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4.5.2. Virtualization Optimizations

Because KVM utilizes kernel functionality, KVM-based virtualized guests immediately benefit from all bare-metal optimizations. Red Hat Enterprise Linux also includes a number of enhancements to allow virtualized guests to approach the performance level of a bare-metal system. These enhancements focus on the I/O path in storage and network access, allowing even intensive workloads such as database and file-serving to make use of virtualized deployment. NUMA-specific enhancements that improve the performance of virtualized systems include:
CPU pinning
Virtual guests can be bound to run on a specific socket in order to optimize local cache use and remove the need for expensive inter-socket communications and remote memory access.
transparent hugepages (THP)
With THP enabled, the system automatically performs NUMA-aware memory allocation requests for large contiguous amounts of memory, reducing both lock contention and the number of translation lookaside buffer (TLB) memory management operations required and yielding a performance increase of up to 20% in virtual guests.
kernel-based I/O implementation
The virtual guest I/O subsystem is now implemented in the kernel, greatly reducing the expense of inter-node communication and memory access by avoiding a significant amount of context switching, and synchronization and communication overhead.