WA-gem5

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To run workloads in gem5, we advise you to use Workload Automation (WA). This framework allows you to run workloads automatically on Android and Linux platforms. More information can be found here: https://github.com/ARM-software/workload-automation

What do I need?

To use WA together with gem5 you will need to make changes to the host system and the guest system. These changes will enable 9P over virtio, which will allow for files to be transported into the simulation.

Host system requirements

On the host system side this means that diod needs to be present. To install diod on Ubuntu you can use the following command:

sudo apt-get install diod

Guest system requirements

To enable this in the guest system we need to ensure the support is built into the kernel. To do this the following configuration options need to be set:

CONFIG_NETWORK_FILESYSTEMS=y
CONFIG_NET_9P=y
CONFIG_NET_9P_VIRTIO=y
CONFIG_9P_FS=y
CONFIG_9P_FS_POSIX_ACL=y
CONFIG_9P_FS_SECURITY=y
CONFIG_VIRTIO_BLK=y

The guest system also needs to have an m5 binary, which can be found in the gem5 repository under util/m5. The m5 binary is used for extracting files out of the simulation, checkpointing and simulation control (e.g. stats dumps, and exiting gem5). It is important that this file can be found on the path. For checkpointing to work correctly two things need to be ensured when taking the checkpoint:

  1. The virtio device is included in the system
  2. No part of the host file system is mounted by the virtio device

During boot the operating system will initialize all the drivers corresponding with which devices are present in the system. If the virtio device is not found, it cannot be used later, thus the deivce needs to be present during boot (1). Unfortunately, when checkpointing the system it is impossible (well, very hard) to give guarantees about the preservation of the state. You may add or remove files from the host system in between taking and resuming from the checkpoint. For this reason we advise to only mount the host system after restoring from the checkpoint (2).

Using gem5 with Workload Automation

WA uses agendas to specify the experiments that need to be run. An agenda is a YAML file that describes the configuration of the device, the workloads to be run, and which results to extract. It can be seen as a recipe of how to recreate an experiment. Here is an example of what an agenda looks like for gem5:

config:
    device: gem5_linux
    device_config:
        gem5_args: "configs/example/fs.py"
        gem5_vio_args: "--workload-automation-vio={}"
        username: root
        temp_dir: "/tmp"
        checkpoint: True
        run_delay: 10
    reboot_policy: never
    result_processors: [~sqlite]
    instrumentation: [~cpufreq]

workloads:
  - id: dhrystone
    workload_name: dhrystone
    iterations: 1

Required YAML entries for gem5

gem5_args
Specify the simulation to be run. This should be the same as you would specify for a stand-alone gem5 run.
gem5_vio_args
This parameter enables the virtio device in the simulated system. As a minimal requirement you need to ensure that the root parameter of the virtio device is exposed to the command line. Please set this to ‘{}’ in the agenda as it will later be set to the used directory by WA.

Optional YAML entries

gem5_binary
Specify which gem5 to execute. This option is useful for executing gem5 in a non-standard location, or in debug mode.
temp_dir
Temporary directory used for file transferring into gem5. This directory will be created and removed by WA.
checkpoint
When this is set to ‘True’, WA creates a checkpoint once the system is booted. This checkpoint can then later be used by WA to avoid boot time.
run_delay
This parameter sets the time that the system should sleep prior to running workloads or taking checkpoints.
username
This is a Linux-specific parameter, as most Linux systems require a login. If a login prompt is found, this field will be used as username.
password
As above, but for passwords


Patch for the gem5 simulator

The patch below is required to complete the integration with gem5. It adds a VirtIO device to the default full-system simulation script, and exposes it via an argument to the script. 

diff --git a/configs/common/Options.py b/configs/common/Options.py
--- a/configs/common/Options.py
+++ b/configs/common/Options.py
@@ -351,3 +351,8 @@
     parser.add_option("--command-line-file", action="store",
                       default=None, type="string",
                       help="File with a template for the kernel command line")
+
+    # Workload Automation options
+    parser.add_option("--workload-automation-vio", action="store", type="string",
+                      default=None, help="Enable the Virtio 9P device and set "
+                      "the path to use. Required to use Workload Automation")
diff --git a/configs/example/fs.py b/configs/example/fs.py
--- a/configs/example/fs.py
+++ b/configs/example/fs.py
@@ -225,6 +225,25 @@
             not options.fast_forward:
             CpuConfig.config_etrace(TestCPUClass, test_sys.cpu, options)

+        if buildEnv['TARGET_ISA'] != "arm" and options.workload_automation_vio:
+            warn("Ignoring --workload-automation-vio. It is unsupported on "
+                 "non-ARM systems.")
+        else:
+            from m5.objects import PciVirtIO, VirtIO9PDiod
+            viopci = PciVirtIO(pci_bus=0, pci_dev=test_sys.realview._num_pci_dev,
+                               pci_func=0, InterruptPin=1,
+                               InterruptLine=test_sys.realview._num_pci_int_line)
+
+            test_sys.realview._num_pci_dev = test_sys.realview._num_pci_dev + 1
+            test_sys.realview._num_pci_int_line = test_sys.realview._num_pci_int_line + 1
+
+            viopci.vio = VirtIO9PDiod()
+            viopci.vio.root = options.workload_automation_vio
+
+            test_sys.realview.viopci = viopci
+            test_sys.realview.viopci.dma = test_sys.iobus.slave
+            test_sys.realview.viopci.pio = test_sys.iobus.master
+
         CacheConfig.config_cache(options, test_sys)

         MemConfig.config_mem(options, test_sys)
diff --git a/src/dev/arm/RealView.py b/src/dev/arm/RealView.py
--- a/src/dev/arm/RealView.py
+++ b/src/dev/arm/RealView.py
@@ -270,6 +270,8 @@
     cxx_header = "dev/arm/realview.hh"
     system = Param.System(Parent.any, "system")
     _mem_regions = [(Addr(0), Addr('256MB'))]
+    _num_pci_dev = 0
+    _num_pci_int_line = 0

     def _on_chip_devices(self):
         return []
@@ -615,10 +617,18 @@

     # Attach any PCI devices that are supported
     def attachPciDevices(self):
-        self.ethernet = IGbE_e1000(pci_bus=0, pci_dev=0, pci_func=0,
-                                   InterruptLine=1, InterruptPin=1)
-        self.ide = IdeController(disks = [], pci_bus=0, pci_dev=1, pci_func=0,
-                                 InterruptLine=2, InterruptPin=2)
+        self.ethernet = IGbE_e1000(pci_bus=0, pci_dev=self._num_pci_dev,
+                                   pci_func=0,
+                                   InterruptLine=self._num_pci_int_line,
+                                   InterruptPin=1)
+        self._num_pci_dev = self._num_pci_dev + 1
+        self._num_pci_int_line = self._num_pci_int_line + 1
+        self.ide = IdeController(disks = [], pci_bus=0,
+                                 pci_dev=self._num_pci_dev, pci_func=0,
+                                 InterruptLine=self._num_pci_int_line,
+                                 InterruptPin=2)
+        self._num_pci_dev = self._num_pci_dev + 1
+        self._num_pci_int_line = self._num_pci_int_line + 1

     def enableMSIX(self):
         self.gic = Pl390(dist_addr=0x2C001000, cpu_addr=0x2C002000, it_lines=512)
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