Re: [libvirt] RFC: add Intel CMT feature support

-----Original Message----- From: Peter Krempa [mailto:pkrempa@redhat.com] Sent: Monday, June 29, 2015 5:44 PM To: Ren, Qiaowei Cc: libvir-list(a)redhat.com Subject: Re: [libvirt] RFC: add Intel CMT feature support On Sat, Jun 27, 2015 at 03:45:21 +0000, Ren, Qiaowei wrote: > Hi All, > > Some Intel processor families (e.g. the Intel Xeon processor E5 v3 family) introduced some PQos (Platform Qos) features to monitor or control shared resource. > > - CMT (Cache Monitoring Technology): measure the usage of cache by applications running on the platform. > - CAT (Cache Allocation Technology): enable an OS or Hypervisor/VMM to specify the amount of cache space into which an application can fill. > - MBM (Memory Bandwidth Monitoring): build on the CMT infrastructure to allow monitoring of bandwidth from one level of the cache hierarchy to the next - in this case focusing on the L3 cache, which is typically backed directly by system memory. As a result of this implementation, memory bandwidth can be monitored. > > For more information, see "Intel 64 and IA-32 Architectures Software Developer's Manual". > > Among these PQos features, currently CMT patches has been merged into Linux kernel mainline. So this patch series proposed in this mail will focus on CMT feature support in libvirt. > > At the library API layer, I plan on adding cache related field into virDomainInfo and virNodeInfo: > > Add "cache" member into virNodeInfo to get total size of cache in one node. > struct virNodeInfo { > ... > unsigned int cores; /* number of cores per socket, total number of > processors in case of unusual NUMA topology*/ > unsigned int threads; /* number of threads per core, 1 in case of > unusual numa topology */ > + unsigned int cache; /* cache size in bytes */ We don't allow changing/adding members to public structures. You probably will be better of by adding this info to the capabilities XML.

> }; > > Add "cacheOcc" member into virDomainInfo to get cache occupancy for one VM. > struct virDomainInfo { > ... > unsigned short nrVirtCpu; /* the number of virtual CPUs for the domain */ > unsigned long long cpuTime; /* the CPU time used in nanoseconds */ > + unsigned long long cacheOcc; /* the cache occupancy in Bytes */ Neither this structure can be modified. > }; > > With this change, those applications like OpenStack based on libvirt can collect cache usage for metering and monitoring (e.g. any VM using more than X% of cache). You can use the bulk stats API (virDomainListGetStats) to add this field since that uses the typed parameter approach which can be extended.

> > Because CMT implementation in Linux kernel is based on perf mechanism and there is no nice and public API library for perf, I have to wrapper system call for perf in libvirt to use CMT feature, and enable/disable perf event for CMT when VM is created/destroyed. > > Any thoughts on this plan before I start submitting code patches? Do you think whether I need add several new APIs and XML element for CMT feature (or more PQos features)? >