I'm writing because I am currently working on a project using the gem5 simulator to simulate an ARM bigLITTLE configuration where the big CPU cluster has an L2 but the little CPU cluster does not. That is, I would like to simulate a system in which the little cores are even simpler than their default configuration. I am running the project using the full system bigLITTLE file (i.e., gem5/configs/example/fs_bigLITTLE.py). Is it possible to configure the system in this way?
My initial thought was to modify the python file so that the little cluster configuration is composed of the following:
class LittleCluster(devices.CpuCluster):
def __init__(self, system num_cpus, cpu_clock, cpu_voltage="1.0V"):
cpu_config = [ ObjectList.cpu_list.get("MinorCPU"), devices.L1I, devices.L1D, devices.WalkCache, None]
super(LittleCluster, self).__init__(system, num_cpus, cpu_clock, cpu_voltage, *cpu_config)
or, in layman's terms, provide None as the SimObject class name for the L2. Unfortunately, as one might expect, this causes the system to crash as the ...
My next idea was to write a new SimObject called EmptyCache that inherits the Cache class from gem5, but does nothing. That is, on every call access to the cache this object would return false, and it would be configured to have no tag, data, or response latency. However, this causes coherence issues with the L1 caches in the little cluster, so I then changed it so that it evicts any cache block that it "hits" before returning false (the following is based on a prior post to the gem5-users mailing list: https://www.mail-archive.com/[email protected]/msg16882.html)
EmptyCache::access(PacketPtr pkt, CacheBlk *&blk, Cycles &lat, PacketList &writebacks)
{
if (Cache::access(pkt, blk, lat, writebacks) {
Cache::evictBlock(blk);
}
return false;
}
This seems to solve the coherence issues above with the L1 caches, but this seemed to cause coherence issues in the memory bus (which implements the SystemXBar class (which implements the CoherentXBar class)).
At this point, I feel pretty much stuck and would appreciate any advice that you could provide! Thank you!
