiplane NoCs NOCS’12 82345679121011113 Time Reservation Packet injected early at cycle 1 Data Packet injected at cycle 3

22 Déjà Vu Switching for Multiplane NoCs NOCS’12

23 Motivation & Related work Importance of data messages to performance The Optimization Problem Proposed Solution Déjà Vu Switching Analysis of the acceptable data plane speed Evaluation Summary

24 Déjà Vu Switching for Multiplane NoCs NOCS’12 We use the functional simulator, Simics, to simulate cache coherent CMPs of 16 and 64 cores. We use Orion2 to get power numbers for the interconnect routers We evaluate with Synthetic traces: allows varying the network load Execution driven simulation of parallel benchmarks from the SPLASH-2 and PARSEC suits Interconnect Topology: Mesh

25 Déjà Vu Switching for Multiplane NoCs NOCS’12 Baseline NoC: Single plane, 16 byte links, packet switched with 3 cycles router pipeline, clocked at 4 GHz Evaluated NoC: Control plane: 6 byte links, packet switched, 4GHz Data plane: 10 byte links, circuit switched. Control and Coherence Packets: 1-flit Data Packets: Baseline NoC: 5 flits Data Plane: 7 flits

26 Déjà Vu Switching for Multiplane NoCs NOCS’12 Normalized NoC energy and completion time of synthetic traces on a 64-core CMP *Each request receives a reply data packet

27 Déjà Vu Switching for Multiplane NoCs NOCS’12 Normalized execution time on a 16-core CMP

28 Déjà Vu Switching for Multiplane NoCs NOCS’12 Normalized NoC energy on a 16-core CMP

29 Déjà Vu Switching for Multiplane NoCs NOCS’12 Normalized NoC energy and execution time on a 64-core CMP

30 Déjà Vu Switching for Multiplane NoCs NOCS’12 Performance relative to CMP with a single plane NoC on a 16-core CMP

31 Déjà Vu Switching for Multiplane NoCs NOCS’12 L. Cheng et al. (ISCA'06) and A. Flores et al. (IEEE Trans. Computers'10): Heterogeneous NoC using wires of different latency and power characteristics to improve performance and reduce NoC energy. Proposal requires wide links (75 bytes), but performance degrades with narrow links. Our work differs in: Tying latency of messages to performance Using Déjà Vu Switching to Compensate for slower data plane

32 Déjà Vu Switching for Multiplane NoCs NOCS’12 Problem: Saving power in the NoC by reducing the data plane’s power consumption without impacting performance. Delayed cache hits are important to performance. Operating data plane in circuit-switched mode allows it to operate at reduced frequency. Déjà Vu Switching allows reservation to proceed when resources are not currently available. The constraints governing the speed of the data plane can be estimated analytically.

33 Déjà Vu Switching for Multiplane NoCs NOCS’12

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