finding cpu core information in redhat Linux

manoj.linux · 08-18-2009, 01:16 PM

Hi,

I want to know how to find out no of cores in linux.

I have given the command more /proc/cpuinfo

NOw I want to know what is diffrence between cpu cores and core id?

How to find out exact no of cores?

Regards,

Manoj

MensaWater · 08-18-2009, 02:27 PM

You could do the following:

Code:

egrep "^processor|^cpu cores|^core id" /proc/cpuinfo

This should output something like this:
processor : 0
core id : 0
cpu cores : 2
processor : 1
core id : 0
cpu cores : 2
processor : 2
core id : 0
cpu cores : 2
processor : 3
core id : 0
cpu cores : 2
processor : 4
core id : 1
cpu cores : 2
processor : 5
core id : 1
cpu cores : 2
processor : 6
core id : 1
cpu cores : 2
processor : 7
core id : 1
cpu cores : 2

The processor number is an increment of the total number of cores on the system - since I have 0 through 7 it tells me I have 8 cores.

Since the cpu cores tells me I have 2 I know each of my processors is actually dual core. Unfortunately the second core of each processor shows up as if it were a new processor (that is to say core ID 1 on each of processor's 4 through 7 are actually the second cores on each of processor's 0 through 3 (which each show core ID 0).

All of this lets me know I have 4 dual core processors for a total of 8 cores.

By the way dmidecode command will give you a lot more information about things. If in doubt you can always search for the processor model at the vendor's site to see what its specs are.

vikas027 · 05-14-2010, 04:12 AM

Dear All,

I checked two of the Linux Machines and in both of them "core id" is missing from /proc/cpuinfo.
Any idea, why is it so ? Any alternative to find "core id"

Please see the below logs

Code:

-sh-3.00$ cat /etc/redhat-release 
Red Hat Enterprise Linux ES release 4 (Nahant Update 6)
-sh-3.00$ 
-sh-3.00$ egrep "^processor|^cpu cores|^core id" /proc/cpuinfo
processor    : 0
processor    : 1
-sh-3.00$

AND

Code:

[root@server ~]# cat /etc/redhat-release
Red Hat Enterprise Linux Server release 5 (Tikanga)
[root@server ~]#
[root@server ~]# egrep "^processor|^cpu cores|^core id" /proc/cpuinfo
processor       : 0
[root@server ~]#

MensaWater · 05-14-2010, 07:42 AM

If they are single core CPUs then you wouldn't see core ID for them as there is no need to differentiate.

For example I have an older Dell PE 2450 with two single core processors that shows:
egrep "^processor|^cpu cores|^core id" /proc/cpuinfo
processor : 0
processor : 1

Whereas on a newer much larger server with several multicore CPUs I see:
egrep "^processor|^cpu cores|^core id" /proc/cpuinfo
processor : 0
core id : 0
cpu cores : 4
processor : 1
core id : 0
cpu cores : 4
processor : 2
core id : 1
cpu cores : 4
processor : 3
core id : 1
cpu cores : 4
processor : 4
core id : 2
cpu cores : 4
processor : 5
core id : 2
cpu cores : 4
processor : 6
core id : 3
cpu cores : 4
processor : 7
core id : 3
cpu cores : 4
processor : 8
core id : 0
cpu cores : 4
processor : 9
core id : 0
cpu cores : 4
processor : 10
core id : 1
cpu cores : 4
processor : 11
core id : 1
cpu cores : 4
processor : 12
core id : 2
cpu cores : 4
processor : 13
core id : 2
cpu cores : 4
processor : 14
core id : 3
cpu cores : 4
processor : 15
core id : 3
cpu cores : 4

Also after my post last year I've since found the reason for additional CPUs being reported on some servers is due to hyperthreading being enabled. When it is you'll see twice as many processors as you actually have.

As mentioned previously if you use dmidecode to get exact CPU info you may be able to determine from manufacturer's web site what the characteristics (number of cores etc...) are for that model. However, I have noticed Intel seems to have removed a lot of info on older processors.

vikas027 · 05-14-2010, 08:29 AM

Thanks for the valuable information MensaWater.