Leandro Soares Indrusiak http://www-users.cs.york.ac.uk/lsi Dagstuhl - PowerPoint PPT Presentation

Department of Computer Science Mixed Criticality Support on Networks-on-Chip Leandro Soares Indrusiak http://www-users.cs.york.ac.uk/lsi Dagstuhl Seminar 15121 – March 2015

Mixed Criticality Support on NoCs | L. S. Indrusiak Many-Core Systems  Many-core systems present a shift towards communication-centric design  abundant computation resources  shared communication media  Inter-core communication architectures  point-to-point  on-chip bus  network-on-chip 2

Mixed Criticality Support on NoCs | L. S. Indrusiak Networks-on-Chip  Communication infrastructure based on links and routers that interconnect cores providing packet-based data transfer R R R  Low capacitive load and short wires  Scalable throughput C C C  Point to point connectivity R R R  Communication parallelism Link C C C  Shared media R R R • Reusability Router C C C Core 3

Mixed Criticality Support on NoCs | L. S. Indrusiak NoC parallelism and scalability CPU I/O CPU CPU Multiple connections simultaneously RAM CPU CPU CPU 4

Mixed Criticality Support on NoCs | L. S. Indrusiak NoC communication interference CPU I/O CPU CPU link contention leads to latency variability RAM CPU CPU CPU 5

Mixed Criticality Support on NoCs | L. S. Indrusiak Time predictability and isolation  Full traffic separation (i.e. no packet blocking)  deterministic routing, fully disjoint routes (e.g. Hermes)  multiple overlay networks (e.g. Tilera), contention over NIs and memory still possible  circuit switching (e.g. PNoC), unpredictable circuit setup time  Virtual traffic separation  fixed TDM traffic slotting (e.g. Aethereal, AElite)  rate controlling (e.g. Nostrum, IDAMC)  priority-arbitrated virtual channels (e.g. QNoC) 6

Mixed Criticality Support on NoCs | L. S. Indrusiak Priority preemptive virtual channels highest priority highest priority priority ID with remaining credit with remaining credit R R R data_out data_in C C C … … routing routing credit_out credit_in R & & R R transmission transmission control control C C C R R R … … C C C 7

Mixed Criticality Support on NoCs | L. S. Indrusiak Packet latency  Packet flows suffer interference from other flows that have higher priority and share at least one link  indirect interference also plays a role  Worst case latency can be found by an application of Response Time Analysis Z. Shi, A. Burns: Real-Time Communication Analysis for On-Chip Networks with Wormhole Switching. NOCS 2008: 161-170 8

Mixed Criticality Support on NoCs | L. S. Indrusiak Mixed criticality packet flows  Possible sources of uncertainty R R R  packet length  packet flow period C C C  jitter R R R C C C  All packet flows must be R R R schedulable under normal mode C C C  Runtime monitoring detects when packets go “beyond network interface normal” 9

Mixed Criticality Support on NoCs | L. S. Indrusiak Mixed criticality packet flows  Runtime monitoring detects when packets go “beyond R R R normal” C C C R R R  if it is a LO-CRIT packet exceeding its C C C normal budget, reject it R R R  if it is a HI-CRIT packet exceeding its normal budget, signalise a mode C C C change to the NoC, aiming to notify that a service degradation to LO-CRIT mode change notification packets is needed so that HI-CRIT packets can still be scheduled despite of potential increase of interference due to overbudget packets 10

Mixed Criticality Support on NoCs | L. S. Indrusiak Mixed criticality packet flows  Two mode change R R R propagation protocols C C C  WPMC: mode change flag R R R “piggybacked” on packets that pass through a router that has C C C changed mode R R R C C C  WPMC-FLOOD: mode change is flooded to the entire NoC A. Burns, J. Harbin, L. S. Indrusiak: A Wormhole NoC Protocol for Mixed Criticality Systems. RTSS 2014: 184-195 11

Mixed Criticality Support on NoCs | L. S. Indrusiak Mixed criticality packet flows  Two mode change R R R propagation protocols C C C  WPMC: mode change flag R R R “piggybacked” on packets that pass through a router that has changed C C C mode R R R C C C  WPMC-FLOOD: mode change is flooded to the entire NoC L. S. Indrusiak , J. Harbin, A. Burns: Average and Worst-Case Latency Improvements in Mixed-Criticality Wormhole Networks-on-Chip. ECRTS 2015 (submitted). 12

Mixed Criticality Support on NoCs | L. S. Indrusiak Mixed criticality packet flows  Two HI-CRIT mode arbitration R R R schemes C C C  routers that change mode ignore R R R arbitration requests of LO-CRIT packets C C C R R R  routers that change mode arbitrate C C C links in criticality order (HI-CRIT then LO-CRIT), and in priority order within the same criticality A. Burns, J. Harbin, L. S. Indrusiak: A Wormhole NoC Protocol for Mixed Criticality Systems. RTSS 2014: 184-195 13

Mixed Criticality Support on NoCs | L. S. Indrusiak Mixed criticality packet flows  Two HI-CRIT mode arbitration R R R schemes C C C  routers that change mode ignore R R R arbitration requests of LO-CRIT packets C C C R R R  routers that change mode arbitrate C C C links in criticality order (HI-CRIT then LO-CRIT), and in priority order within the same criticality L. S. Indrusiak , J. Harbin, A. Burns: Average and Worst-Case Latency Improvements in Mixed-Criticality Wormhole Networks-on-Chip. ECRTS 2015 (submitted). 14

Mixed Criticality Support on NoCs | L. S. Indrusiak Mixed criticality packet flows  Response Time Analysis formulations for each of the protocols were developed  Evaluation with synthetic flowsets (against no criticality awareness and criticality-monotonic arbitration) and cycle-accurate NoC simulation  WPMC-FLOOD slightly better in general, significantly better in stress scenarios  Less restrictive arbitration allows LO-CRIT packets to flow when there are no HI-CRIT packets or when they are blocked due to interferences 15

Mixed Criticality Support on NoCs | L. S. Indrusiak Mixed criticality packet flows 16

Mixed Criticality Support on NoCs | L. S. Indrusiak Mixed criticality packet flows 17

Mixed Criticality Support on NoCs | L. S. Indrusiak Open issues  Handle recovery  how to detect that there are no further overbudget packets in the network?  how to make sure their impact on the network (i.e. additional interference) is no longer there?  how to notify all routers to return to normal mode?  Explore optimisations on task allocation and packet routing  Improved experimental work  how many packet flows are HI-CRIT and how many are LO-CRIT?  how much overbudget can HI-CRIT reasonably be? 18

Department of Computer Science Mixed Criticality Support on Networks-on-Chip Leandro Soares Indrusiak Alan Burns James Harbin Dagstuhl Seminar 15121 – March 2015