24.10.3.3. Meaning of each gem5 stat
Well, run minimal examples, and reverse engineer them up!
We can start with userland/arch/x86_64/freestanding/linux/hello.S on atomic with gem5 ExecAll trace format.
./run \ --arch aarch64 \ --emulator gem5 \ --userland userland/arch/aarch64/freestanding/linux/hello.S \ --trace ExecAll \ --trace-stdout \ ;
which gives:
0: system.cpu: A0 T0 : @_start : movz x0, #1, #0 : IntAlu : D=0x0000000000000001 flags=(IsInteger)
500: system.cpu: A0 T0 : @_start+4 : adr x1, #28 : IntAlu : D=0x0000000000400098 flags=(IsInteger)
1000: system.cpu: A0 T0 : @_start+8 : ldr w2, #4194464 : MemRead : D=0x0000000000000006 A=0x4000a0 flags=(IsInteger|IsMemRef|IsLoad)
1500: system.cpu: A0 T0 : @_start+12 : movz x8, #64, #0 : IntAlu : D=0x0000000000000040 flags=(IsInteger)
2000: system.cpu: A0 T0 : @_start+16 : svc #0x0 : IntAlu : flags=(IsSerializeAfter|IsNonSpeculative|IsSyscall)
2500: system.cpu: A0 T0 : @_start+20 : movz x0, #0, #0 : IntAlu : D=0x0000000000000000 flags=(IsInteger)
3000: system.cpu: A0 T0 : @_start+24 : movz x8, #93, #0 : IntAlu : D=0x000000000000005d flags=(IsInteger)
3500: system.cpu: A0 T0 : @_start+28 : svc #0x0 : IntAlu : flags=(IsSerializeAfter|IsNonSpeculative|IsSyscall)
The most important stat of all is usually the cycle count, which is a direct measure of performance if you modelled you system well:
sim_ticks 3500 # Number of ticks simulated
Next, sim_insts and sim_ops are often critical:
sim_insts 6 # Number of instructions simulated sim_ops 6 # Number of ops (including micro ops) simulated
sim_ops is like sim_insts but it also includes gem5 microops.
In gem5 syscall emulation mode, syscall instructions are magic, and therefore appear to not be counted, that is why we get 6 instructions instead of 8.