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Topic: Paravirtualization

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	Paravirtualization - Wikipedia, the free encyclopedia
		In computing, paravirtualization is a virtualization technique that presents a software interface to virtual machines that is similar but not identical to that of the underlying hardware.
		This requires operating systems to be explicitly ported to run on top of the virtual machine monitor (VMM) but may enable the VMM itself to be simpler and for the virtual machines that run on it to achieve higher performance.
		The term "paravirtualization" was first used in the research literature in association with the Denali virtual machine monitor.
	en.wikipedia.org /wiki/Paravirtualization (258 words)

	Virtualization Blog
		Paravirtualization (as an approach to run virtual machines) has been getting a lot of attention lately.
		Paravirtualization (an idea orginally introduced by the Denali Project) proposes to modify a guest OS in order to redirect virtualization sensitive operations directly to the virtual machine monitor instead of trapping to it as done in pure hardware virtualization.
		The issue with paravirtualization is that once you break the strict hardware interface between the hypervisor and the guest OS, one might as well call the "hypervisor" a microkernel and a guest OS a process and move on.
	www.virtualiron.com /fusetalk/blog (1945 words)

	Gimme Hardware/Software Interface.: Xen and RedHat
		Paravirtualization constrasts with the "fl-box" virtualization practiced by classical VMMs, wherein the OS is carefully kept unaware that the VMM exists, and the VMM in turn has little semantic knowledge about the OS.
		Having worked at VMware for a while when I first heard the term, paravirtualization initially struck me as a bit of a hack; i.e., it looks like a way to get some of the advantages of virtual machines, without having to solve some of the ludicrous problems that the x86 presents for classical VMMs.
		A paravirtualized VMM is simply a different point on this continuum, somewhere between the bare-metal VMM provided by something like VMware ESX Server, and the higher-level (though still pretty low-level) interface provided by an exokernel.
	x86vmm.blogspot.com /2005/11/xen-and-redhat.html (828 words)

	Xen - Wikipedia, the free encyclopedia
		This form of virtualization is achieved using a technique called paravirtualization.
		Xen uses a technique called paravirtualization to achieve high performance (i.e., low performance penalties, typically around 2%, with worst-case scenarios at 8% performance penalty).
		Through paravirtualization, it can achieve high performance even on its host architecture (x86) which is notoriously uncooperative with traditional virtualization techniques.
	en.wikipedia.org /wiki/Xen (1168 words)

	Hypervisor - Wikipedia, the free encyclopedia
		An alternative approach requires that the guest operating system be modified to make system calls to the hypervisor, rather than executing machine I/O instructions which are then simulated by the hypervisor.
		This is called paravirtualization in Xen, a "hypercall" in Parallels Workstation, and a "DIAGNOSE code" in IBM's VM.
		Xen is able to run both paravirtualized and, with the help of the hardware virtualization extensions Intel VTx, fully virtualized (i.e.
	en.wikipedia.org /wiki/Hypervisor (801 words)

	[RFC, PATCH 1/24] i386 Vmi documentation (Site not responding. Last check: 2007-11-02)
		If these + changes are visible to the guest OS in a paravirtualized system, + this will require updates to the guest kernel, which presents a + maintenance problem.
		Since the switch into paravirtual mode + may happen dynamically, the guest OS must not rely on testing for a + specific privilege level by checking the RPL field of segment + selectors, but should check for privileged execution by performing + an (RPL != 3 andand !EFLAGS_VM) comparison.
		It is + paravirtualized to remove the overhead implied by executing the native + delay.
	lists.osdl.org /pipermail/virtualization/2006-March/000313.html (11425 words)

	Transparent Paravirtualization And The Proposed Virtual Machine Interface (VMI)
		Paravirtualization is a slightly different approach to running virtual machines that is getting attention as of late (such as these news.com, linuxvirtualization.com, and theregister.com articles).
		In paravirtualization, a guest operating system is aware that it is running inside of a virtual machine.
		Based on this awareness, the paravirtualized guest operating system executes different code paths that typically make the job of virtualization easier and more efficient.
	www.thincomputing.net /newsitem1967.html (402 words)

	Xen - Server Virtualization with the Xen Hypervisor (Site not responding. Last check: 2007-11-02)
		XenSource was founded by the creators of paravirtualization, the acknowledged state of the art virtualization technology that allows hosted virtual servers to collaborate with the Xen hypervisor to achieve the best performance for enterprise applications, with a smaller code base, greater security and up to 10 times less overhead than alternative virtualization approaches.
		Paravirtualization requires a tiny hypervisor code base (Xen is under 50 KLOC) that results in extremely low performance overhead, typically in the range of 0.1% to 3.5% for industry standard performance benchmarks.
		Xen’s paravirtualized drivers run outside the core hypervisor, where they implement policy for resource sharing between multiple guests, providing fine-grained partitioning of I/O between multiple virtual servers.
	www.xensource.com /xen/xen/paravirtualization.html (320 words)

	virtualization.info: Virtual Iron rejects paravirtualization
		I strongly agree with this vision: the big problem of paravirtualization is that achieved performances are not a desirable benefit when you have to trade off them with kernel modification of your guest operating system.
		Hardly software house would agree to support their applications on a paravirtualized OS, for the simple reason the environment is not controlled anymore.
		Also, the biggest trade off point is that paravirtualization doesn't permit to run Microsoft Windows and, as I said many times, this is a limit big enough to prevent the technology from entering in the largest part of the market: the SMB segment.
	www.virtualization.info /2006/07/virtual-iron-rejects.html (1790 words)

	LKML: Zachary Amsden: VMI Interface Proposal Documentation for I386, Part 1
		The general approach to paravirtualization rather than full virtualization is to modify the guest operating system.
		In the course of development with a virtualized environment, it is not uncommon for support of new features or higher performance to require radical changes to the operation of the system.
		If these changes are visible to the guest OS in a paravirtualized system, this will require updates to the guest kernel, which presents a maintenance problem.
	lkml.org /lkml/2006/3/13/222 (827 words)

	NOVELL: Connection Magazine First Quarter 2006: Xen and the Art of Virtualization
		But there are some issues: certain operating system supervisor instructions must be handled by the VMM for correct virtualization, possibly resulting in a high performance cost for some operations such as creating a new application process.
		Paravirtualization avoids the performance drawbacks of full virtualization by offering a VM abstraction similar to, but not identical to, the underlying hardware.
		The general approach to paravirtualization requires that guest operating systems be modified prior to runtime.
	www.novell.com /connectionmagazine/2006/q1/trend_talk.html (1096 words)

	Introduction to virtualization - OpenVZ Wiki
		This technique also requires a VMM, but most of its work is performed in the guest OS code, which in turn is modified to support this VMM and avoid unnecessary use of privileged instructions.
		The paravirtualization technique also enables running different OSs on a single server, but requires them to be ported, i.e.
		The paravirtualization approach is used by products such as Xen and UML.
	wiki.openvz.org /Introduction_to_virtualization (457 words)

	2006 Linux Symposium --
		Paravirtualization has a lot of promise, in particular in its ability to deliver performance by allowing the hypervisor to be aware of the idioms in the operating system.
		Since Linux kernel changes are necessary, it is very easy to get into a situation where the paravirtualized kernel is incapable of executing on a native machine, or on another hypervisor.
		It is also quite easy to expose too many hypervisor'isms (in the name of performance), which can impede the general developement of the kernel with many hypervisor specific subtleties.
	www.linuxsymposium.org /2006/view_abstract.php?content_key=83 (236 words)

	LKML: Zachary Amsden: [RFC, PATCH 0/24] VMI i386 Linux virtualization interface proposal (Site not responding. Last check: 2007-11-02)
		Unlike the full-virtualization techniques used in the traditional VMware products, paravirtualization is a technique where the operating system is modified to enlighten the hypervisor with timely knowledge about the operating system's activities.
		Not surprisingly, paravirtualization's strength, ie that it encourages tighter communication between the kernel and the hypervisor, is also its weakness.
		Unless the changes to the operating system are moderated, you can very quickly find yourself with a kernel that (a) looks and feels like a brand new kernel or (b) cannot run on native machines or on newer versions of the hypervisor without a full recompile.
	lkml.org /lkml/2006/3/13/140 (910 words)

	Xen and Option-C
		In this document we focus upon Xen, one of the few virtualization packages to use “paravirtualization” to optimize system resource use.
		The wikipedia defines paravirtualization as "a virtualization technique that presents the abstraction of virtual machines with a software interface that is similar but not identical to that of the underlying hardware."
		Paravirtualization is more difficult to achieve because of the wide variety of hardware available.
	www.option-c.com /Xen.html (2027 words)

	Debunking Linus's Latest
		It is a general article for a general audience, and one should not confuse it for any sort of scholarly treatment of the area.
		Paravirtualization is an important idea, both in its own right and as a partial solution for reliability.
		The idea of adapting paravirtualization to a microkernel for use within an operating system is, frankly, silly.
	www.coyotos.org /docs/misc/linus-rebuttal.html (1485 words)

	CiteULike: Xen and the art of virtualization (Site not responding. Last check: 2007-11-02)
		But most previous work focused on "pure/complete" virtualization of the underlying hardware, while Xen uses the "paravirtualization" approach to expose a restricted view of the bare machine to boost performance.
		The Denali system also uses paravirtualization, but in Denali each virtual machine essentially hosts a single user, single application unprotected OS; while in Xen each domain is a full fledged OS by itself.
		The paper makes a compelling case for paravirtualized systems and the concept of being able to run 100 independent OS instances on a single computer seems fascinating.
	www.citeulike.org /user/diwakergupta/article/168648 (985 words)

	Mainframe: The Virtual Invasion
		For example, the IBM POWER4/POWER5's hypervisor paravirtualizes similar to Xen, in that it requires a modified client OS.
		Yes, I consider paravirtualization solutions like vPars and Xen to be hypervisors because they are simple fencing and translating mechanisms.
		Let's say that paravirtualization is something else, sometimes better.
	mainframe.typepad.com /blog/2005/11/the_virtual_inv.html (955 words)

	FRUUG : Xen, Paravirtualization, and Solaris
		At our April FRUUG meeting, Stu Maybee will talk talk about what is involved in preparing an operating system for execution in a paravirtualized hypervisor environment such as that provided by Xen.
		Given that Stu works at Sun Microsystems, and his favorite operating system is the Solaris OS, he'll talk about supporting it on Xen on x86-architecture platforms.
		April 20: Xen, Paravirtualization, and the Solaris OS, a joint meeting with the Front Range Open Solaris User Group (FROSUG).
	www.fruug.org /Archive/2006-04 (912 words)

	The Need for Virtualization and Xen > What Is Virtualization? (Site not responding. Last check: 2007-11-02)
		David Chisnall suggests virtualization and paravirtualization applications such as Xen, which is discussed in this article.
		A more efficient solution is provided by virtualization and paravirtualization applications such as Xen.
		The idea behind virtualization is an extension of that found in a modern operating system.
	www.quepublishing.com /articles/article.asp?p=459621 (887 words)

	FRUUG : Xen, Paravirtualization, and Solaris
		At our April, 2006 joint meeting with the Front Range Open Solaris Users Group, co-sponsored by the CU Computer Science Department, Stu Maybee of Sun Microsystems discussed the University of Cambridge's Xen hypervisor software.
		Stu discussed the distinction between hypervisors that provide full virtualization, where the OS doesn't know that its running in a virtual machine environment, and paravirtualization, where the operating system is modified to run in the virtual machine environment.
		With the operating system aware of the environment in which it's running, the hypervisor doesn't have to play as many virtualization tricks, and therefore the overall performance should be better than in a fully virtualized environment.
	www.fruug.org /Archive/2006-04/writeup.html (194 words)

	VMware releases free beta of virtualization software
		A slew of mostly Linux-based virtualization start-up companies, however, are challenging VMware's dominance.
		They say VMware's method is slower than their newer "paravirtualization" approach, which tweaks the processor instructions in guest operating system kernels so that they work better with resident hardware.
		Meanwhile VMware, through its full emulation, already supports Windows and other operating systems; XenSource, Virtual Iron and others have to rely on the new Intel or AMD chips with built-in VT to offer Windows.
	www.computerworld.com /printthis/2006/0,4814,108370,00.html (598 words)

	» Can virtualization double Apple's market share? \| George Ou \| ZDNet.com
		Of course, there are still many barriers to paravirtualization for the new Intel Mac.
		Intel would have to release new Core Duo CPUs that have VT support which is likely in the near future.
		All the borderline cases where people aren't sure about a Macintosh because of their requirements for Windows applications and games will all of sudden be more willing to accept the Mac.
	blogs.zdnet.com /Ou/?p=158 (873 words)

	VMware moves to deflect Xen, Microsoft - page 2 \| Tech News on ZDNet
		XenSource's Crosby said standardizing management interfaces through a standards group such as the Distributed Management Task Force, as Raghuram said VMware might, would be "terrific." On the other hand, XenSource CEO Moshe Bar said Xen's paravirtualization communication protocol is much more efficient than VMware's.
		As for the storage method, Xen simply uses standard Linux compression software, and Microsoft in April said it would license its own disk format, called Virtual Hard Disk, for free.
		Virtual Server is in the market now, but the company is pinning much of its hopes on a successor that takes the same paravirtualization approach as Xen.
	news.zdnet.com /2100-3513_22-5823141-2.html (746 words)

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