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In this slide deck on Xen vs KVM, the benchmarks indicate that CPU and disk is nearly as fast under virtualization (~10% slowdown). Yet virtualization slows down a kernel compile by more than a factor of 2. What causes this?
A Linux kernel compile is a process heavy operation (lots of short-lived processes). Process creation/destruction involves setting up and tearing down MMU state. MMU virtualization is expensive (especially in software). There is a VMware whitepaper that shows the improvement in compile-time benchmarks when hardware MMU virtualization is used. I don't think the hardware used in the referenced slide provides hardware MMU virtualization. I don't know if either KVM or Xen support it (but I suspect so).
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I have use vmware. I define 5 gb ram for it.
When look system resources in task manager I see vmware just uses 20 mb.
But when I look in vmware (centos) it uses 2gb ram.
How can I see the real usage?
thanks in advance
Try this link:
http://www.vmware.com/content/dam/digitalmarketing/vmware/en/pdf/techpaper/perf-vsphere-memory_management.pdf
It says here:
In order to quickly monitor virtual machine memory usage, the VMware
vSphere™ Client exposes two memory statistics in the resource
summary:
Consumed Host Memory
Active Guest Memory
Consumed Host Memory usage is defined as the amount of host memory
that is allocated to the virtual machine, Active Guest Memory is
defined as the amount of guest memory that is currently being used by
the guest operating system and its applications.
A lot of other information in the article.
Hope this helps.
_Vamsi
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I recently had to enable VT for windows7 since I want to run ubuntu on vmware so I was wondering why isnt it enabled by default is it some kind of security issue or just not necessary for the average user?
There are several reasons, including "security" and "performance":
https://superuser.com/questions/291340/why-do-pc-manufacturers-disable-advanced-cpu-features-in-the-bios-by-default
http://www.vmware.com/pdf/asplos235_adams.pdf
Intel virtualization technology can get hardware intensive and although the software requirement is low (Windows Vista) only modern CPUs made by INTEL ONLY such as Intel i7 support it.
Not all windows computers have an Intel CPU though (a good amount of them do). The only people that use the VTX technology are developers and people who want to run a different operating system than their computer came with, so not everyone. As for security issue, I'm not sure but it can get very RAM intensive. (i.e. the Android HAXM for developers has a default RAM usage of 2GB, and the minimum is 512 MB!).
If you want to know more you can check out this article
or the website:
http://www.intel.com/content/www/us/en/virtualization/virtualization-technology/intel-virtualization-technology.html
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Does anyone know if this chip is 32-bit or 64-bit? I would like to know before I decide to purchase one of these boards for development.
According to the Microprocessor Report on Adapteva (PDF):
The design also eschews memory management of any kind, implementing a
flat 32-bit memory space without any protection
and also
The instruction set supports load and store double instructions that
access two consecutive 32-bit registers, taking advantage of the
64-bit path from the SRAM to the register file.
So it sounds like a 32-bit computer than can do some 64-bit operations.
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I should write a study, comparing two operating systems. My choice was OS X and Ubuntu, especially because the last Ubuntu, 11.11 (Oneiric Ocelot) seems to be as OS X Lion.
This two themes are too large - I would like to be more specific in my study - such as kernel or thread differences. Can you suggest me some ideas, which are large enough to write a study about them, but specifically good enough in the same time?
Thanks.
Some ideas to investigate:
license and freedom of software (and of user data).
the /proc filesystem
kernel limitations (number of threads, of processes, of inodes, max file sizes)
availability of cross platform framework libraries (like Qt)
hardware drivers & heterogeneity
thread implementations
dynamic libraries, plugins
graphical interfaces
availability of language implementations
etc etc
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My VPS provider gives me the choice between KVM and OpenVZ. What is the best choice for a VPS with 128MB or 256MB RAM?
KVM does not provide anywhere near the performance of OpenVZ (or Virtuozzo, its commercial equivalent). It's extremely important to note that KVM requires a running kernel inside the VPS, whereas OpenVZ runs containers using a shared kernel. This means that a 256MB KVM VPS does not actually have the same amount of memory available to userspace that OpenVZ does. OpenVZ is an extremely lightweight virtualization technology that easily outperforms full virtualization.
KVM does provide better isolation, although this isn't usually apparent to userspace in a container.
As for the original question, if I were shopping for a VPS, there are two factors to consider:
1) At the same price point, you'll get less for your money with KVM. 256MB of KVM is less than 256MB of OpenVZ because you have to run your own kernel so there's less for your actual applications. On the other hand, some hosters charge more for OpenVZ, so you'll need to do the math.
2) It's easier for hosting companies to overcommit OpenVZ systems, so bad hosting companies may put you on a system with too many containers, so be wary of this.
KVM has much better isolation than OpenVZ and in my experience KVM gets better performance as well. However I've heard some say they get better performance from OpenVZ. KVM has come a long way in the past year though, so I wouldn't be surprised if it's surpassed OpenVZ by now...
KVM also supports any operating system (in theory), whereas OpenVZ is limited to Linux only.
We're using KVM exclusively for our virtualization systems and have no interest in switching to anything else.
If your buying from a VPS provider, then KVM/Xen. OpenVZ/LXC suppliers can oversell their products.
If it's your own server then you can have a mix of OpenVZ/LXC and KVM on the same machine.
Choose KVM because OpenVZ is often cheaper to others hosts :)
OpenVZ does not give your processes the full amount of allocated memory due to overhead, so for smaller memory VPSes, I would lean towards choosing KVM or XEN.