The VMP add-on for Simics makes use of hardware virtualization support to provide vastly improved performance when simulating x86-based systems. It is an optional part of the x86-based models.
The VMP feature requires that the host machine running Simics has the Intel® Virtualization Technology (Intel® VT) for IA-32, Intel® 64 and Intel® Architecture (Intel® VT-x) enabled in the host machine firmware (the BIOS).
Almost all Intel® processors since the original Core™ architecture, including Xeon® server processors, support the Intel® VT-x feature set. See the Intel® ARK at ark.intel.com for information on specific products.
The Intel® VT-x virtualization feature and the NX execute protection feature must also be enabled in the host machine firmware to run VMP. Look for options under either Security or Virtualization to find where to enable Intel® VT and NX in your firmware. If Intel® Trusted Execution Technology (TXT) is enabled in the firmware, it can also happen that the Intel® VT-x virtualization feature is restricted to trusted applications only; there is usually a special firmware setting controlling this behavior. VMP requires Intel® VT-x to be generally available.
All major features of Simics, including full inspectability of simulated state, ability to model heterogeneous systems, and reverse execution, are fully supported when running with VMP.
Installing and managing VMP kernel modules requires sudo
privileges. Installing will compile the kernel module and therefore
also requires an environment to build kernel modules. Which packages
you need for building kernel modules depend on the distribution of
Linux that you are using, but at least for certain Red Hat based
distributions you would
need gcc-c++, kernel-headers,
and kernel-devel. Change directory to the Simics Base package
and run:
joe@computer$ bin/vmp-kernel-install
The script will compile and persistently install the kernel modules
that are used by VMP. It will echo what needs to be done, which
involves running scripts in the vmxmon/scripts/
directory.
Disable VMP temporarily by running
the bin/vmp-kernel-unload script, and enable VMP with
the bin/vmp-kernel-load script. Permanently uninstall VMP
from your host by running the bin/vmp-kernel-uninstall
script.
If your installation is read-only, or you for some other reason want to have the built VMP artifacts outside of the installation, you can give a directory to the relevant VMP scripts, example:
joe@computer$ bin/vmp-kernel-install /somewhere/directory joe@computer$ bin/vmp-kernel-load /somewhere/directory
The kernel module can be loaded and unloaded by running
the bin\vmp-kernel-load.bat
respective bin\vmp-kernel-unload.bat scripts as
administrator. To do that, open a command shell as administrator and run:
bin\vmp-kernel-load.bat
Another way to perform the same action would be to right-click on
vmp-kernel-load.bat and select run as administrator.
The /AUTO and /DEMAND options select the start option for the VMP service. With /AUTO (default), the service will be available after restart whereas with /DEMAND (which used to be the behavior before these flags were added) will mean that the service is only available until shutdown or reboot and then has to be manually loaded again if needed.
If the script fails, see the Windows event log for more information. The most common reason is that Intel® VT-x technology or the NX feature is not enabled in the BIOS. The kernel module will also fail to load if Windows is running with the Hyper-V feature enabled.
Windows 8 and later can be run with Hyper-V enabled. Hyper-V is a feature where the operating system is run as a guest under the control of a hypervisor. VMP cannot be used in conjunction with Hyper-V: loading the VMP kernel module will fail.
There are various ways to disable the Hyper-V feature. Below are instructions for adding an additional boot configuration database entry to make it easy to boot with Hyper-V disabled:
bcdedit /copy {current} /d "Win 8.1 with Hyper-V disabled"
This will print the id of the newly created entry, e.g.
The entry was successfully copied to {41f7b750-485b-4f02-9d0e-4c8e3d02c31d}.
bcdedit /set {41f7b750-485b-4f02-9d0e-4c8e3d02c31d} hypervisorlaunchtype off
With the VMP kernel modules installed, VMP will be enabled by default for each processor. You can disable VMP by running the disable-vmp command.
Due to details about how the Intel® VT feature that VMP is based on works, the acceleration may not kick in. Use the system-perfmeter to find out if a processor actually uses the VMP execution mode. To find out why VMP is not used, either raise the log level of the CPU in question or use the info command on the CPU.
The VMP packages are currently available and supported for Linux and Windows.
VMP is designed to be a transparent performance enhancement. The implementation with Intel® VT-x makes that impossible in some areas, and in some other areas we have taken the chance to utilize the VMP mode to tweak performance further. Enabling features that cannot be emulated using Intel® VT-x will automatically disable VMP.
VMP is optimized for software development, and the default timing parameters used in VMP reflect that. The timing settings can be viewed with the info command on the CPU object. As default, VMP timing will stall the PAUSE instruction, the RDTSC instruction, and each port-mapped I/O access for 10 milliseconds. These stalls are added to allow loops containing these operations to consume more virtual time per iteration and therefore speed up simulation if the loop is terminated after a set virtual time. This is controlled by attributes in the CPU object and can be changed if somewhat more realistic timing is more important than maximum simulation speed.
The hardware performance counters are used to figure out the number of executed instructions when running in VMP mode. Since those counters count string instructions as one regardless of the number of iterations, this is the instruction count model that must be used to enable VMP. This is controlled by the one_step_per_string_instruction attribute, and setting that to classic counting will disable VMP.
The TLB model is bypassed in VMP mode. To simulate a particular configuration of the TLB, or listen to the haps that the TLB model generates, VMP has to be manually disabled.