The lectures on NoC deadlocks on my website might help understand the problem: http://tusharkrishna.ece.gatech.edu/wp-content/uploads/sites/175/2016/10/L05-Deadlocks-I.pdf http://tusharkrishna.ece.gatech.edu/wp-content/uploads/sites/175/2016/10/L06-Deadlocks-II.pdf http://tusharkrishna.ece.gatech.edu/teaching/icn_s17/
By default any VC can be selected as you rightly pointed out. This means a cyclic dependence can form leading to a deadlock. To avoid it, one technique is to partition the VCs into 2 halves, and require all flits crossing a specific link to switch from the first half to the second half. Flits can cross from VC 0 to VC 1, but not from VC 1 to VC 0, thereby ensuring no cyclic dependence. To implement this, you need to hack into the VC select code. [The same holds true in Garnet1.0 as well - it will also deadlock with a Torus]. If you want to use a Torus topology, this is something that needs to be implemented and not supported out of the box in garnet (yet). Cheers, Tushar On Jul 24, 2017, at 10:36 AM, F. A. Faisal <dipu.7...@gmail.com<mailto:dipu.7...@gmail.com>> wrote: Plus... The default weight based routing selects the free VC. If so, then why I need to do the VC partitioning as you mentioned in the Torus network. VC Selection (VS): The winner of SA selects a free VC (if HEAD/HEAD_TAIL flit) from its output port. I think this is a very important issue for all the users of garnet 2,0. I would like to solve this. Thanks again. Faisal On Mon, Jul 24, 2017 at 11:21 PM, F. A. Faisal <dipu.7...@gmail.com<mailto:dipu.7...@gmail.com>> wrote: Thanks a lot for reply. This is little bit terrible news for me. However, as far I know garnet1.0 don't have the deadlock issue with Torus. Please let me know how can I implement a VC partitioning scheme. Is it possible? I can configure the routing algorithm with particular channel selection, but I have no idea of VC partitioning in gem5. Please help me. Thanks again. Faisal On Mon, Jul 24, 2017 at 10:33 PM, Krishna, Tushar <tus...@ece.gatech.edu<mailto:tus...@ece.gatech.edu>> wrote: Hi Faisal, The Torus topology deadlocks as it has rings in each dimension unless one implements a VC partitioning scheme or bubble flow control. That's why I removed torus from the default topologies provided by garnet2.0. If you implement torus, you will have to implement deadlock freedom. Cheers, Tushar On Jul , 2017, at 5:56 PM, F. A. Faisal <dipu.7...@gmail.com<mailto:dipu.7...@gmail.com>> wrote: Dear All, I like to simulate the synthetic traffic analysis for Torus for 256 nodes with uniform traffic. However, the network is showing latency degradation after 0.14 injection rate (flit latency = 33.044985 for 0.14 and flit latency = 38.244770 for 0.13 ), which could be the possible case of network deadlocked. I configured the garnet 2.0 with all the default settings (4 vc + 16 bandwith factor) and Mesh network is also performing properly. As the number of VC is 4, Torus should not be in a deadlock. I also like to share the network file as attachment. And please consider the simulation condition as below- ./build/Garnet_standalone/gem5.debug configs.py/example/garnet_synth_traffic --num-cpus=256 --num-dirs=256 --network=garnet2.0 --topology=Torus_XY --mesh-rows=16 --sim-cycles=20000 --synthetic=uniform_random --injectionrate=0.14 --routing-algorithm=0 --vcs-per-vnet=4 Please let me know how to resolve this issue for Garnet 2.0. Thanks and best regards, F.A. Faisal <Torus_XY.py> _______________________________________________ gem5-users mailing list gem5-users@gem5.org<mailto:gem5-users@gem5.org> http://m5sim.org/cgi-bin/mailman/listinfo/gem5-users _______________________________________________ gem5-users mailing list gem5-users@gem5.org<mailto:gem5-users@gem5.org> http://m5sim.org/cgi-bin/mailman/listinfo/gem5-users _______________________________________________ gem5-users mailing list gem5-users@gem5.org<mailto:gem5-users@gem5.org> http://m5sim.org/cgi-bin/mailman/listinfo/gem5-users
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