How is the CPU speed implemented in GEM5? I'm browsing the source code, but can't seem to find the portion that actually establishes how many simulation ticks actually constitute a CPU cycle.
I'm trying to find this out for the following reason: - I generated memory access traces with GEM5. Each access in the trace has a timestamp (which is measured in 1 ps ticks). - However, when I divide the alleged processor cycle time by the timestamps in the trace, i'm getting a fraction (instead of an integer). I'll elaborate. I use the following command to invoke gem5: ./gem5.opt --trace-file=output.txt configs/example/se.py --cpu-type=detailed --sys-clock=1.1GHz --cpu-clock=1.1GHz --caches -c a2time01 This combined to a small modification in the SimpleDRAM code yielded the trace below (only showing a couple of lines...): 1818: system.physmem: Memory request of 64 bytes for address: READ b80 39087: system.physmem: Memory request of 64 bytes for address: READ bc0 78174: system.physmem: Memory request of 64 bytes for address: READ c00 82846: system.physmem: Memory request of 64 bytes for address: READ 5e40 87518: system.physmem: Memory request of 64 bytes for address: READ 87f00 92190: system.physmem: Memory request of 64 bytes for address: READ bc0 122715: system.physmem: Memory request of 64 bytes for address: READ 5e80 128169: system.physmem: Memory request of 64 bytes for address: READ 60c0 162711: system.physmem: Memory request of 64 bytes for address: READ 5ec0 170892: system.physmem: Memory request of 64 bytes for address: READ 87dc0 (the number on the left represents the simulation tick). My point is: a 1.1GHz frequency means a cycle time of approx. 909.09ps. Given the 1ps simulation tick from GEM5, I was expecting each processor cycle to contain 909 simulation ticks. Although most of the trace timestamps are divisible by 909, there are counter examples: 92190/909=101.4191419141914191419141914191419141914191419141914191419141914191\ 419141914191419141914191419141914191 This makes no sense, given that the processor and the system clock are the same. Although this is not exactly important for my experiments, it is really bothering me. I need to know this so I can have some peace of mind :) Thanks in advance, Leonardo Ecco. _______________________________________________ gem5-users mailing list [email protected] http://m5sim.org/cgi-bin/mailman/listinfo/gem5-users
