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NEMU(NJU Emulator) is a simple but complete full-system emulator designed for teaching purpose. Originally it supports x86, mips32, riscv64, and riscv32. This repo only guarantees the support for riscv64.
The main features of NEMU include
NEMU plays the following roles in XiangShan ecosystem:
NEMU can be used as a reference design to validate the correctness of XiangShan processor or XS-GEM5. Typical workflow is as follows. Concrete instructions are described in Section build-NEMU-as-ref.
The typical flow for running workloads is similar for NEMU, XS-GEM5, and XiangShan processor. All of them only support full-system simulation. To prepare workloads for full-system simulation, users need to either build a baremetal app or running user programs in an operating system.
Because most of the enterprise users and researchers are more interested in running larger workloads, like SPECCPU, on XS-GEM5 or XiangShan processor. To reduce the simulation time of detailed simulation, NEMU serves as a checkpoint producer. The flow for producing and running checkpoints is as follows. The detailed instructions for each step is described in Section Howto.
Because different distributions have different package management tools, the installation commands are different. For Ubuntu, users can install the dependencies with the following command:
apt install build-essential man gcc gdb git libreadline-dev libsdl2-dev zstd libzstd-dev
To build NEMU as reference design, run
make menuconfig # at the first time when NEMU is downloaded
make xxx-ref_defconfig
make -j
./build/riscv64-nemu-interpreter-so is the reference design.
Specifically, xxx-ref_defconfig varies for different ISA extensions.
| rv64gcb | rv64gcbh | rv64gcbv |
|---|---|---|
| riscv64-xs-ref_defconfig | riscv64-rvh-ref_defconfig | riscv64-rvv-ref_defconfig |
To test XS-GEM5 against NEMU, refer to the doc of XS-GEM5 Difftest.
To test XiangShan processor against NEMU, run
./emu \
-i test_workload.bin \
--diff $NEMU_HOME/build/riscv64-nemu-interpreter-so \
2> perf.out
Details can be found in the tutorial of XiangShan.
As described in the workflow, NEMU either takes a baremetal app or an operating system image as input.
For baremetal app, Abstract Machine is a light-weight baremetal library. Common simple apps like coremark and dhrystone can be built with Abstract Machine.
For build operating system image, Please read the doc to build Linux.
Then modify NEMU_HOME and BBL_PATH in $NEMU_HOME/scripts/checkpoint_example/checkpoint_env.sh and the workload parameter passed to the function in each example script to get started.
Please read the doc to generate checkpoint
Run a checkpoint with XiangShan processor
./build/emu -i /path/to/a/checkpoint.gz
Run checkpoints with XS-GEM5: the doc to run XS-GEM5
Read the source code of GCPT restorer
Because we restore checkpoint in M mode, and the PC of returning to user mode is stored in EPC register. This recovery method will break the architecture state (EPC) if the checkpoint is produced in M mode. In contrast, if the checkpoint is produced in S mode or U mode, the return process is just like a normal trap return, which will not break the architecture state.
Please use master branch. The checkpoint related code is not merged from tracing branch into master
First, make sure you have obtained a checkpoint.gz, not a bbv.gz. Then, see the doc to run checkpoints.
First, make sure interval size is smaller than total instruction counter of the application. Second, it is not necessary to produce checkpoints for small applications with few intervals.
Typical sampling interval size used in architecture research is 10M-200M, while typical warmup interval size is 20M-100M. It depends on your cache size and use case. For example, when studying cache's temporal locality, it is better to use a larger interval size (>=50M).
The simulation time depends on IPC of the application and the complexity of the CPU model. For Verilator simulation of XiangShan processor, the simulation time varies from hours to days. For XS-GEM5, the simulation time varies typically ranges from 6 minutes to 1 hour.
First, check FAQs of building Linux kernel for XiangShan
Then, try to search solution in issue list of NEMU and issue list of XiangShan doc.
Finally, if you cannot find a solution, please make a new issue in XiangShan doc.
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