Here is a brief overview of the new Intel® VT technologies:
Cache Monitoring Technology (CMT) - allows flexible real time monitoring of the last level cache (LLC) occupancy on per core, per thread, per application or per VM basis. Read the raw value from the IA32_QM_CTR register, multiply by a factor given in the CPUID field CPUID.0xF.1:EBX to convert to bytes, and voila! This monitoring can be quite useful in detecting the cache hungry “noisy neighbors,” characterizing the quiet threads, profiling the workloads in multi-tenancy environments, advancing cache-aware scheduling and/or all of the above. Based on the CMT readings, schedulers can take subsequent intelligent actions to move and balance the loads to meet any service level agreement (SLA) in a policy driven manner. Intel® 64 and IA-32 Architectures Software Developer’s Manual (SDM) volume-3 chapter-17.14 provides the CMT programming details. CMT reference code is also available for evaluation under BSD license. For commercial use, please use the CMT cgroup and perf monitoring code being upstreamed for Linux, and both KVM and Xen.
VMCS Shadowing - accelerates nested virtualization - basically a hypervisor in a hypervisor. The root HV privileges are extended to the guest HV. Thanks to the acceleration that the shadow VMCS provides, a guest software can run with minimal performance impact and without needing any modification. But why would you do that? Because this technology enables you to consolidate heterogeneous application VMs, containers, and workloads within a single super host VM. You could reduce your cost of using the cloud by extracting more benefit from a single licensed host VM – “virtualization of the cloud” if you will. Your cloud service providers (CSP) could make you feel more empowered in controlling your HV and software choices without intervention from the CSP. Other practical use cases include creating web based labs, software development and test environments, trainings, make shift arrangements during migration, disaster recovery, rapid prototyping, and reduction of security attack surfaces, etc. VMCS Shadowing code is upstreamed in KVM-3.1 and Xen-4.3 onwards. More than 58% reduction in kernel build time, >50% reduction in cpu signaling, and >125% increase in IO throughput have been reported on Haswell with VMCS Shadowing applied to nested virtualization test cases. Please refer to Intel (SDM) volume-3 chapter-24 for VMCS Shadowing programming details.
Extended Page Table Accessed and Dirty bits (EPT A/D bits) – This technology improves performance during memory migration and creates interesting opportunities for virtualized fault tolerance usages. You probably already understand that guest OS expects contiguous physical memory, and the host VMM must preserve this illusion. EPT maps guest physical address to host address that allows guest OS to modify its own page tables freely, minimizes VM exits and saves memory. The new addition of (A)ccessed and (D)irty flag bits in EPT further optimizes the VM Exits during live migration, especially when high-freq resetting of permission bits is required. Up to date memory is pre-migrated leaving only the most recently modified pages to be migrated at the final migration stage. In turn, this minimizes the migration overhead and the migrated VM downtime. EPT(A) bits code has been upstreamed in KVM-3.6 and Xen-4.3; and EPT(D) bits code up-streaming is in the works. Programing details for EPT A/D bits can be found in Intel SDM volume-3, chapter-28.
Data Direct IO Enhancements - improve application bandwidth, throughput and CPU utilization. Now in addition to targeting the LLC for IO traffic, you can also control the LLC way assignment to specific cores. On Haswell, a direct memory access (DMA) transaction can end up in 8 ways of the LLC without hitting the memory first. Because both the memory and in-cache utilization due to networking IO is reduced, the IO transaction rate per socket improves, latency shrinks and power is saved. Cloud and data center customers can profusely benefit from the increased IO virtualization throughput performance. Storage targets and appliances can practically eliminate the need of full offload solutions. Data Plane application and appliance makers can improve and optimize transaction rates, especially for small packets and UDP transactions. DDIO use cases galore. For a detailed discussion about your specific application, please do contact your local Intel representative.
Happy virtualizing with the latest Intel® Xeon® E5-2600 v3 Product Family! At Intel, we’ll be eagerly waiting to hear about all those cool innovations and new businesses that you’ll be building around these newly introduced virtualization technologies. Comments are very welcome!
