XenTerminology: Difference between revisions
From Xen
				
				
				Jump to navigationJump to search
				
				 (Created page with "<!-- MoinMoin name:  XenTerminology --> <!-- Comment:         --> <!-- WikiMedia name: XenTerminology --> <!-- Page revision:  00000011 --> <!-- Original date:  Thu Apr 27 20:50:…")  | 
				Lars.kurth (talk | contribs)  mNo edit summary  | 
				||
| Line 72: | Line 72: | ||
[[Category:Beginners]]  | 
  [[Category:Beginners]]  | 
||
[[Category:Developers]]  | 
  [[Category:Developers]]  | 
||
[[Category:Paravirtualised Architecture]]  | 
|||
Revision as of 10:55, 24 June 2013
Xen Terminology
To add a definition, please provide a 1- or 2-line explanation, followed by a link to more details (other wiki pages, external web pages, etc) when available.
Basics
- guest operating system: An operating system that can run within the Xen environment.
 - hypervisor: Code running at a higher privilege level than the supervisor code of its guest operating systems.
 - virtual machine monitor ("vmm"): In this context, the hypervisor.
 - domain: A running virtual machine within which a guest OS executes.
 - domain0 ("dom0"): The first domain, automatically started at boot time. Dom0 has permission to control all hardware on the system, and is used to manage the hypervisor and the other domains.
 - unprivileged domain ("domU"): A domain with no special hardware access.
 
Approaches to Virtualization
- full virtualization: An approach to virtualization which requires no modifications to the hosted operating system, providing the illusion of a complete system of real hardware devices.
 - paravirtualization: An approach to virtualization which requires modifications to the operating system in order to run in a virtual machine. Xen uses paravirtualization but preserves binary compatibility for user space applications.
 
Address Spaces
- MFN (machine frame number): Real host machine address; the addresses the processor understands.
 - GPFN (guest pseudo-physical frame number): Guests run in an illusory contiguous physical address space, which is probably not contiguous in the machine address space.
 - GMFN (guest machine frame number): Equivalent to GPFN for an auto-translated guest, and equivalent to MFN for normal paravirtualised guests. It represents what the guest thinks are MFNs.
 - PFN (physical frame number): A catch-all for any kind of frame number. "Physical" here can mean guest-physical, machine-physical or guest-machine-physical.
 
Page Tables
- l4 table: Define me.
 - l3 table: Define me.
 - l2 table: Define me.
 - l1 table: Define me.
 - SPT (shadow page table): shadow version of a guest OSes page table. Useful for numerous things, for instance in tracking dirty pages during live migration.
 - PAE: Intel's Physical Addressing Extensions, which enable x86/32 machines to address up to 64 GB of physical memory.
 - PSE (page size extension): used as a flag to indicate that a given page is ahuge/super page (2/4 MB instead of 4KB).
 
Shadow Page Table Modes
- external: Define me.
 - translate: Define me.
 
x86 Architecture
- HVM: Hardware Virtual Machine, which is the full-virtualization mode supported by Xen. This mode requires hardware support, e.g. Intel's Virtualization Technology (VT) and AMD's Pacifica technology.
 - SVM: full-virtualization support on AMD's Pacifica-enabled processors
 - VT-x: full-virtualization support on Intel's x86 VT-enabled processors
 - VT-i: full-virtualization support on Intel's IA-64 VT-enabled processors
 - shadow mode: Define me.
 - writable page tables: Define me.
 
Networking Infrastructure
- backend: one half of a communication end point - interdomain communication is implemented using a frontend and backend device model interacting via event channels.
 - frontend: the device as presented to the guest; other half of the communication endpoint.
 - vif: virtual interface; the name of the network backend device connected by an event channel to a network front end on the guest.
 - event channel: Define me.
 - vethN: local networking front end on dom0; renamed to ethN by xen network scripts in bridging mode (FIXME)
 - pethN: real physical device (after renaming)
 
Migration
- Live migration: A technique for moving a running virtual machine to another physical host, without stopping it or the services running on it.
 
Scheduling
- BVT: The Borrowed Virtual Time scheduler is used to give proportional fair shares of the CPU to domains.
 - SEDF: The Simple Earliest Deadline First scheduler provides weighted CPU sharing in an intuitive way and uses realtime algorithms to ensure time guarantees.
 
