Re: nr_cpu_ids vs AMD 3970x(32 physical CPUs)

[peter enderborg]

On 7/3/20 5:57 PM, Uladzislau Rezki wrote:
> Hello, folk.
>
> I have a system based on AMD 3970x CPUs. It has 32 physical cores
> and 64 threads. It seems that "nr_cpu_ids" variable is not correctly
> set on latest 5.8-rc3 kernel. Please have a look below on dmesg output:
>
> <snip>
> urezki@pc638:~$ sudo dmesg | grep 128
> [    0.000000] IOAPIC[0]: apic_id 128, version 33, address 0xfec00000, GSI 0-23
> [    0.000000] smpboot: Allowing 128 CPUs, 64 hotplug CPUs
> [    0.000000] setup_percpu: NR_CPUS:512 nr_cpumask_bits:512 nr_cpu_ids:128 nr_node_ids:1

My 3950 do


[ÂÂÂ 0.005271] ACPI: SSDT 0x00000000CA1F5000 0003F1 (v02 ALASKA CPUSSDTÂ 01072009 AMIÂ 01072009)
[ÂÂÂ 0.108266] smpboot: Allowing 32 CPUs, 0 hotplug CPUs
[ÂÂÂ 0.111384] setup_percpu: NR_CPUS:8192 nr_cpumask_bits:32 nr_cpu_ids:32 nr_node_ids:1

(Fedora F32Â 5.6.18-300) What motherboard and BIOs do you use?


> ...
> [    0.000000] SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=128, Nodes=1
> [    0.000000] rcu:     RCU restricting CPUs from NR_CPUS=512 to nr_cpu_ids=128.
> [    0.000000] rcu: Adjusting geometry for rcu_fanout_leaf=16, nr_cpu_ids=128
> urezki@pc638:~$
> <snip>
>
> For example SLUB thinks that it deals with 128 CPUs in the system what is
> wrong if i do not miss something. Since nr_cpu_ids is broken(?), thus the
> "cpu_possible_mask" does not correspond to reality as well.
>
> Any thoughts?
>
> Thanks!
>
> --
> Vlad Rezki