Red Hat Bugzilla – Bug 66387
SMP kernel for dual Xeon "see" four processors
Last modified: 2007-04-18 12:43:03 EDT
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Description of problem:
I have installed RH 7.3 on Tyan i860 dual Xeon motherboard without any
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
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):
Steps to Reproduce:
1. I don't want reinstall RH7.3 and upgrade again the kernel.
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.
no, top doesn't still produce the right info.
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
P.S. I found the answer of my problem in the support database of suse linux.
I am seeing double processors on xeon servers also. My kernel is 2.4.18-10
Does redhat consider this a bug?
you see 4 virtual processors...
you paid money to intel for the hyperthreading feature... use it! :)