On 24/9/21 5:38 pm, Michael wrote: > On Friday, 24 September 2021 10:06:49 BST Peter Humphrey wrote: >> On Thursday, 23 September 2021 19:20:52 BST Michael wrote: >>> Out of interest, have you tried booting a NUMA enabled kernel to see what >>> dmesg reports? >> Yes, it's been enabled ever since I had a dual-socket motherboard, years >> ago. I didn't understand why I did or didn't need it until I read Miles's >> post yesterday (thanks, Miles). I don't know why it hadn't been made clear >> in any websites I've visited. >> >>> On an old laptop, which definitely has only a single AMD >>> APU, I get: >>> >>> $ dmesg | grep -i NUMA -A2 >>> [ 0.002078] No NUMA configuration found >>> [ 0.002080] Faking a node at [mem >> 0x0000000000000000-0x000000042effffff] >> >>> [ 0.002085] NODE_DATA(0) allocated [mem 0x42effc000-0x42effffff] >> I had something similar. Oddly, with NUMA configured I get "not found" and >> without it I get "pci_bus 0000:00: on NUMA node 0". The system seems to run >> happily either way. > Sorry I should have made it clear - the above "No NUMA configuration found" > message was obtained *with* NUMA enabled in my kernel. > > I suppose "NUMA on node 0" is the default first socket, which the kernel sets > up. If the kernel can't find a second CPU it will be 'faking' a multi-CPU > memory allocation setup, when it comes to allocate memory to the only CPU > available. If the kernel does not have NUMA enabled then it doesn't need to > fake anything. It will treat the hardware as a single socket MoBo and no > further tests would be undertaken. All suppositions of course, I haven't > looked at the code. ;-)
Try "numactl --hardware" (from the numactl package) rattus ~ # numactl --hardware available: 1 nodes (0) node 0 cpus: 0 1 2 3 4 5 6 7 8 9 10 11 node 0 size: 31942 MB node 0 free: 7210 MB node distances: node 0 0: 10 rattus ~ # (Intel 6 core - NUMA emulation in the kernel.) I can only find testing NUMA code and hardware as a reason to have emulation enabled on a non-NUMA system? BillK
