Avi Kivity summarized the kvm patches bound for the 2.6.25 kernel:

"Changes include performance and scalability improvements, completion of the portability work (though no new architectures are supported with this submission), support for new hardware features, using general userspace memory for kvm (which enables swapping guest memory as well as sharing memory among guests), as well as the usual cleanups and incremental fixes."

The Kernel-based Virtual Machine project, kvm, was started in mid-2006, and has been part of the Linux kernel since the 2.6.20 release in February of 2007. The recent changes can be browsed with gitweb.

"Incidentally i was thinking about using KVM for automated testing. Important pieces of hardware should get an in-KVM simulator/emulator, that way developers who do not own that hardware can do functionality testing too," Ingo Molnar suggested during a thread discussing a SCSI driver bug fix. Linus Torvalds was originally unimpressed by the idea:

"Using emulators to test device drivers is almost certain to be pointless. The problem with device drivers tends to be timing issues, odd hardware interactions, and lots of strange (and sometimes undocumented) behaviour and dependencies (eg things like 'you have to wait 50us after setting the reset bit until the hardware has actually reset'). These are all things that you'd generally not catch in emulation - because the emulation by necessity is only going to be a very weak picture of the real thing."

Alan Cox countered, "for some things. I do it a bit because you can use it to fake failures that are tricky to do in the real world. It won't tell you the driver works but its surprisingly good for testing for races (forcing IRQ delivery at specific points), buggy hardware you don't posses, and things like media failures and timeouts your real hardware refuses to do." Linus acquiesced conditionally, "I do agree that you likely find bugs, even if quite often it's exactly because the behaviour is something that will never happen on real hardware," then acknowledged previous debugging efforts by Alan, "but failure testing is very useful - I forget who it was who debugged some driver by taking a CD and just scratching it mercilessly to induce read errors ;)" Ingo added, "something like that wont enable 100% coverage (or even reasonable coverage for most hardware), so it's no replacement for actual hard testing, but it could push out the domain of minimally tested code quite a bit and increase the quality of the kernel."

Avi Kivitiy posted numerous KVM updates which Linus Torvalds merged into his mainline kernel source tree to be included in the upcoming 2.6.24 kernel. Avi summarized:

"Highlights include in-kernel pic/lapic/ioapic emulation, improved guest support, preemptibility, an improved x86 emulator, and a fair amount of cleanup.

"The changes outside drivers/kvm/ and include/linux/kvm*.h fix the CR8 mask definition (which is not otherwise used in the kernel) and expose some ioapic register definitions even if ioapic support is not compiled in. The diff is appended below."

"This report covers FreeBSD related projects between July and October 2007," began the latest FreeBSD Quarterly Status Report, posted by Brad Davis. He included a summary of the recent Google Summer of Code projects noting, "lots of participants are working getting their code merged back into FreeBSD." Regarding the upcoming FreeBSD 7.0 release he noted, "the bugs in the FreeBSD HEAD branch are being shaked out and it is being prepared for the FreeBSD 7 branching. If your are curious about what's new in FreeBSD 7.0 we suggest reading Ivan Voras' excellent summary."

Among the many projects discussed in the status report was work by Marko Zec on network stack virtualization, "the network stack virtualization project aims at extending the FreeBSD kernel to maintain multiple independent instances of networking state. This allows for networking independence between jail-like environmens, each maintaining its private network interface set, IPv4 and IPv6 network and port address space, routing tables, IPSec configuration, firewalls, and more." Another project discussed was the porting of Linux KVM, "a software package that can be used to create virtual machines fully emulating x86 hardware on top of machines supporting Intel VT-x or AMD-V virtualization extensions." The report noted, "Linux KVM has been ported to FreeBSD as a loadable kernel module, using the linux-kmod-compat port (in /usr/ports/devel/) to reuse as much as possible of the original source code, plus an userspace client consisting in a modified version of qemu, that uses KVM for the execution of its guests."

As expected, Linus Torvalds released the 2.6.23-rc1 kernel two weeks after the release of 2.6.22, ending the merge window, "and it has a *ton* of changes as usual for the merge window, way too much for me to be able to post even just the shortlog or diffstat on the mailing list". He noted, "I personally like how 'sendfile' is now totally gone internally, and the kernel now ends up doing all that with splice insted. Good riddance, although we'll obvously end up supporting the old user level interfaces for a long time." Linus went on to summarize the other changes:

"Lots of architecture updates (for just about all of them - x86[-64], arm, alpha, mips, ia64, powerpc, s390, sh, sparc, um..), lots of driver updates (again, all over - usb, net, dvb, ide, sata, scsi, isdn, infiniband, firewire, i2c, you name it).

"Filesystems, VM, networking, ACPI, it's all there. And virtualization all over the place (kvm, lguest, Xen).

"Notable new things might be the merge of the cfs scheduler, and the UIO driver infrastructure might interest some people."

Rusty Russell's lguest was recently merged into the upcoming 2.6.23 Linux kernel. The merge comment describes the project, "lguest is a simple hypervisor for Linux on Linux. Unlike kvm it doesn't need VT/SVM hardware. Unlike Xen it's simply 'modprobe and go'. Unlike both, it's 5000 lines and self-contained." The comment goes on to note:

"Performance is ok, but not great (-30% on kernel compile). But given its hackability, I expect this to improve, along with the paravirt_ops code which it supplies a complete example for. There's also a 64-bit version being worked on and other craziness.

"But most of all, lguest is awesome fun! Too much of the kernel is a big ball of hair. lguest is simple enough to dive into and hack, plus has some warts which scream 'fork me!'."

A recently merged KVM patchset included support for guest SMP, various performance improvements, and suspend/resume fixes. KVM stands for Kernel-based Virtual Machine, "a full virtualization solution for Linux on x86 hardware containing virtualization extensions". In regards to the recently merged guest SMP support which will be part of the upcoming 2.6.23 kernel, Avi Kivity noted:

"Guest smp is fully operational. Kernel build on 2-way smp is 40% faster than on a up guest. Expect significant performance improvements from in-kernel apic and from further tuning."

Andrew Morton [interview] sent out the latest lguest patches for review, noting that he intends to merge the code into the mainline kernel, "some concern was expressed over the lguest review status, so I shall send the patches out again for people to review, to test, to make observations about the author's personal appearance, etc. I'll plan on sending these patches off to Linus in a week's time, assuming all goes well." The project's FAQ notes, "lguest is designed to be simple to use and modify, with the aim of keeping the codebase small. Currently it's around 5000 lines including userspace utility, whereas kvm is over 10 times that size, and Xen is around 10 times bigger again (of course, both have far more features)."

The lguest patches are written and maintained by Rusty Russell [interview] who also authored Rusty's Remarkably Unreliable Guide to Lguest, the project's documentation. The guide explains, "lguest is designed to be a minimal hypervisor for the Linux kernel, for Linux developers and users to experiment with virtualization with the minimum of complexity. Nonetheless, it should have sufficient features to make it useful for specific tasks, and, of course, you are encouraged to fork and enhance it." In the FAQ, lguest is compared to kvm [story], "kvm requires hardware virtualization support (most recent Intel and AMD chips have it), but it can run almost any Operating System (since it does full virtualization. It also has 64-bit support. Lguest doesn't do full virtualization: it only runs a Linux kernel with lguest support." The FAQ also compares lguest to Xen, "Xen is similar, in that it doesn't need hardware virtualization support (although it can use it), but Xen supports an extensive range of features such as PAE (ie. lots of memory), SMP guests, 64-bit. You have to boot your kernel under the Xen hypervisor; you can't simply modprobe when you want to create a guest."

Avi Kivity [interview] announced significant performance improvements and support for running 32-bit Windows Vista as a guest within the latest release of KVM. Originally merged into the 2.6.20 mainline Linux kernel [story], KVM stands for Kernel-based Virtual Machine, "a full virtualization solution for Linux on x86 hardware containing virtualization extensions". Regarding the new release, Avi announced:

"The happy theme of today's kvm is the significant performance improvements, brought to you by a growing team of developers. I've clocked kbuild at within 25% of native. This release also introduces support for 32-bit Windows Vista."

Avi Kivity is the lead developer and maintainer of the Kernel-based Virtual Machine project, better known as kvm. The project was started in mid-2006, and has been part of the Linux kernel since the 2.6.20 release in February of 2007. kvm is a full virtualization system for x86-based Linux hosts, allowing users to run isolated x86 guest operating systems in virtual machines.

Linux creator Linus Torvalds announced the release of the 2.6.20 kernel, summarizing, "a lot of stuff. All over. And KVM." He further noted, "I tried rather hard to make 2.6.20 largely a 'stabilization release'. Unlike a lot of kernels lately, there aren't really any big fundamental changes to some core infrastructure area, and while we always have bugs, I really am hoping that we fixed many more than we introduced." His announcement started with a news parody, "in a widely anticipated move, Linux 'headcase' Torvalds today announced the immediate availability of the most advanced Linux kernel to date, version 2.6.20." Linus continued:

"As ICD head analyst Walter Dickweed put it: "Releasing a new kernel on Superbowl Sunday means that the important 'pasty white nerd' constituency finally has something to do while the rest of the country sits comatose in front of their 65" plasma screens."

"Walter was immediately attacked for his racist and insensitive remarks by Geeks without Borders representative Marilyn vos Savant, who pointed out that not all of their members are either pasty nor white. "Some of them even shower!" she added, claiming that the constant stereotyping hurts nerds' standing in society.

Geeks outside the US were just confused about the whole issue, and were heard wondering what the big hoopla was all about. Some of the more culturally aware of them were heard snickering about balls that weren't even round.

Avi Kivity suggested that combining KVM, the Kernel-based Virtual Machine [story], with the dyntick patch [story] could improve overall KVM performance. He noted that it would likely improve performance of both the host by "avoiding expensive vmexits due to useless timer interrupts," as well as on the guest by "reducing the load on the host when the guest is idling (currently an idle guest consumes a few percent cpu)". Ingo Molnar [interview] pointed out that KVM with his -rt kernel already works with dynticks enabled on both the host and the guest, "using the dynticks code from the -rt kernel makes the overhead of an idle guest go down by a factor of 10-15". Ingo added that he hopes the dyntick patch will be ready to be merged into the upcoming mainline 2.6.21 kernel.

Rik van Riel [interview] noted that there were other ways to reduce the load of the guest when it's idling, "you do not need dynticks for this actually. Simple no-tick-on-idle like Xen has works well enough." Ingo explained, "s390 (and more recently Xen too) uses a next_timer_interrupt() based method to stop the guest tick - which works in terms of reducing guest load, but it doesnt stop the host-side interrupt. The highest quality approach is to have dynticks on both the host and the guest, and this also gives high-resolution timers and a modernized time/timer-events subsystem for both the host and the guest."