The new host kernel networking backend, vhost, is a fully supported feature in Red Hat Enterprise Linux 6.1. vhost provides superior throughput and latency over the userspace implementation.
The qcow2 image format now supports caching of metadata. Additionally, support is added for live snapshots using external qcow2 images.
ioeventfd is now available, providing faster notification of block I/O.
The KVM hypervisor in Red Hat Enterprise Linux 6 features Kernel SamePage Merging (KSM), allowing KVM guests to share identical memory pages. Page sharing reduces memory duplication, allowing a host with similar guest operating systems to run more efficiently.
KSM in Red Hat Enterprise Linux 6.1 is Transparent HugePage aware. KSM has the ability to scan subpages inside hugepages and split them when merging is possible.
Additionally, KSM enablement can now be controlled on a per-VM basis.
PCI configuration space access is improved, enabling a broader set of PCI devices to be device-assigned to guest VMs.
In Red Hat Enterprise Linux 6.1, the Time Stamp Counter (TSC) synchronization can now be automatically detected on guest bootup or when a host CPU is hot-plugged. Additionally, the TSC synchronization frequency is adjusted after a live migration.
Additionally, the new drive_del command allows libvirt to safely remove a block device from a guest.
