Intel Platform QoS Technologies

Overview

Intel Platform QoS technologies are designed to help IT managers improve performance and manageability for virtual machines. The following list gives a brief overview, over available functionality and use-cases:

Feature	In	Description / Use-case
Cache Monitoring Technology (CMT)	Xen 4.5	CMT can be used to monitor Last Level Cache (LLC) usage by application threads. With this information, administrators and management applications can balance workloads more efficiently to improve both application performance and physical resource utilization. For example, CMT can be used to reduce the impact of the so-called "noisy neighbour" issue in multitenant cloud and data center environments. The noisy neighbour is the situation where you have two VMs (or more generally processes), VM A and B. VM A can be noisy in that it runs an algorithm that dirties many entries in the cache, evicting cache entries for VM B and thereby slowing down VM B. Cache Monitoring Technology (CMT) allows users to track which VMs are using how much cache and identify the noisy ones and take corrective action.
Cache Allocation Technology (CAT)	Xen 4.6	CAT allows system administrators to assign more L3 cache capacity to individual VMs, resulting in lower latency and higher performance for high-priority workloads such as NFV, real-time and video-on-demand applications.
Memory Bandwidth Monitoring (MBM)	Xen 4.6	MBM allows system administrators to identify memory bandwidth saturation on a Xen host that may be caused by several memory-intensive VMs running on the same host. Taking corrective actions, such as migrating VMs to a different Xen host, increases scalability and performance in the data center.

Man Pages and Reference

• XL Interrfaces
• XL Man Pages
• Architecture Software Development Manual (Vol 3b., Chapter 17.14 and 17.15, covers CMT, CAT, MBM, CDP)

Cache Monitoring Technology

For more information, see Benefit of Cache Monitoring and an Overview.

Cache Monitoring Information is exposed through XL via

$ xl psr-cmt-attach domid
$ xl psr-cmt-detach domid
$ xl psr-cmt-show cache_occupancy

A detailed description of the commands is available here

Also see

• Intel's Cache Monitoring Technology: Software Support and Tools
• Intel Cache Allocation Technology support
• Intel Cache Allocation Technology(CAT) design for XEN

Memory Bandwidth Monitoring

Memory Bandwidth Monitoring(MBM) is a new hardware feature available on Intel Broadwell and later server platforms which builds on the CMT infrastructure to allow monitoring of system memory bandwidth. It introduces two new monitoring event type to monitor system total/local memory bandwidth. The same RMID can be used to monitor both cache usage and memory bandwidth at the same time.

In Xen's implementation, MBM shares the same set of underlying monitoring service with CMT and can be used to monitor memory bandwidth on a per domain basis.

The xl interfaces are the same with that of CMT. The difference is the monitor type is corresponding memory monitoring type (local-mem-bandwidth/ total-mem-bandwidth instead of cache-occupancy). E.g. after a xl psr-cmt-attach:

$ xl psr-cmt-show local-mem-bandwidth domid
$ xl psr-cmt-show total-mem-bandwidth domid

Cache Allocation Technology

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