KVM - User contributions [en]

KVMClock

2010-09-29T18:02:05Z

Glommer:

= KVM PVclock =

Linux guests only.

== Testing ==

You can verify kvm-clock is enable by checking

/sys/devices/system/clocksource/clocksource0/current_clocksource

Output should say "kvm-clock"

Some basic mechanism to make sure it works:

* Try guests without kvm-clock too. Make sure they at least boot
* make sure successive gettimeofday calls never go backwards (testing this can take days)
* make sure that calls to different time sources (like gettimeofday and monotonic) do not deviate too much, nor go backwards.

=== Note ===

Older Linux guests with backported versions of kvmclock may need different ways to check for kvmclock. This is due to the fact that those guests might lack total support for the clocksource subsystem

* RHEL/CentOS 5.x: for the x86_64 version, the "current_clocksource" file exists, but will always return "jiffies", no matter what. One should search for "KVM" in dmesg | grep time.c

KVM Features

2010-01-21T18:12:34Z

Glommer:

= KVM-Features =

This is a possibly incomplete list of KVM features, together with their status. Feel free to update any of them as you see fit.

As a guideline, there is a feature description template in [[FeatureDescription/Template|here]]

* [[MonitorProtocol|QMP]] - Qemu Monitor Protocol
* [[KSM|KSM]] - Kernel Samepage Merging
* [[KVMClock|Kvm Paravirtual Clock]] - A Paravirtual timesource for KVM
* [[CPUHotPlug|CPU Hotplug support]] - Adding cpus on the fly
* [[pcihotplug|PCI Hotplug support]] - Adding pci devices on the fly
* [[VMchannel_Requirements | vmchannel ]] - Communication channel between the host and guests
* [[migration]] - Migrating Virtual Machines
* [[vhost]] -
* [[scsi|SCSI disk emulation]] -
* [[virtio|Virtio Devices]] -
* [[CPU clustering]] -
* [[hpet]] -
* [[device assignment]] -
* [[pxe boot]] -
* [[iscsi boot]] -
* [[x2apic]] -
* [[floppy]] -
* [[cdrom]] -
* [[usb]] -
* [[UsbPassThrouhg|Usb host devices passthrough]] -
* [[sound]] -
* [[UserspaceIrqchip|Userspace Irqchip emulation]] -
* [[UserspacePit|Userspace Pit emulation]] -
* [[Balloon|Balloon memory driver]] -
* [[LargePages|Large pages support]] -
* [[StableABI|Stable Guest ABI]] -

KVM Features

2010-01-20T13:38:15Z

Glommer:

= KVM-Features =

This is a possibly incomplete list of KVM features, together with their status. Feel free to update any of them as you see fit.

As a guideline, there is a feature description template in [[FeatureDescription/Template|here]]

* [[MonitorProtocol|QMP]] - Qemu Monitor Protocol
* [[KSM|KSM]] - Kernel Samepage Merging
* [[KVMClock|Kvm Paravirtual Clock]] - A Paravirtual timesource for KVM
* [[CPUHotPlug|CPU Hotplug support]] - Adding cpus on the fly
* [[pcihotplug|PCI Hotplug support]] - Adding pci devices on the fly
* [[vmchannel]] -
* [[migration]] - Migrating Virtual Machines
* [[vhost]] -
* [[scsi|SCSI disk emulation]] -
* [[virtio|Virtio Devices]] -
* [[CPU clustering]] -
* [[hpet]] -
* [[device assignment]] -
* [[pxe boot]] -
* [[iscsi boot]] -
* [[x2apic]] -
* [[floppy]] -
* [[cdrom]] -
* [[usb]] -
* [[UsbPassThrouhg|Usb host devices passthrough]] -
* [[sound]] -
* [[UserspaceIrqchip|Userspace Irqchip emulation]] -
* [[UserspacePit|Userspace Pit emulation]] -
* [[Balloon|Balloon memory driver]] -
* [[LargePages|Large pages support]] -

KVM Features

2010-01-20T13:28:20Z

Glommer:

= KVM-Features =

This is a possibly incomplete list of KVM features, together with their status. Feel free to update any of them as you see fit.

As a guideline, there is a feature description template in [[FeatureDescription/Template|here]]

* [[MonitorProtocol|QMP]] - Qemu Monitor Protocol
* [[KSM|KSM]] - Kernel Samepage Merging
* [[KVMClock|Kvm Paravirtual Clock]] - A Paravirtual timesource for KVM
* [[CPUHotPlug|CPU Hotplug support]] - Adding cpus on the fly
* [[pcihotplug|PCI Hotplug support]] - Adding pci devices on the fly
* [[vmchannel]] -
* [[migration]] - Migrating Virtual Machines
* [[vhost]] -
* [[CPU clustering]] -
* [[hpet]] -
* [[device assignment]] -
* [[pxe boot]] -
* [[iscsi boot]] -
* [[x2apic]] -
* [[floppy]] -
* [[cdrom]] -
* [[usb]] -
* [[UsbPassThrouhg|Usb host devices passthrough]] -
* [[sound]] -
* [[UserspaceIrqchip|Userspace Irqchip emulation]] -
* [[UserspacePit|Userspace Pit emulation]] -
* [[Balloon|Balloon memory driver]] -
* [[LargePages|Large pages support]] -

KVM Features

2010-01-20T13:09:07Z

Glommer:

KVM Features

2010-01-19T17:47:42Z

Glommer:

KVM Features

2010-01-19T13:49:36Z

Glommer:

= KVM-Features =

This is a possibly incomplete list of KVM features, together with their status. Feel free to update any of them as you see fit.

* [[MonitorProtocol|QMP]] - Qemu Monitor Protocol
* [[KSM|KSM]] - Kernel Samepage Merging
* [[KVMClock|Kvm Paravirtual Clock]] - A Paravirtual timesource for KVM
* [[CPUHotPlug|CPU Hotplug support]] - Adding cpus on the fly
* [[vmchannel]] -
* [[migration]] - Migrating Virtual Machines
* [[vhost]] -
* [[CPU clustering]] -
* [[hpet]] -
* [[device assignment]] -
* [[pxe boot]] -
* [[iscsi boot]] -
* [[x2apic]] -

KVMClock

2010-01-19T13:42:18Z

Glommer:

KVM Features

2010-01-19T13:36:50Z

Glommer:

CPUHotPlug

2010-01-19T13:30:39Z

Glommer:

= CPU Hotplug =

CPU hotplug is a controverse feature. It exists on qemu-kvm for
some time now, and according to some BZ movement, we know there are users for
it. There are very few physical machines that actually support it. (Only one
unisys box I know of), The Linux implementation follows what this specific
box do, but happens to break Windows SVVP tests in an appearently unsolvable
way. No one knows how to implement it on Windows, but it is believed that
it should involve a windows-specific driver (to be written)

Hot-unplug does not work, and actually, does not even make that much sense.

== Status ==

Linux guest support is pretty old, dating back to something around 2.6.19. qemu-kvm support exists, but merging it into qemu.git was not successful when tried, in the past. Reason being the BIOS changes, for the reasons already mentioned.

== Testing ==

In any case, here's how to verify it:

* switch to the monitor
* type cpu_set <n+1> on
* A new cpu should appear on /sys/devices/system/cpu
* bring it online by writting 1 to the "online" file inside that directory
* Try adding as many cpus as possible, and make sure we at least do not crash.

KSM

2010-01-19T13:22:47Z

Glommer:

= Kernel Samepage Merging =

KSM is a memory-saving de-duplication feature, that merges anonymous (private) pages (not pagecache ones). Although it started this way, KSM is currently not suitable only for Virtual Machine use, but rather, it can be useful to any
application which generates many instances of the same data

== Enabling KSM ==

KSM only operates on those areas of address space which an application
has advised to be likely candidates for merging, by using the madvise(2)
system call: int madvise(addr, length, MADV_MERGEABLE).

The app may call int madvise(addr, length, MADV_UNMERGEABLE) to cancel
that advice and restore unshared pages: whereupon KSM unmerges whatever
it merged in that range. Note: this unmerging call may suddenly require
more memory than is available - possibly failing with EAGAIN, but more
probably arousing the Out-Of-Memory killer.

== Status ==

Merged in linux 2.6.32. One needs to enable it via CONFIG_KSM=y

== Results ==

TBD

== Testing ==

You can verify KSM is in action, by checking for the existence of some of its /sys files, under /sys/kernel/mm/ksm/

They are:

{|
|-
|pages_shared
|how many shared pages are being used
|-
|pages_sharing
|how many more sites are sharing them i.e. how much saved
|-
|pages_unshared
|how many pages unique but repeatedly checked for merging
|-
|pages_volatile
|how many pages changing too fast to be placed in a tree
|-
|full_scans
|how many times all mergeable areas have been scanned
|-
|}

KVM Features

2010-01-19T13:04:56Z

Glommer:

Main Page

2010-01-19T12:52:32Z

Glommer:

== Kernel Based Virtual Machine ==

KVM (for Kernel-based Virtual Machine) is a full virtualization solution for Linux on x86 hardware containing virtualization extensions (Intel VT or AMD-V). It consists of a loadable kernel module, kvm.ko, that provides the core virtualization infrastructure and a processor specific module, kvm-intel.ko or kvm-amd.ko. KVM also requires a modified QEMU although work is underway to get the required changes upstream.

Using KVM, one can run multiple virtual machines running unmodified Linux or Windows images. Each virtual machine has private virtualized hardware: a network card, disk, graphics adapter, etc.

The kernel component of KVM is included in mainline Linux, as of 2.6.20.

KVM is open source software.

== Common Pages ==
{| style="border:none"
|style="width:50%;border:none;"|
* [[KVM Forum]]
* [[TODO]]
* [[KVM-Autotest]]
* [[KVM Features]]
|style="width:50%;border:none;"|
* [[Management Tools]]
* [[Documents]]
|}

== Common External Pages ==
{|style="border:none"
|style="width:50%;border:none;"|
* [http://www.nongnu.org/qemu QEMU]
* [http://wiki.xensource.com/xenwiki/HVM_Compatible_Processors Xen's HVM Compatible Processors List]
|style="width:50%;border:none;"|

* [http://qemu-buch.de Wikibook "QEMU & KVM"]
* [http://qemu-buch.de/cgi-bin/moin.cgi/ QEMU Wiki]
|}