Return number of numa nodes

[santagada]

Add a function like cpu_count but numa_count(), and on windows also a groups_count() could be very handy.

[Porges]

It would be nice to also have physical CPU count, since the code to do this on Windows is rather gnarly and requires dropping to ctypes.

[giampaolo]

It would be nice to also have physical CPU count

cpu_count(logical=False) is supposed to do it.

Back to the original request: is there an actual use case for NUMA nodes or it would just be for display (e.g. task manager apps)? Also, what do you mean by groups_count()?

[Porges]

@giampaolo that is physical core count, I’m meaning actual CPU/socket count.

[giampaolo]

Oh! Socket count. Mmm... That sounds sort of low levelish (would it really be useful?). Does Windows provide an API for this? I'm not sure we can support other platforms other than Windows.

Also (perhaps a personal consideration): the definition of what a CPU count really means is a bit confusing. The definition I ad-here to is this:
https://www.sqlskills.com/blogs/glenn/what-is-the-difference-between-physical-sockets-physical-cores-and-logical-cores/
...so 3 kinds:

1. socket count = number of sockets on the motherboard
2. physical count = number of physical CPU cores (can have more than 1 per socket)
3. logical count = physical count * number of hyper threading cores (hyper threading = INTEL's way to make 1 processor look like many processors)

psutil currently supports 2 and 3.

[santagada]

if you have more than 64 logical cpus, windows will put them on different groups, as an affinity mask is 64 bits (so you can only turn on and off 64 cpus). Knowing the group_count on windows is useful. More useful is the total logical cpus in all numa nodes, IIRC cpu_count() only return the number of logical cpu on the first numa node.

[giampaolo]

if you have more than 64 logical cpus, windows will put them on different groups, as an affinity mask is 64 bits (so you can only turn on and off 64 cpus).

Are you sure? On Windows cpu_logical() is implemented by using GetActiveProcessorCount(ALL_PROCESSOR_GROUPS). The name suggests all groups should be included.

psutil/psutil/arch/windows/cpu.c

Line 24 in 9e2ca97

ncpus = GetActiveProcessorCount(ALL_PROCESSOR_GROUPS);

As for NUMA: I'm no expert. Is it something which exists in Windows only?

[akrus]

One small note on NUMA nodes, it's not equal to socket count, e.g. 2x AMD EPYC 7601:

# numactl --hardware                                                                                                                                                     
available: 8 nodes (0-7)

And it depends on BIOS settings (Node Interleaving and a few more options for AMD CPUs).

In Linux you can get the info from sysfs:

# ls -1 /sys/devices/system/node/                                                                                                                                                                                         
has_cpu                                                                                                                                                                                                                                      
has_memory
has_normal_memory
node0
node1
node2
node3
node4
node5
node6
node7
online
possible
power
uevent

[giampaolo]

Closing as duplicate of #1392.