Hi Daniel, Daniel P. Berrangé, Mar 12, 2024 at 16:49:
> The point still stands though. NUMA node ID numbers are not > guaranteed to be the same as socket ID numbers. Very often > then will be the same (which makes it annoying to test as it > is easy to not realize the difference), but we can't rely on > that. > > > I'm using functions of libnuma to populate the maxpkgs of the host. > > I tested this on different Intel CPU with multiple packages and this > > has always returned the good number of packages. A false positive ? > > maxpkgs comes from vmsr_get_max_physical_package() which you're > reading from sysfs, rather than libnuma. > > > So here I'm checking if the thread has run on the package number 'i'. > > I populate 'numa_node_id' with numa_node_of_cpu(). > > > > I did not wanted to reinvent the wheel and the only lib that was talking > > about "node" was libnuma. > > I'm not actually convinced we need to use libnuma at all. IIUC, you're > just trying to track all CPUs within the same physical socket (package). > I don't think we need to care about NUMA nodes to do that tracking. > Alright, having a deeper look I'm actually using NUMA for 2 info: - How many cpu per Package: this helps me calculate the ratio. - To whom package the cpu belongs: to calculate the ratio with the right package energy counter. Without libnuma, I'm bit confused on how to handle this. Should I parse /sys/bus/node/devices/node* to know how many packages ? Should I parse /sys/bus/node/devices/node0/cpu0/topology/core_cpus_list to handle which cpu belongs to which package ? Would that be too cumbusome for the user to enter the detail about how many packages and how many cpu per pakages ? i.e: -kvm,rapl=true,maxpkgs=2,cpupkgs=8,rapl-helper-socket=/path/sock.sock > > Maybe I'm wrong assuming that a "node" (defined as an area where all > > memory has the same speed as seen from a particular CPU) could lead me > > to the packages number ? > > Historically you could have multiple sockets in the same NUMA node > ie a m:1 mapping. > > These days with AMD sockets, you can have 1 socket compromising > many NUMA nodes, as individual dies within a socket are each their > own NUMA node. So a 1:m mapping > > On Intel I think it is still typical to have 1 socket per numa > node, but again I don't think we can rely on that 1:1 mapping. > > Fortunately I don't think it matters, since it looks like you > don't really need to track NUMA nodes, only sockets (phnysical > package IDs) > Very informative, thanks ! > With regards, > Daniel > -- > |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| > |: https://libvirt.org -o- https://fstop138.berrange.com :| > |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :| Regards, Anthony
