Bug 81445 - SMP kernel fails to see second physical CPU with hyperthreading disabled.
SMP kernel fails to see second physical CPU with hyperthreading disabled.
Product: Red Hat Linux
Classification: Retired
Component: kernel (Show other bugs)
All Linux
medium Severity medium
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Assigned To: Arjan van de Ven
Brian Brock
Depends On:
Blocks: 79579
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Reported: 2003-01-09 11:16 EST by Larry Troan
Modified: 2016-04-18 05:38 EDT (History)
2 users (show)

See Also:
Fixed In Version:
Doc Type: Bug Fix
Doc Text:
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Clone Of:
Last Closed: 2003-04-05 11:31:52 EST
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oVirt Team: ---
RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: ---

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Description Larry Troan 2003-01-09 11:16:57 EST
SMP kernel fails to see second physical CPU with hyperthreading disabled 

Operating System: Red Hat 8.1 Beta 1

Server (and Generation): ML370-G3
Rom version: P28 (8/16/2002)  
Processor info (class, speed & number of processors): 2 - 2.2GHz/512KB Xeons
Memory (amount only): 512M
What cards are installed and slot locations (also include firmware versions):  
  Base configuration
  Broadcom NetXtreme boot rom v2.2.7

Drive locations: Internal bays 0 and 1 (9.1GB each)

Boot controller:  3.02.01 Compaq Ultra 3 (Adaptec)

Steps to reproduce:
1) Disable hyperthreading in RBSU
2) Install the OS (text-mode)
3) After installation, prompted to load either SMP or UP kernel by grub, choose SMP.
4) cat /proc/cpuinfo, reports only one CPU instead of 2.
5) init 6, enabled hyperthreading in RBSU and repeat step 3.
6) cat /proc/cpuinfo, reports four (4) CPUs now.

uname -a output: Linux ml370g3 2.4.19-0.pp.15smp #1 SMP Thu Nov 14 13:57:02 EST
2002                  i686 i686 i386 GNU/Linux

Is the issue reproducible? Yes, repeatable on this system, as well as the 380-G3.  

Workaround: None found.
Action by: Bryan.Leopard
Issue Registered
Action by: arjanv
please try "acpi=off noht" as kernel option.
If that fixes it your ACPI bios has a bug where it enumerates CPU's wrong.

Status set to: Waiting on Client

Action by: Bryan.Leopard
That does work, in the sense that it allows the system to see
both physical processors, but HT is obviously still an issue.  

Status set to: Waiting on Tech
Comment 1 Larry Troan 2003-01-09 11:17:58 EST
Issue Tracker 11856
Comment 2 Arjan van de Ven 2003-01-10 04:41:34 EST
please retry this with the rawhide kernel; the HT cpu enumeration is
significantly modified there.
Comment 3 Arjan van de Ven 2003-04-05 11:31:52 EST
closed due to inactivity in NEEDINFO

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