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gem5-stable
README.md
README.md

Pendulum: Predictable Time-based Cache Coherence Protocol for Mixed-Time Critical Multi-Cores

  • This is the repository for the source code of Pendulum in gem5.

Pendulum specific files:

  • Gem5 is modified to support snooping bus architecture with a criticality-aware arbitration scheme.
  • File build_opts/X86_MSI_Snooping_Time_based provides the build configuration settings (architecure and the protocol to be used).
  • The configuration file for Pendulum in configs/ruby/X86_MSI_Snooping_Time_based.py provides settings for the memory hierarchy and network.
  • The Pendulum protocol states and transitions are included in src/mem/protocol/X86_MSI_Snooping_Time_based* files. They are written in [SLICC] (http://gem5.org/SLICC).
  • The bus arbitration details are included in src/mem/ruby/network/simple/Throttle.cc
  • Gem5 is also extended to support trace-based simulations by modifying the Ruby Random Tester to read traces from a trace.trc file.
    • Trace.trc file contains all requests in the form - Addr Read/Write ArrivalTimeOfRequest.
    • The requests in the trace.trc file are replicated on all cores with same time-stamp. This gives maximum sharing of data across the cores.

Pendulum initial configurations:

  • The configuration details for the system are provided in src/cpu/testers/rubytest/Trace.hh
    • NPROC_C - number of HRT cores.
    • NPROC_NC - number of SRT cores.
    • NPROC - total number of cores - NPROC_C+NPROC_NC.
    • SLOT_WIDTH - TDM slot width set in terms of cycles.
    • ALL_CRITICAL - This is set to 1 when we want to disable mixed criticality and use all the cores with same level of criticality.
      • While using ALL_CRITICAL mode, NPROC_C should be set equal to NPROC.
    • TRACE - This is set to 1 to run trace-based simulations.
    • SYNTH - this is set to 1 to run different sequence of memory instructions for different cores using Ruby Random Tester.
  • The initial values for timers v(cr,cr), v(cr,ncr), v(ncr,cr) and v(ncr,ncr) can be set at run-time with the options timeout_cc, timeout_cn, timeout_nc and timeout_nn in terms of cycles.

Building gem5 with Pendulum protocol:

  • scons ./build/X86_MSI_Snooping_Time_based/gem5.opt -j8

Running gem5:

  • To run Pendulum, gem5 should be run with the options --ruby, --cpu-type=timing and --mem-type=SimpleMemory (in-order cores).

  • This version of gem5 accepts only static executables.

  • Multi-threaded workloads should be compiled with static flag and include [m5threads] (http://repo.gem5.org/m5threads), pthread library for gem5, instead of the standard pthread library.

  • Running multithreaded application, say FFT of SPLASH-2, on gem5:

    • ./build/X86_MSI_Snooping_Time_based/gem5.opt ./configs/example/se.py --ruby -n4 --cpu-type=timing --l1d_size=16kB --l1i_size=16kB --l1d_assoc=1 --l1i_assoc=1 --mem-size=4194304kB --topology=Crossbar --cpu-clock=2GHz --ruby-clock=2GHz --mem-type=SimpleMemory --timeout_cc=200 --timeout_cn=400 --timeout_nc=100 --timeout_nn=200 -c /PATH_TO_SPLASH2/codes/kernels/fft/fft -o '-m 10 -p 4 -t'

  • Running trace-based simulation:

    • ./build/X86_MSI_Snooping_Time_based/gem5.opt ./configs/example/ruby_random_test.py --ruby -n4 --mem-size=4194304kB --topology=Crossbar --cpu-clock=2GHz --ruby-clock=2GHz --mem-type=SimpleMemory --maxloads=1000000 --timeout_cc=200 --timeout_cn=400 --timeout_nc=100 --timeout_nn=200 --wakeup_freq=1
    • The latency in src/mem/SimpleMemory.py needs to be set to 22ns to trace-based simulation.

  • --debug-flags can be enabled to understand the network and protocol details.

  • Sample trace files are included in gem5-stable/.

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