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Download Access Regulation to Hot-Modules in Wormhole NoCs
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R R Module R Module R Module Access Regulation to R R Module Hot-Modules in Wormhole NoCs Module Module R R R R R Or: Hot-Modules, NoCsModule Module Module Cool Module Module R R R Isask’har (Zigi) Walter Module R R Module R Supervised by: Module Israel Cidon, Ran Ginosar and Avinoam Kolodny Module Technion – Israel Institute of Technology 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 2007 Hot-Modules in Wormhole NoCs 2 Hot Module (HM) in NoC Wormhole, BE NoC IP At high Hot Module utilization, multiple worms “get stuck” in the network (HM) Interface Two problems arise: - System Performance - Source Fairness May 2007 Hot-Modules in Wormhole NoCs 3 (HM) IP2 Interface IP1 Interface Hot Module Affects the System Interface IP3 HM is not a local problem. Traffic not destined at the HM suffers too! May 2007 Hot-Modules in Wormhole NoCs 4 Multiple locally fair decisions HM Interface Source Fairness Problem Global fairness The limited, expensive HM resource isn’t fairly shared May 2007 Hot-Modules in Wormhole NoCs 5 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 2007 Hot-Modules in Wormhole NoCs 6 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 2007 Hot-Modules in Wormhole NoCs 7 HM Allocation Control Basics IP3 Interface IP2 (HM) Interface Allocation Controller Control IP1 NoC Interface Interface IP4 May 2007 Hot-Modules in Wormhole NoCs 8 HM Allocation Control Basics IP3 Interface IP2 (HM) Interface Allocation Controller Control IP1 NoC Interface Interface IP4 May 2007 Hot-Modules in Wormhole NoCs 9 HM Allocation Control Basics IP3 Interface IP2 (HM) Interface Allocation Controller Control IP1 NoC Interface Interface IP4 May 2007 Hot-Modules in Wormhole NoCs 10 HM Control Packets Credit Source Dest. Req. Credit Source Dest. Credit request packet Credit reply packet 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! May 2007 Hot-Modules in Wormhole NoCs 11 Multiple Priority Router Control packets Input ports Output ports BufSize SL 0 SL 1 SL 1 SL 2 SL 2 SL 3 CREDIT May 2007 Control CROSS-BAR SL 0 SL 3 Scheduler Hot-Modules in Wormhole NoCs CREDIT 12 Enhanced Request packet The request may include additional data as needed - payload’s priority, deadline, expiration time, etc. Optional fields … … Deadline Expiration Priority Req. Credit Source Dest. Credit request packet May 2007 Hot-Modules in Wormhole NoCs 13 HM Allocation Controller The HM Allocation Controller is customized according to system’s requirements Credit Requests Optional SRC Size Priority deadline Expiration … … Pending Requests Table Requests Decoder Credit Replies Reply Encoder Local Arbiter HM Access Controller May 2007 Hot-Modules in Wormhole NoCs 14 Further Enhancements 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 May 2007 Hot-Modules in Wormhole NoCs 15 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 2007 Hot-Modules in Wormhole NoCs 16 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 R HM R Module R Module R R May 2007 Hot-Modules in Wormhole NoCs R Module R Module R Module Module Module Module R R R R Module Module Module Module R R Module R Module R Module 17 System Performance Average Packet Latency Without regulation X30 X10 May 2007 Hot-Modules in Wormhole NoCs With Regulation 18 Hot vs. non-Hot Module Traffic Average Packet Latency Background Traffic Without regulation HM Traffic without regulation X40 HM Traffic with regulation Background Traffic With regulation Using regulation, non-HM traffic latency is drastically reduced May 2007 Hot-Modules in Wormhole NoCs 19 Source Fairness Source#16 no regulation Source#16 with regulation Source#5 with regulation 1 5 R R 6 R R R 3 7 R R R 4 8 R Source#5 no regulation R R 10 11 12 R R R R 13 14 15 16 9 R 2 May 2007 Hot-Modules in Wormhole NoCs 20 Fairness in Saturated Network No allocation control With allocation control Simulation results for a 4-by-4 system, Data packet length: 200 flits Control packet length: 2 flits May 2007 Hot-Module Utilization: 99.99% Regulated Hot-Module Utilization: 98.32% Hot-Modules in Wormhole NoCs 21 MPEG-4 Decoder Real SoC Over provisioned NoC Two hot-modules 22% of all traffic VU AU MED CPU RAST SDRAM SRAM1 SRAM2 IDCT ADSP UP SAMP BAB RISC 25% of all traffic May 2007 Hot-Modules in Wormhole NoCs 22 Results – MPEG-4 Decoder All traffic HM/non-HM traffic breakdown X8 X2 @80% load: X2 reduction May 2007 @80% load: X8 reduction Hot-Modules in Wormhole NoCs 23 The HMs are better utilized Significant differences in BW! No allocation control With allocation control Flows destined at HM1 1HM1 2HM1 3HM1 4HM1 9HM1 Flows destined at HM2 10HM1 11HM1 8HM2 10HM2 11HM2 12HM2 Total Without regulation, the hot-modules are only 60% utilized - Traffic to one HM blocks the traffic to the other! May 2007 Hot-Modules in Wormhole NoCs 24 Hot-Module Placement May 2007 Hot-Modules in Wormhole NoCs 25 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 2007 Hot-Modules in Wormhole NoCs 26 Hot-Modules, Cool NoCs! Thank you! Questions? [email protected] QNoC Research Group May 2007 Hot-Modules in Wormhole NoCs Module Module Module Module Module Module Module Module Module Module Module Module QNoC Research Group 27
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