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I just upgraded my bi-Xeon server with 20 cores/proc (i.e. a 40 cores server) from 18.04 to 20.04 and now the system is only viewing 1 processor!

The BIOS is correctly seeing the whole system (2 procs, 20 cores each)

The boot options are

Kernel command line: BOOT_IMAGE=/boot/vmlinuz-5.4.0-84-generic root=UUID=051241f1-7c3d-472a-b519-003008a805d4 ro mem_sleep_default=deep quiet splash acpi=off vt.handoff=7

Scrolling through dmesg output I find the following lines:

[    3.164688] smp: Bringing up secondary CPUs ...
[    3.164689] smp: Brought up 1 node, 1 CPU
[    3.164690] smpboot: Max logical packages: 1
[    3.164691] smpboot: Total of 1 processors activated (4200.00 BogoMIPS)

Please help...

ubfan1
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efji
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  • Try booting without the acpi=off, that can disable all the other cores. Check that your firmware is up to date if you cannot boot without the acpi=off. – ubfan1 Sep 08 '21 at 16:30
  • Thanks a lot ubfan1, it worked! I have now all my procs, but the reason why I had put this "acpi=off" in the boot options is back: as you imagine it is a server and not a laptop and I don't want it to go in sleep mode as soon as it is unbusy. Do you have any hint to disable permanently the sleep mode ? – efji Sep 09 '21 at 09:20
  • There are lots of acpi_? options, see https://help.ubuntu.com/community/BootOptions Maybe try acpi=ht I added the server tag to maybe get responses from someone who's done this before. – ubfan1 Sep 09 '21 at 15:24
  • I found this https://askubuntu.com/questions/1354040/ubuntu-20-04-server-suspends-or-goes-to-sleep-after-a-certain-period-of-time-ca?rq=1 and in my case changing the options in /etc/gdm3/greeter.dconf-defaults solved the problem. Thanks. – efji Sep 09 '21 at 16:19
  • You can answer your own question and in a few days accept it, gaining a few points in the process and helping others. – ubfan1 Sep 09 '21 at 16:55

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As ubfan1 suggested, the boot option "acpi=off" was the reason of the non-detection of the multiple processors. Without it, they are back! But the reason why I had added it was the control of the sleep mode: I wanted to avoid the server to enter in sleep mode after a few minutes of inactivity. It has been finaly achieved, without the "acpi=off" boot option, by modifying /etc/gdm3/greeter.dconf-defaults as suggested in the thread Ubuntu 20.04 server suspends or goes to sleep after a certain period of time, causing ssh to time out

efji
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