Bug 66387

Summary:	SMP kernel for dual Xeon "see" four processors
Product:	[Retired] Red Hat Linux	Reporter:	Benoit <ppbenoit>
Component:	kernel	Assignee:	Arjan van de Ven <arjanv>
Status:	CLOSED NOTABUG	QA Contact:	Brian Brock <bbrock>
Severity:	medium	Docs Contact:
Priority:	medium
Version:	7.3
Target Milestone:	---
Target Release:	---
Hardware:	i586
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	Bug Fix
Doc Text:		Story Points:	---
Clone Of:		Environment:
Last Closed:	2003-06-07 19:11:24 UTC	Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description Benoit 2002-06-09 16:57:08 UTC

From Bugzilla Helper:
User-Agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1)

Description of problem:
I have installed RH 7.3 on Tyan i860 dual Xeon motherboard without any 
problems.
I can run to instances of the same program at the same time (very long batch 
program for neural network computation):
1) they both run at the same speed as they individually run one a single 
processor motherboard
2) xosview shows the two processors working at 100%
3) lm_sensors show one processor at 42 degrees Celsius and the other at 49 
degrees (box is 37 degrees inside)
Up to that point everything is ok.
Then I have updated the kernel from from 2.4.18-3 to 2.4.18-4 with red hat 
network because of the bug fix "kernel panic on smp system".

Boot with new 2.4.18-4smp kernel:
1) xosview doesn't work anymore, even when reinstalled. 
2) running to instances of the same program mentioned above at the same time 
provide a loss of performance of 50% in both programs sugesting that one 
processeur is not working
3) lm_sensors indicate that one processor is 37 degree (the other still 49) 
suggesting too that one processor is not working.

Reboot with 2.4.18-3smp old kernel:
1) xosview is working, but indicates that there is FOUR processors !
2) programs perfomances still bad
3) lm_sensors still show one processor at 37 degree

xosview indicates that processors 2 and 3 are working 100% (processors 0 and 1 
from 0 to 3%), but from time to time (not very ofen),without any action of my 
own, xosview indicates that processor 0 and 3 are working ` 100%; and at that 
point performances of the programmes turn back good, lm_sensors indicates that 
both processors are hot (42 and 49 degrees), and then things went back bad as 
before without any notice or action.

More funny, I can run third instance of my program and xosview said there is 
three processors working at 100%...


Version-Release number of selected component (if applicable):


How reproducible:
Didn't try

Steps to Reproduce:
1. I don't want reinstall RH7.3 and upgrade again the kernel.
2.
3.
	

Additional info:

Comment 1 Arjan van de Ven 2002-06-10 09:03:28 UTC

Something went wrong in -4 that broke xosview. The actual work should be fine
though, it's just the measurement program that gives the wrong data; top should
also still provide the right info.

Comment 2 Benoit 2002-06-10 18:14:25 UTC

no, top doesn't still produce the right info.

Comment 3 Benoit 2002-06-11 17:14:50 UTC

I have found where the problem come from : the bios has Hyper-Thread enable !
I have just disbled it and everything ok.
There is still one question now, why and how when there is already a process 
running on a physical processor the kernel choose to run a second process to 
the second logical processor attache to same physical processor the first 
process is already running on ?
Is it a option or a command to force a task to run on a specific physical 
processor ?
P.S. I found the answer of my problem in the support database of suse linux.

Comment 4 paulm 2002-10-04 19:33:56 UTC

I am seeing double processors on xeon servers also. My kernel is 2.4.18-10
Does redhat consider this a bug?

Comment 5 Arjan van de Ven 2002-10-04 19:35:55 UTC

no
you see 4 virtual processors...
you paid money to intel for the hyperthreading feature... use it! :)