Does kvm have out of order execution feature? if not can we implement to increase virtual machine performance or underlying processor will take care of it.
If the question is whether QEMU-KVM emulate OOO, then no they don't. QEMU can emulate an instruction set architecture (so you could run ARM code on x86, for example) but not at the level of instruction re-ordering. And it probably would only add extra overhead to do this in software.
On the other hand, if you run native code inside a VM (x86 binary on x86, but virtualized), then all unprivileged instructions are executed exactly as they would on a bare-metal. So if your CPU can execute out-of-order it will do so also for the code of your VM. The way the privileged processor instructions are executed depends on whether you are using KVM module alongside the QEMU. You can read more about this here or in more details here.
If you think your QEMU is too slow, check whether the KVM module is used: append the command line with by supplying the -enable-kvm argument. Also make sure your processor has virtualization support.
Also check this answer
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I have a QorIQ (P2041) processor based IoT device firmware. I have uBoot, Kernel and initrd ramdisk. Whatever I do with qemu-system-ppc I can't get it to work. I suspect that qemu-system-ppc doesn't support QorIQ processors. Is there anyway for me to load and boot this firmware in Qemu or any other emulator?
U-Boot has configuration file qemu-ppce500_defconfig. You should be able to run the U-Boot built with this configuration using command
qemu-system-ppc -nographic -bios u-boot -M ppce500
The CPU can be specified via the -cpu parameter as e500mc.
To run your kernel it will need drivers for the hardware provided by the emulated machine like the E1000 network card and the NS16550 console.
Use the fdt command of U-Boot to get an overview of the available devices in the emulated machine.
Firmware binaries are generally very closely tied to the hardware they're built to run on -- they make assumptions about what hardware is available, what addresses in memory it can be found at, and so on. You need to use a firmware blob that corresponds to the hardware you're asking QEMU to emulate. Since QEMU doesn't emulate whatever your random IoT device is, you need to use a u-boot which matches the hardware QEMU actually has (as for example suggested in Xypron's answer).
Once you have booting firmware, you will likely still find you have exactly the same problem with the kernel -- it is built to run on one bit of hardware, and you're trying to run it on something different, and this simply won't work.
I understand that QEMU built-in gdbserver can be used to debug kernel or bare-metal program. But I am curious that if it is possible to use QEMU built-in gdbserver to debug a program running in guest os in QEMU.
It is possible, but it won't be pleasant. Don't be surprised if execution bounces around as the kernel services external interrupts, and switches to other tasks. I'd recommend using a normal user-mode debugger inside the VM if possible.
When I build an executable using nvcc, I can, by default, profile it using nvprof or Nvidia visual profiler GUI. My concern is that, even when I am not actually profiling it, my executable may not be running optimally, because it is 'able' to record or emit information about profiling. So, I am feeling like by default, executables are built with profiling enabled.
Strange that this question was not asked before, the answer is not obvious to me. Is there a compiler option to disable profiling, especially for release mode? Or is profiling completely free?
Is there a compiler option to disable profiling, especially for release mode? Or is profiling completely free?
There is no compiler option to disable profiling. It is completely free.
I'm writing a program that manages data entered by users. I plan to open a test version to the public and have no idea how many users there may be.
I want my program to test when memory is getting low so that I know when to buy more server space and so that I can automatically restrict data entry when necessary. What's a good way to detect memory shortage? Allocate garbage space temporarily to get the exception? Is there a better way?
This may be best accomplished outside of your application using a performance monitoring tool. Windows Server can be configured to do this for you; see this question. There are other tools out there that help you monitor your servers, and I advise you to use an existing system unless you absolutely have to do this with Python.
If you must absolutely do this using Python, then have a look at the psutil library:
psutil (python system and process utilities) is a cross-platform
library for retrieving information on running processes and system
utilization (CPU, memory, disks, network) in Python. It is useful
mainly for system monitoring, profiling and limiting process resources
and management of running processes. It implements many
functionalities offered by command line tools such as: ps, top, lsof,
netstat, ifconfig, who, df, kill, free, nice, ionice, iostat, iotop,
uptime, pidof, tty, taskset, pmap. It currently supports Linux,
Windows, OSX, FreeBSD and Sun Solaris, both 32-bit and 64-bit
architectures, with Python versions from 2.4 to 3.4. Pypi is also
known to work.
You may combine this with the email package to send the alerts.
I am a fresh man in kvm,qemu-kvm and kvm are both very complicated now.
Anyone can introduce some primers about qemu-kvm and kvm?
thanks very much!
KVM stands for kernel based virtual machine. it enables you to create as many number of virtual machine as you like. These machine can be of two types LVM based or Non-LVM based.
Those machine which are LVM based you can take live backup for them. for non-lvm based VM you cannot take live backup i.e. they will be paused when you take backup for them. please refer KVM home page KVM Home Page.
QEMU is a generic and open source machine emulator and virtualizer.When used as a machine emulator, QEMU can run OSes and programs made for one machine (e.g. an ARM board) on a different machine (e.g. your own PC). By using dynamic translation, it achieves very good performance. When used as a virtualizer, QEMU achieves near native performances by executing the guest code directly on the host CPU. QEMU supports virtualization when executing under the Xen hypervisor or using the KVM kernel module in Linux. When using KVM, QEMU can virtualize x86, server and embedded PowerPC, and S390 guests.
For managing the KVM VM's you need to install Libvirt which is the virtualization library. It provides you the tools for starting, suspending, resuming, cloning, restarting, listing of virtual machine. Please refer Libvirt home page for more reference.
If you are working on some backup or recovery process then I suggest you to go through this excellent perl script as well it will give a fair idea of how the backup and snapshot is being taken for KVM VM's.
KVM based virtual machines are not complicated once you go through the theory of them and start implementing them. I believe once you start working on them you will find fun in managing them.
Putting in a nutshell
QEMU : An emulator which translates the instruction of guest operating system to host operating system. As you can guess that translation has a certain cost, you will not see Guest machine working as fast as host machine.
For more info see the QEMU wiki
KVM (Kernal Virtual Machine): A module in Kernel which support Virtual Machine (host operating system) in hardware. By support I mean that if your guest architecture is same as host architecture, then certainly there is no need to translate the instructions as they can directly be executed by host. For this modern hardware are equipped with special registers and storage location which is leveraged by KVM. Also KVM is a module, some driver is needed to use the KVM, which is qemu also.
For more info see the KVM section in the same wiki.
QEMU-KVM : As I above mentioned, KVM is a module only, qemu is needed (or other) to use KVM. When KVM is used with QEMU, control transfers from QEMU to KVM and vice-versa over the execution.
Talking about KVM is talking about virtualization technology or about kernel modules (kvm.ko, kvm-intel.ko or kvm-amd-ko). Sometimes KVM is mentioned as a virtual machine, this is not correct, because KVM does not provide virtualized hardware.
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