README for Garnet3.0
Written By: Tushar Krishna (tushar@ece.gatech.edu)
Last Updated: Sep 9, 2020
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Garnet Network Parameters and Setup:
- GarnetNetwork.py
* defaults can be overwritten from command line (see configs/network/Network.py)
- GarnetNetwork.hh/cc
* sets up the routers and links
* collects stats
CODE FLOW
- NetworkInterface.cc::wakeup()
* Every NI connected to one coherence protocol controller on one end, and one router on the other.
* receives messages from coherence protocol buffer in appropriate vnet and converts them into network packets and sends them into the network.
* garnet adds the ability to capture a network trace at this point.
* receives flits from the network, extracts the protocol message and sends it to the coherence protocol buffer in appropriate vnet.
* manages flow-control (i.e., credits) with its attached router.
* The consuming flit/credit output link of the NI is put in the global event queue with a timestamp set to next cycle.
The eventqueue calls the wakeup function in the consumer.
- NetworkLink.cc::wakeup()
* receives flits from NI/router and sends it to NI/router after m_latency cycles delay
* Default latency value for every link can be set from command line (see configs/network/Network.py)
* Per link latency can be overwritten in the topology file
* The consumer of the link (NI/router) is put in the global event queue with a timestamp set after m_latency cycles.
The eventqueue calls the wakeup function in the consumer.
- Router.cc::wakeup()
* Loop through all InputUnits and call their wakeup()
* Loop through all OutputUnits and call their wakeup()
* Call SwitchAllocator's wakeup()
* Call CrossbarSwitch's wakeup()
* The router's wakeup function is called whenever any of its modules (InputUnit, OutputUnit, SwitchAllocator, CrossbarSwitch) have
a ready flit/credit to act upon this cycle.
- InputUnit.cc::wakeup()
* Read input flit from upstream router if it is ready for this cycle
* For HEAD/HEAD_TAIL flits, perform route computation, and update route in the VC.
* Buffer the flit for (m_latency - 1) cycles and mark it valid for SwitchAllocation starting that cycle.
* Default latency for every router can be set from command line (see configs/network/Network.py)
* Per router latency (i.e., num pipeline stages) can be set in the topology file
- OutputUnit.cc::wakeup()
* Read input credit from downstream router if it is ready for this cycle
* Increment the credit in the appropriate output VC state.
* Mark output VC as free if the credit carries is_free_signal as true
- SwitchAllocator.cc::wakeup()
* Note: SwitchAllocator performs VC arbitration and selection within it.
* SA-I (or SA-i): Loop through all input VCs at every input port, and select one in a round robin manner.
* For HEAD/HEAD_TAIL flits only select an input VC whose output port has at least one free output VC.
* For BODY/TAIL flits, only select an input VC that has credits in its output VC.
* Place a request for the output port from this VC.
* SA-II (or SA-o): Loop through all output ports, and select one input VC (that placed a request during SA-I) as the winner for this output port in a round robin manner.
* For HEAD/HEAD_TAIL flits, perform outvc allocation (i.e., select a free VC from the output port).
* For BODY/TAIL flits, decrement a credit in the output vc.
* Read the flit out from the input VC, and send it to the CrossbarSwitch
* Send a increment_credit signal to the upstream router for this input VC.
* for HEAD_TAIL/TAIL flits, mark is_free_signal as true in the credit.
* The input unit sends the credit out on the credit link to the upstream router.
* Reschedule the Router to wakeup next cycle for any flits ready for SA next cycle.
- CrossbarSwitch.cc::wakeup()
* Loop through all input ports, and send the winning flit out of its output port onto the output link.
* The consuming flit output link of the router is put in the global event queue with a timestamp set to next cycle.
The eventqueue calls the wakeup function in the consumer.
If a clock domain crossing(CDC) or Serializer-Deserializer unit is
instantiated, then the Network Brisge takes over the flit in HeteroGarnet.
- NetworkBridge::wakeup()
* Check if SerDes is enabled and do appropriate calculations for
serializing or deserializing the flits
* Check if CDC is enabled and schedule all the flits according
to the consumers clock domain.
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