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Xen 7.6 ignoring second processor

jon yeargers


Started working on BIOS updates recently in order to prepare for XS patches and v8. When looking at some system diagnostics I noticed that the number of CPUs in some boxes (2) doesn't match up with what Xen reports from the CLI. Spoke with Dell support about this and was told to get all the BIOS updated and try again. Same issue.


DRAC reports 2 CPUs, 8 cores each with HT enabled. Expecting that OS will report the same.


    [root@xen3 ~]# lscpu | grep Socket

    Socket(s):             1


    [root@xen3 ~]# lscpu | grep Thread

    Thread(s) per core:    2


    [root@xen3 ~]# cat /proc/cpuinfo | grep -i processor | wc -l



    [root@xen3 ~]# dmidecode | grep -i "socket designation"

    Socket Designation: CPU1

    Socket Designation: CPU2


(looking at these settings on a 'standard' Centos 7.x install shows the expected values)


Did I misconfigure Xen 7.6? Some licensing issue? Other?

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Dom0 is set to take up no more than 16 VCPUs, but that's not a limit on the total number of VCPUs available for use by VMs.


The latest security patches will not specifically disable the hyperthreading AFAIK; I thought you had to do that in the BIOS? The hotfix README does say that to be totally effective, hyperthreading has to be disabled.



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If you run "top" and hit "1" do you see all 32 VCPUs? Also, run "xl info –n" and you should see the full CPU topology as to cores and sockets and the assigned CPU.


With "cat /proc/cpuinfo | grep -i processor | wc -l" I see 16 CPUs on one of my boxes, which clearly doesn't including the hyperthreads, as in this case I have actually 32 VCPUs.


I'd trust what you see on the XenServer host itself.



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"top" shows 16 VCPUs


# xl info -n

host                   : xen4

release                : 4.4.0+10

version                : #1 SMP Fri Aug 24 08:15:39 UTC 2018

machine                : x86_64

nr_cpus                : 32

max_cpu_id             : 223

nr_nodes               : 2

cores_per_socket       : 8

threads_per_core       : 2

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