Bug 877615

Summary:	sys-kernel/gentoo-kernel-5.19.16: /sys/devices/system/cpu/possible lists non-existing processors (or nproc/glibc uses it wrong)
Product:	Gentoo Linux	Reporter:	Michał Górny <mgorny>
Component:	Current packages	Assignee:	Distribution Kernel Project <dist-kernel>
Status:	CONFIRMED ---
Severity:	normal	CC:	base-system
Priority:	Normal
Version:	unspecified
Hardware:	All
OS:	Linux
Whiteboard:
Package list:		Runtime testing required:	---

Description Michał Górny archtester

2022-10-19 03:46:02 UTC

$ uname -r
5.19.16-gentoo-dist
$ cat /sys/devices/system/cpu/possible 
0-31
$ cat /sys/devices/system/cpu/present 
0-11
$ cat /sys/devices/system/cpu/online 
0-11
$ cat /sys/devices/system/cpu/offline 
12-31


This seems to cause `nproc --all` to think I have 32 logical CPUs installed, even though 12 is the correct number.  I haven't verified it here but according to others, "offline" is empty on their systems with <=5.15 kernels.

Comment 1 Greg Kubaryk 2022-10-19 04:04:13 UTC

It was requested that I provide this data point here that offline may not be relevant as originally thought. (Yes, I know the box needs a reboot.)

$ uname -r
5.19.14
$ nproc
8
$ nproc --all
8
$ cat /sys/devices/system/cpu/possible 
0-7
$ cat /sys/devices/system/cpu/present
0-7
$ cat /sys/devices/system/cpu/online
0-7
$ cat /sys/devices/system/cpu/offline 
,8-15

Comment 2 Michał Górny archtester

2022-10-19 04:05:57 UTC

Ok, the problem seems to be actually in "possible" as that is what nproc seems to read through glibc.

Comment 3 Sam James archtester

2023-08-24 20:30:39 UTC

Was this in a container? juippis and I discussed a problem like this before in Docker in the context of Portage trying to figure out the # of active CPUs for load average.