I have a Linux Machine with 2 X5650 2.7GHZ Processors and I host game servers on it for my gaming community, and there comes my issue:
game servers need best 1 core performance, but I have 24 vCORES and 12 Physical Cores.
Is it possible to "tell" kernel use 12 physical cores? and then 1 physical core will use 2VCORES?

Thanks,
Alex.

You can use taskset to manually distribute processes across cores by setting their thread affinities. To figure out which threads belong to which cores and processors, check /proc/cpuinfo as shown below:

$ grep -E '^processor|^physical id|^core id' /proc/cpuinfo |sed 's/^processor/nprocessor/'



processor       : 0

physical id     : 0

core id         : 0



processor       : 1

physical id     : 0

core id         : 1



processor       : 2

physical id     : 0

core id         : 0



processor       : 3

physical id     : 0

core id         : 1

$ _

processor is the thread number, physical id is the physical CPU number, and core id is the core number. The above output comes from a machine with a single CPU with two cores and four threads.

taskset can be used as taskset --all-tasks -p <hex_mask> <pid> to modify the affinity of all threads of an extant process. The hex_mask is a bitmask where each 1 bit represents an assigned CPU thread and numbering starts from the right. For instance, 0xa for the mask means binary 0b1010 which indicates an affinity of thread #1 and thread #3 for the process. The PID, I hope, is self-explanatory.

Virtual Cores or "Threads"

If you want to avoid virtual cores or "threads", then you could simply disable the feature. Although, disabling this feature not necessarily will improve performance, that depends on the server software you are running (there are engines that work better with HT/SMT, while others don't), you should probably test it.

According to your post, the Intel X5650 has 6 Cores and 12 Threads each. You can verify this with lscpu. For ex. the following CPU has 4 Cores and the HT disabled:

$ lscpu

Architecture:        x86_64

CPU op-mode(s):      32-bit, 64-bit

Byte Order:          Little Endian

CPU(s):              4

On-line CPU(s) list: 0-3

Thread(s) per core:  1

Core(s) per socket:  4

Socket(s):           1

You can verify the HT cores by running:

# grep -H . /sys/devices/system/cpu/cpu*/topology/thread_siblings_list

This will output something like:

$  grep -H . /sys/devices/system/cpu/cpu*/topology/thread_siblings_list

/sys/devices/system/cpu/cpu0/topology/thread_siblings_list:X,Y

/sys/devices/system/cpu/cpu1/topology/thread_siblings_list:X,Y

/sys/devices/system/cpu/cpu2/topology/thread_siblings_list:X,Y

/sys/devices/system/cpu/cpu3/topology/thread_siblings_list:X,Y

Where X,Y are Physical-Core-ID,HT-Core-ID, as in: 0,4 (the first virtual core ID usually is the next to the last physical one).

Disabling Hyper-Threading

With this information you have 2 options to disable the HT, depending on your access to the server:

1. 
   

   Through the BIOS settings (the easiest)

   
   
   
   
   
   • You should check your Motherboard manufacturer manual, and disable the Hyper-Threading there. This requires the server to reboot and access to the BIOS settings.
   
   
   
   


2. 
   

   Through the command line (no need to reboot)

   
   
   
   
   
   • You could disable each virtual core in Linux directly, create a disablevcore.sh file:
   
   
   
   

    #!/bin/bash

    for i in {YY..YY}; do

       echo "Disabling logical HT core $i."

       echo 0 > /sys/devices/system/cpu/cpu${i}/online;

    done

And replace YY..YY for the threads ID you want to disable, according to your processors, probably {6..11}. Although I'm not sure how the numbering works on multi-socket setups, so you should check carefully.

3. 
   

   Another option (2.a if you will) is to disable it in GRUB:

   
   
   
   
   
   • Edit the GRUB config file: /etc/sysconfig/grub (if and append noht in the line that starts with: GRUB_CMDLINE_LINUX. It should be something like this:
   
   
   
   

GRUB_CMDLINE_LINUX="... noht ..."

More about HT and SMT:

Intel "Hyper-Threading"

Hyper-threading is Intel's proprietary simultaneous multithreading
implementation used to improve parallelization of computations
performed on x86 microprocessors. It first appeared in February 2002
on Xeon server processors and in November 2002 on Pentium 4 desktop
CPUs. Later, Intel included this technology in Itanium, Atom, and Core
'i' Series CPUs, among others.

https://en.wikipedia.org/wiki/Hyper-threading

AMD "Simultaneus Multithreading (SMT)"

Simultaneous multithreading is a technique for improving the overall
efficiency of superscalar CPUs with hardware multithreading. SMT
permits multiple independent threads of execution to better utilize
the resources provided by modern processor architectures.

https://en.wikipedia.org/wiki/Simultaneous_multithreading

More details on disabling HT through the kernel:

https://www.golinuxhub.com/2018/01/how-to-disable-or-enable-hyper.html