Running gem5
Contents
Usage
The gem5 command line has four parts, the gem5 binary, options for the binary, a simulation script, and options for the script. The options that are passed to the gem5 binary and those passed to the script are handled separately, so be sure any options you use are being passed to the right component.
% <gem5 binary> [gem5 options] <simulation script> [script options]
gem5 Options
Running gem5 with the "-h" flag prints a help message that includes all of the supported simulator options. Here's a snippet:
% build/ALPHA/gem5.debug -h
Usage
=====
gem5.debug [gem5 options] script.py [script options]
Copyright (c) 2001-2008 The Regents of The University of Michigan All Rights
Reserved
gem5 is copyrighted software; use the --copyright option for details.
Options
=======
--version show program's version number and exit
--help, -h show this help message and exit
--build-info, -B Show build information
--copyright, -C Show full copyright information
--readme, -R Show the readme
--outdir=DIR, -d DIR Set the output directory to DIR [Default: m5out]
--redirect-stdout, -r Redirect stdout (& stderr, without -e) to file
--redirect-stderr, -e Redirect stderr to file
--stdout-file=FILE Filename for -r redirection [Default: simout]
--stderr-file=FILE Filename for -e redirection [Default: simerr]
--interactive, -i Invoke the interactive interpreter after running the
script
--pdb Invoke the python debugger before running the script
--path=PATH[:PATH], -p PATH[:PATH]
Prepend PATH to the system path when invoking the
script
--quiet, -q Reduce verbosity
...
The default options that gem5 uses to run can be set by creating an ~/.m5/options.py file and placing options that you are interested in there. For example, if you would like to always redirect standard error and out to a file you could add: options.stdout_file=simout to options.py.
Script Options
The script section of the command line begins with a path to your script file and includes any options that you'd like to pass to that script. Most Example scripts allow you to pass a '-h' or '--help' flag to the script to see script specific options. An example is as follows:
gem5 compiled Apr 2 2011 00:57:11
gem5 started Apr 3 2011 21:16:02
gem5 executing on zooks
command line: build/ALPHA/gem5.opt configs/example/se.py -h
Usage: se.py [options]
Options:
-h, --help show this help message and exit
-c CMD, --cmd=CMD The binary to run in syscall emulation mode.
-o OPTIONS, --options=OPTIONS
The options to pass to the binary, use " " around the
entire string
-i INPUT, --input=INPUT
Read stdin from a file.
--output=OUTPUT Redirect stdout to a file.
--errout=ERROUT Redirect stderr to a file.
--ruby
-d, --detailed
-t, --timing
--inorder
-n NUM_CPUS, --num-cpus=NUM_CPUS
--caches
--l2cache
--fastmem
--clock=CLOCK
--num-dirs=NUM_DIRS
--num-l2caches=NUM_L2CACHES
--l1d_size=L1D_SIZE
--l1i_size=L1I_SIZE
--l2_size=L2_SIZE
--l1d_assoc=L1D_ASSOC
--l1i_assoc=L1I_ASSOC
--l2_assoc=L2_ASSOC
...
The script file documentation page (Configuration / Simulation Scripts) describes how to write your own simulation scripts, and the Options section explains how to add your own command line options. The simulation scripts that are most commonly used are se.py and fs.py. These scripts are present in configs/examples directory. se.py is meant for simulation using the system call emulation mode, while fs.py is for full-system simulations. In most cases, it should be possible to use either of these two scripts without any modifications. Understanding how these two scripts work can help you decide on what modifications are required for your particular case.
System Call Emulation (SE) Mode
In this mode, one only needs to specify the binary file to be simulated. This binary file can be statically/dynamically linked. configs/examples/se.py is used for configuring and running simulations in this mode. What follows is probably the simplest example of how to use se.py. The binary file to simulated is specified with option -c.
$ ./build/ALPHA/gem5.opt ./configs/example/se.py -c ./tests/test-progs/hello/bin/alpha/linux/hello gem5 Simulator System. http://gem5.org gem5 is copyrighted software; use the --copyright option for details. gem5 compiled Mar 2 2014 00:06:39 gem5 started Mar 4 2014 10:52:10 gem5 executing on $ command line: ./build/ALPHA/gem5.opt ./configs/example/se.py -c ./tests/test-progs/hello/bin/alpha/linux/hello Global frequency set at 1000000000000 ticks per second 0: system.remote_gdb.listener: listening for remote gdb #0 on port 7000 **** REAL SIMULATION **** info: Entering event queue @ 0. Starting simulation... info: Increasing stack size by one page. Hello world! Exiting @ tick 3233000 because target called exit()
Specifying Command-Line Arguments
In order to pass command line arguments to a binary you can use --options="arg1 arg2 ..." to specify them as a script option in your simulation command.
Full System (FS) Mode
This mode simulates a complete system which provides an operating system based simulation environment. For full system mode, you can use the file configs/example/fs.py for configuration and simulation. Sensible default values have been set for the options that this script uses. We provide examples for ALPHA and ARM based full system simulations.
Booting Linux
We'll assume that you've already built an ALPHA version of the gem5 simulator, and downloaded and installed the full-system binary and disk image files. Then you can run the fs.py configuration file in the gem5/configs/examples directory. For example:
% build/ALPHA/gem5.debug -d /tmp/output configs/example/fs.py
gem5 Simulator System
Copyright (c) 2001-2006
The Regents of The University of Michigan
All Rights Reserved
gem5 compiled Aug 16 2006 18:51:57
gem5 started Wed Aug 16 21:53:38 2006
gem5 executing on zeep
command line: ./build/ALPHA/gem5.debug configs/example/fs.py
0: system.tsunami.io.rtc: Real-time clock set to Sun Jan 1 00:00:00 2006
Listening for console connection on port 3456
0: system.remote_gdb.listener: listening for remote gdb #0 on port 7000
warn: Entering event queue @ 0. Starting simulation...
<...simulation continues...>
Basic Operation
By default, the fs.py script boots Linux and starts a shell on the system console. To keep console traffic separate from simulator input and output, this simulated console is associated with a TCP port. To interact with the console, you must connect to the port using a program such as telnet, for example:
% telnet localhost 3456
Telnet's echo behavior doesn't work well with gem5, so if you are using the console regularly, you probably want to use M5term instead of telnet. By default gem5 will try to use port 3456, as in the example above. However, if that port is already in use, it will increment the port number until it finds a free one. The actual port number used is printed in the gem5 output.
In addition to loading a Linux kernel, gem5 mounts one or more disk images for its filesystems. At least one disk image must be mounted as the root filesystem. Any application binaries that you want to run must be present on these disk images. To begin running benchmarks without requiring an interactive shell session, gem5 can load .rcS files that replace the normal Linux boot scripts to directly execute from after booting the OS. These .rcS files can be used to configure ethernet interfaces, execute special gem5 instructions, or begin executing a binary on the disk image. The pointers for the linux binary, disk images, and .rcS files are all set in the simulation script. (To see how these files work, see Configuration / Simulation Scripts.) Examples: Going into / of root filesystem and typing ls will show:
benchmarks etc lib mnt sbin usr bin floppy lost+found modules sys var dev home man proc tmp z
Snippet of an .rcS file:
echo -n "setting up network..." /sbin/ifconfig eth0 192.168.0.10 txqueuelen 1000 /sbin/ifconfig lo 127.0.0.1 echo -n "running surge client..." /bin/bash -c "cd /benchmarks/surge && ./Surge 2 100 1 192.168.0.1 5. echo -n "halting machine" m5 exit
m5term
The m5term program allows the user to connect to the simulated console interface that full-system gem5 provides. Simply change into the util/term directory and build m5term:
% cd gem5/util/term % make gcc -o m5term term.c % make install sudo install -o root -m 555 m5term /usr/local/bin
The usage of m5term is:
./m5term <host> <port> <host> is the host that is running gem5 <port> is the console port to connect to. gem5 defaults to using port 3456, but if the port is used, it will try the next higher port until it finds one available. If there are multiple systems running within one simulation, there will be a console for each one. (The first system's console will be on 3456 and the second on 3457 for example) m5term uses '~' as an escape character. If you enter the escape character followed by a '.', the m5term program will exit.
m5term can be used to interactively work with the simulator, though users must often set various terminal settings to get things to work
A slightly shortened example of m5term in action:
% m5term localhost 3456 ==== m5 slave console: Console 0 ==== M5 console Got Configuration 127 memsize 8000000 pages 4000 First free page after ROM 0xFFFFFC0000018000 HWRPB 0xFFFFFC0000018000 l1pt 0xFFFFFC0000040000 l2pt 0xFFFFFC0000042000 l3pt_rpb 0xFFFFFC0000044000 l3pt_kernel 0xFFFFFC0000048000 l2reserv 0xFFFFFC0000046000 CPU Clock at 2000 MHz IntrClockFrequency=1024 Booting with 1 processor(s) ... ... VFS: Mounted root (ext2 filesystem) readonly. Freeing unused kernel memory: 480k freed init started: BusyBox v1.00-rc2 (2004.11.18-16:22+0000) multi-call binary PTXdist-0.7.0 (2004-11-18T11:23:40-0500) mounting filesystems... EXT2-fs warning: checktime reached, running e2fsck is recommended loading script... Script from M5 readfile is empty, starting bash shell... # ls benchmarks etc lib mnt sbin usr bin floppy lost+found modules sys var dev home man proc tmp z #
Full System Benchmarks
We have several full-system benchmarks already up and running. The binaries are available in the disk images you can obtain/download from us, and the .rcS files are in the gem5/configs/boot/ directory. To run any of them, you merely need to set the benchmark option to the name of the test you want to run. For example:
%./build/ALPHA/gem5.opt configs/example/fs.py -b NetperfMaerts
To see a comprehensive list of all benchmarks available:
%./build/ALPHA/gem5.opt configs/examples/fs.py -h
Experimenting with DVFS
This is a quick hands-on tutorial to start a DVFS-enabled system where the Linux DVFS governors can change voltage and frequencies of the ongoing simulation. Right now, the driver and interface components live in ARM-specific parts of the Linux kernel / gem5, but there is no fundamental reason why this could not be ported to work on other architectures, too.
Quick Instructions
These instructions apply for a Ubuntu-based machine, but can be easily adapted / extended etc. for other use cases and systems.
- Get gem5 with the proper changesets added
- Anything after [1]
hg clone http://repo.gem5.org/gem5
scons build/ARM/gem5.opt -j 8
git clone --depth 10 https://gem5.googlesource.com/arm/linux-arm-legacy
sudo apt-get install gcc-arm-linux-gnueabihf
- See also Linux_kernel
make ARCH=arm vexpress_gem5_dvfs_defconfig make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- -j8
ls arch/arm/boot/dts/vexpress-v2*dvfs*
wget http://www.gem5.org/dist/current/arm/arm-system-2013-07.tar.bz2 tar xvjf arm-system-2013-07.tar.bz2
- Enable and link the energy controller / DVFS handler
patch -p1 << EOF diff --git a/configs/example/fs.py b/configs/example/fs.py --- a/configs/example/fs.py +++ b/configs/example/fs.py @@ -106,7 +106,11 @@ # Create a source clock for the CPUs and set the clock period test_sys.cpu_clk_domain = SrcClockDomain(clock = options.cpu_clock, voltage_domain = - test_sys.cpu_voltage_domain) + test_sys.cpu_voltage_domain, + domain_id = 0) + + test_sys.dvfs_handler.domains = test_sys.cpu_clk_domain + test_sys.dvfs_handler.enable = 1 if options.kernel is not None: test_sys.kernel = binary(options.kernel) EOF
- Can also change the clock frequencies here, or from command line
M5_PATH=$(pwd)/.. ./build/ARM/gem5.opt --debug-flags=DVFS,EnergyCtrl \ --debug-file=dfvs_debug.log configs/example/fs.py --cpu-type=AtomicSimpleCPU \ -n 2 --machine-type=VExpress_EMM --kernel=../linux-linaro-tracking-gem5/vmlinux \ --dtb-filename=../linux-linaro-tracking-gem5/arch/arm/boot/dts/\ vexpress-v2p-ca15-tc1-gem5_dvfs_2cpus.dtb \ --disk-image=../disks/arm-ubuntu-natty-headless.img \ --cpu-clock=\['1 GHz','750 MHz','500 MHz'\]
util/term/m5term 3456 <login> cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies echo 750187 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
Futher Experiments
- Set up different voltages for the operating points
patch -p1 < EOF diff --git a/configs/example/fs.py b/configs/example/fs.py --- a/configs/example/fs.py +++ b/configs/example/fs.py @@ -101,12 +101,16 @@ voltage_domain = test_sys.voltage_domain) # Create a CPU voltage domain - test_sys.cpu_voltage_domain = VoltageDomain() + test_sys.cpu_voltage_domain = VoltageDomain(voltage = ['1V','0.9V','0.8V']) # Create a source clock for the CPUs and set the clock period test_sys.cpu_clk_domain = SrcClockDomain(clock = options.cpu_clock, voltage_domain = - test_sys.cpu_voltage_domain) + test_sys.cpu_voltage_domain, + domain_id = 0) + + test_sys.dvfs_handler.domains = test_sys.cpu_clk_domain + test_sys.dvfs_handler.enable = 1 if options.kernel is not None: test_sys.kernel = binary(options.kernel) EOF - Per-core DVFS
- Set up separate clock (and voltage) domains per core
- Separate clock domains need separate clusters in the device tree
diff -u linux-linaro-tracking-gem5/arch/arm/boot/dts/\ vexpress-v2p-ca15-tc1-gem5_dvfs_{,per_core_}4cpus.dts</code> - Change the socket_id to have a separate socket per CPU core
