Saturday, 7 May 2011

KVM Slides from Red Hat Summit 2011

Update: Added link to Mark Wagner's KVM Performance Improvements and Optimizations slides that Andrew Cathrow posted on IRC.

This year at Red Hat Summit 2011 many presentations touched on KVM and virtualization. Slide decks are mostly online now so I took a look and highlighted those that I found most interesting. It's also worth checking again in a few days, hopefully the remaining slide decks will come online.

Converting, Inspecting, & Modifying Virtual Machines with Red Hat Enterprise Linux 6.1

Slides: libguestfs material, virt-v2v/virt-p2v material

Richard Jones (libguestfs) and Matthew Booth (virt-v2v/virt-p2v) cover the tools they have developed for manipulating virtual machines and their disk images. This looks really, really cool. KVM needs great tools for working with VM data rather than requiring the user to manually stack up disk partitioning, volume management, file system, and other functionality from scratch every time.

libguestfs has a small Linux-based appliance VM containing disk, volume, and file system tools. There are a bunch of command-line tools and a shell for interacting with appliance VM, which can access guest file systems without requiring root privileges on the host. Files can be downloaded/uploaded, partitions can be inspected, guest operating systems can be detected, and even the Windows registry can be edited using libguestfs.

KVM Performance Optimizations

Slides: KVM Performance Optimizations

Rik van Riel gave an overview of recent and future KVM performance optimizations:
  • vhost-net in-kernel virtio-net host accelerator.
  • kernel samepage merging (ksm) memory deduplication.
  • transparent hugepages automatic hugepages without administrator management.
  • pause look exiting as a solution to the lockholder preemption problem.
  • free page hinting and dynamic memory resizing to do intelligent swapping and waste fewer resources.

This is definitely worth reading if you're interested in virtualization internals. The presentation also answers the practical question of how ksm and transparent hugepages interact (both are memory management features that are not trivially compatible with each other). Asynchronous page faults weren't mentioned but I've linked to Gleb Natapov's KVM Forum 2010 slides on this feature since it fits in the same category.

System Resource Management Using Red Hat Enterprise Linux 6 cGroups

Slides: System Resource Management Using Red Hat Enterprise Linux 6 cGroups

Linda Wang and Bob Kozdemba explain the cgroups resource control features that have been added to Linux. Processes can be assigned to control groups which kernel subsystems like the scheduler or block layer take into account when arbitrating resources. Cgroups can be used to divide CPU, memory, block, and network resources. This looks much better than nice(1), ionice(1), and friends although cgroups are a complimentary feature and don't replace them. Next time a compile or a download is affecting interactive foreground processes I'll be sure to try out cgroups.

What does cgroups have to do with KVM? Since KVM is based on Linux and VMs are in fact userspace processes the cgroups features can be used to apply resource controls to VMs. Libvirt will play a role here and take care of setting up the right cgroups behind the scenes, but it is interesting to learn about the underlying mechanism and what it can do.

KVM Performance Improvements and Optimizations

Slides: KVM Performance Improvements and Optimizations

Mark Wagner gives an overview of performance tuning across CPU, memory (NUMA), disk, and network I/O. Lots of keywords and tweaks to dig into for anyone tuning KVM installations.

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