How to check if Hyper Threading (HT) is enabled or disabled on my Linux server

How to check if Hyper Threading (HT) is enabled or disabled on my Linux server

In some online articles I have observed, tells that you can use below commands to validate the status of Hyper Threading

How to check if Hyper Threading (HT) is enabled or disabled on my Linux server
# dmidecode | grep -i HTT
                HTT (Multi-threading)
                HTT (Multi-threading)

Also below command can be used

# cat /proc/cpuinfo | grep -o ht | uniq
ht

Please NOTE the above commands tells us that the server supports hyper threading but it has no information on the current status of hyper threading on that server.

To check if hyper threading is enabled or not first of all you must know about the CPU model you are using, you may need to refer to the CPU vendor's documentation for this information

Using the below command you can find the CPU vendor and model number using which you can easily get the CPU documentation from the vendor page.

# grep "model name" proc/cpuinfo | sort -u
model name      : Intel(R) Xeon(R) CPU E5-2640 v3 @ 2.60GHz

Next you must look out for below information from the CPU documentation, I found mine at Intel® Xeon® Processor E5 v3 Family

How to check if Hyper Threading (HT) is enabled or disabled on my Linux server

Here look out for number of cores the CPU has i.e. no. of threads as it shows below

# of Cores 8
# of Threads 16

So with this we know my CPU has total 16 logical CPUs if HT is not enabled and 32 logical CPUs if HT is enabled

Now lets checking the real stats from the server, 'lscpu' and '/proc/cpuinfo' are the two tools which will help us get this information

Below is my output of lscpu

# lscpu
Architecture:          x86_64
CPU op-mode(s):        32-bit, 64-bit
Byte Order:            Little Endian
CPU(s):                32
On-line CPU(s) list:   0-31
Thread(s) per core:    2
Core(s) per socket:    8
Socket(s):             2
NUMA node(s):          1
Vendor ID:             GenuineIntel
CPU family:            6
Model:                 63
Model name:            Intel(R) Xeon(R) CPU E5-2640 v3 @ 2.60GHz
Stepping:              2
CPU MHz:               2600.000
CPU max MHz:           2600.0000
CPU min MHz:           1200.0000
BogoMIPS:              5193.74
Virtualization:        VT-x
L1d cache:             32K
L1i cache:             32K
L2 cache:              256K
L3 cache:              20480K
NUMA node0 CPU(s):     0-31

Here is my first HINT, it shows we have 2 sockets, 8 cores and 2 thread per core.
That is unlikely and mostly in systems with disabled hyper threading we would get "1 thread per core"

Check the total number of physical CPUs

The following command will show how many active physical processors a system has

# grep physical.id /proc/cpuinfo | sort -u | wc -l
2

Number of cores per CPU

On a system with multi-core processors, the following command should report the number of CPU cores per physical processor (though in rare cases it might not).

Example: If this number is 8 and physical CPUs is 2, then each of the 2 physical processors has 8 CPU cores, leading to a total of 16 cores.

# grep cpu.cores /proc/cpuinfo | sort -u
cpu cores       : 8

We can validate the same using below command, using this we can check the number of cores per physical CPUs
For the first CPU (0)

# cat /proc/cpuinfo | egrep -E "^physical|core id"| xargs -l2 | sort -u | awk -F " " '{print $4}' | grep 0 | wc -l
8

For the second CPU (1)

# cat /proc/cpuinfo | egrep -E "^physical|core id"| xargs -l2 | sort -u | awk -F " " '{print $4}' | grep 1 | wc -l
8

Again coming back to the calculation

For this with 2 physical CPUs(sockets) and 8 cores we would expect 16 logical CPUs if hyper threading is not enabled

# grep processor /proc/cpuinfo | wc -l
32

But here we have 32 CPUs so this clearly stats that hyper threading is enabled.

Lets take an example from another of my server where HT is disabled

# lscpu
Architecture:          x86_64
CPU op-mode(s):        32-bit, 64-bit
Byte Order:            Little Endian
CPU(s):                16
On-line CPU(s) list:   0-15
Thread(s) per core:    1
Core(s) per socket:    8
Socket(s):             2
NUMA node(s):          1
Vendor ID:             GenuineIntel
CPU family:            6
Model:                 63
Model name:            Intel(R) Xeon(R) CPU E5-2640 v3 @ 2.60GHz
Stepping:              2
CPU MHz:               2600.000
CPU max MHz:           2600.0000
CPU min MHz:           1200.0000
BogoMIPS:              5193.67
Virtualization:        VT-x
L1d cache:             32K
L1i cache:             32K
L2 cache:              256K
L3 cache:              20480K
NUMA node0 CPU(s):     0-15

Here as you see "Threads per core" is 1 so this gives us a HINT that there is a possibility that HT is disabled

Check the no of cores
# grep cpu.cores /proc/cpuinfo | sort -u
cpu cores       : 8

Here if we multiply the no of sockets (2) with no of cores (8) then we must have 16 cores if HT is not enabled

# grep processor /proc/cpuinfo | wc -l
16

So we know now HT is disabled on this server.

I hope the article was useful.

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