On Wed, May 29, 2019 at 07:39:17PM -0400, Andrew F. Davis wrote: > On 5/29/19 5:13 PM, Atish Patra wrote: > >From: Sudeep Holla <sudeep.holla@xxxxxxx> > > > >The current ARM DT topology description provides the operating system > >with a topological view of the system that is based on leaf nodes > >representing either cores or threads (in an SMT system) and a > >hierarchical set of cluster nodes that creates a hierarchical topology > >view of how those cores and threads are grouped. > > > >However this hierarchical representation of clusters does not allow to > >describe what topology level actually represents the physical package or > >the socket boundary, which is a key piece of information to be used by > >an operating system to optimize resource allocation and scheduling. > > > > Are physical package descriptions really needed? What does "socket" imply > that a higher layer "cluster" node grouping does not? It doesn't imply a > different NUMA distance and the definition of "socket" is already not well > defined, is a dual chiplet processor not just a fancy dual "socket" or are > dual "sockets" on a server board "slotket" card, will we need new names for > those too.. Socket (or package) just implies what you suggest, a grouping of CPUs based on the physical socket (or package). Some resources might be associated with packages and more importantly socket information is exposed to user-space. At the moment clusters are being exposed to user-space as sockets which is less than ideal for some topologies. At the moment user-space is only told about hw threads, cores, and sockets. In the very near future it is going to be told about dies too (look for Len Brown's multi-die patch set). I don't see how we can provide correct information to user-space based on the current information in DT. I'm not convinced it was a good idea to expose this information to user-space to begin with but that is another discussion. Morten
