On Thu, May 30, 2019 at 08:56:03AM -0400, Andrew F. Davis wrote: > On 5/30/19 7:51 AM, Morten Rasmussen wrote: > > 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. > > > > I see the benefit of reporting the physical layout and packaging information > to user-space for tracking reasons, but from software perspective this > doesn't matter, and the resource partitioning should be described elsewhere > (NUMA nodes being the go to example). > > > 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). > > > > Seems my hypothetical case is already in the works :( > > > 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. > > > > Fair enough, it's a little late now to un-expose this info to userspace so > we should at least present it correctly. My worry was this getting out of > hand with layering, for instance what happens when we need to add die nodes > in-between cluster and socket? > We may have to, if there's a similar requirement on ARM64 as the one addressed by Len Brown's multi-die patch set. But for now, no one has asked for it. -- Regards, Sudeep
