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Fewer than expected CPUs are online

Posted: January 7th, 2019, 6:53 am
by eugene
Hi folks,

I'm running ipfire on an Intel Xeon Silver 4114. The server CPU specs are:
- 2 sockets
- 10 core/CPU
- 2 threads/core

dmidecode shows the correct CPU count but lscpu shows that only 32 are online. Printing "processor" from /proc/cpuinfo further confirms the fact.

Code: Select all

$ dmidecode -t processor | grep "Thread Count"
	Thread Count: 20
	Thread Count: 20

$ lscpu | grep "^CPU(s).*"
CPU(s):                32

$ cat /proc/cpuinfo |grep processor
processor	: 0
processor	: 1
processor	: 2
processor	: 3
processor	: 4
processor	: 5
processor	: 6
processor	: 7
processor	: 8
processor	: 9
processor	: 10
processor	: 11
processor	: 12
processor	: 13
processor	: 14
processor	: 15
processor	: 16
processor	: 17
processor	: 18
processor	: 19
processor	: 20
processor	: 21
processor	: 22
processor	: 23
processor	: 24
processor	: 25
processor	: 26
processor	: 27
processor	: 28
processor	: 29
processor	: 30
processor	: 31
This is the first time I've observed this discrepancy. Any ideas?

Thanks in advance!

Re: Fewer than expected CPUs are online

Posted: January 7th, 2019, 7:50 am
by eugene
The max CPU count is pegged to 32 in the code. Anyone knows why this is so?

Code: Select all

$ grep NR_CPUS /boot/config-`uname -r`
CONFIG_NR_CPUS=32

Re: Fewer than expected CPUs are online

Posted: January 7th, 2019, 11:39 am
by Deepcuts
The reason might be to keep the kernel size as low as possible.
I recall any extra CPU would increase the kernel by 8K.
In the past, many distros had even more drastic limitations, like 8-10 CPUs.

Re: Fewer than expected CPUs are online

Posted: January 7th, 2019, 1:38 pm
by eugene
That's interesting. Is it necessary with today's hardware?

Re: Fewer than expected CPUs are online

Posted: January 7th, 2019, 1:43 pm
by MichaelTremer
Hello,

indeed nobody has used a system with that man processor cores. You can file a ticket and I can assign that to Arne to increase this number in the next kernel release.

-Michael

Re: Fewer than expected CPUs are online

Posted: January 7th, 2019, 1:55 pm
by eugene
Sure, but it so happens that my server has that many cores :D

Where should I file the ticket?

Re: Fewer than expected CPUs are online

Posted: January 7th, 2019, 2:02 pm
by MichaelTremer

Re: Fewer than expected CPUs are online

Posted: January 8th, 2019, 2:37 am
by eugene
Submitted it here https://bugzilla.ipfire.org/show_bug.cgi?id=11963.

Thanks heaps!

Re: Fewer than expected CPUs are online

Posted: January 8th, 2019, 11:56 am
by MichaelTremer
eugene wrote:
January 8th, 2019, 2:37 am
Submitted it here https://bugzilla.ipfire.org/show_bug.cgi?id=11963.

Thanks heaps!
Thank you. A new kernel will be released with Core Update 128 which will include this change...