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Operating Systems Linux Red Hat Lost CPU CORES
# 8  
Old 09-12-2011
RHEL 6.1 x64

TYAN S7010 two E5530 (4 cores each) on RHEL 6.1 x64
# 9  
Old 09-13-2011
Have you checked the output from cpuid and acpidump?
# 10  
Old 09-13-2011
OK, run this command:

zgrep SMP /proc/config.gz

The output should have CONFIG_SMP=y if your SMP support is enabled; that is if your kernel has support for /proc/config.gz. If it does not, there will be an error which tells you nothing.
# 11  
Old 09-13-2011
OBTW, as I recall, most Linux distributions do not come with an SMP enabled kernel; so you will most probably need to create one. Configure a new kernel and answer Y to CONFIG_SMP.
# 12  
Old 09-13-2011
The default kernel for RHEL does include SMP. If someone mucked about, however that could explain it. I would just like to be sure the user is using RHEL 6.1 and not RHAT 6.1.
# 13  
Old 09-13-2011
We can also confirm/check for SMP with uname -a. Here is an example:

$ uname -a
Linux www 2.6.31-15-server #50-Ubuntu SMP Tue Nov 10 15:50:36 UTC 2009 x86_64 GNU/Linux

So, please post the output of uname -a.
# 14  
Old 09-13-2011
Originally Posted by Neo
OK, run this command:
zgrep SMP /proc/config.gz

On Fedora and downstream, the file you probably want is /boot/config-<name of your kernel>. Also CONFIG_SMP is Y by default - at least on AMD64 (x86_64) platforms. For example, I am using 2.6.40 on a F15 X32 development system, so the name of the configuration file is config. (x32 is not a typo, it is a new emerging psABI)

If the OP installs and runs cpuid, we will have a much better idea of what the actual cpus think they are. I suspect that cpuid will return the expected values but I think we should eliminate this possibility or that some cores have been disabled by the BIOS. BTW, There was an interesting discussion on FreeBSD back in 2010 re E5530s and missing cores. Search for "FreeBSD, E5530 cpuid acpidump." Turns out that the missing cores were disabled by a BIOS setting.
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