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I've got an Intel i7 2700k here, and I'd like to know how I can tell which processors are physical and which are virtual (ie: hyperthreading). I'm currently running a Conky script to display my CPU temps, frequencies, and loads, but I'm not sure that I've done it right:

awesome

I've written my own script to get temperatures and frequencies from i7z, but these only correspond to physical cores. I'm currently displaying each core like this:

${cpu cpu1} ${lua display_temp 0} ${lua display_load 0}
${cpu cpu2}
${cpu cpu3} ${lua display_temp 1} ${lua display_load 1}
${cpu cpu4}
# ...

I'm not sure that this is right, because of the loads and temperatures I see sometimes. In /proc/cpuinfo, how are cores sorted? First all physical then all virtual? Each physical core then its virtual core(s)? How are they sorted?

Naftuli Kay
  • 39,676

5 Answers5

22

You can know about each processor core by examining each cpuinfo entry:

processor       : 0
[...]
physical id     : 0
siblings        : 8
core id         : 0
cpu cores       : 4
apicid          : 0

processor       : 1
[...]
physical id     : 0
siblings        : 8
core id         : 1
cpu cores       : 4
apicid          : 2 

processor       : 2
[...]
physical id     : 0
siblings        : 8
core id         : 2
cpu cores       : 4
apicid          : 4 

processor       : 3
[...]
physical id     : 0
siblings        : 8
core id         : 3
cpu cores       : 4
apicid          : 6

processor       : 4
[...]
physical id     : 0
siblings        : 8
core id         : 0
cpu cores       : 4
apicid          : 1

[and so on]

physical id shows the identifier of the processor. Unless you have a multiprocessor setup (having two separate, physical processor in a machine), it will always be 0.

siblings show the number of processor attached to the same physical processor.

core id show the identifier of the current core, out to a total of cpu cores. You can use this information to correlate which virtual processor goes into a single core.

apicid (and original apicid) show the number of the (virtual) processor, as given by the bios.

Note that there 8 siblings and 4 cores, so there is 2 virtual processor per core. There is no distinction between "virtual" or "real" in hyperthreading. But using this information you can associate which processors are from the same core.

Alexander Pozdneev
  • 939
BatchyX
  • 3,063
18

you can also use lscpu:

# lscpu --all --extended
CPU NODE SOCKET CORE L1d:L1i:L2:L3:L4 ONLINE MAXMHZ    MINMHZ
0   0    0      0    0:0:0:0:0        yes    3200.0000 800.0000
1   0    0      1    1:1:1:0:0        yes    3200.0000 800.0000
2   0    0      2    2:2:2:0:0        yes    3200.0000 800.0000
3   0    0      3    3:3:3:0:0        yes    3200.0000 800.0000
4   0    0      0    0:0:0:0:0        yes    3200.0000 800.0000
5   0    0      1    1:1:1:0:0        yes    3200.0000 800.0000
6   0    0      2    2:2:2:0:0        yes    3200.0000 800.0000
7   0    0      3    3:3:3:0:0        yes    3200.0000 800.0000

here logical cores 0 and 4 go to core 0

NickSoft
  • 320
5

The /sys filesystem holds a nice overview of this information. Here is an example from an SMP quadcore box with Hyperthreading:

# grep . /sys/devices/system/cpu/cpu{,1}?/topology/thread_siblings | tr : \\t | sed 's,^,    ,'
/sys/devices/system/cpu/cpu0/topology/thread_siblings   00000000,00000101
/sys/devices/system/cpu/cpu1/topology/thread_siblings   00000000,00000202
/sys/devices/system/cpu/cpu2/topology/thread_siblings   00000000,00000404
/sys/devices/system/cpu/cpu3/topology/thread_siblings   00000000,00000808
/sys/devices/system/cpu/cpu4/topology/thread_siblings   00000000,00001010
/sys/devices/system/cpu/cpu5/topology/thread_siblings   00000000,00002020
/sys/devices/system/cpu/cpu6/topology/thread_siblings   00000000,00004040
/sys/devices/system/cpu/cpu7/topology/thread_siblings   00000000,00008080
/sys/devices/system/cpu/cpu8/topology/thread_siblings   00000000,00000101
/sys/devices/system/cpu/cpu9/topology/thread_siblings   00000000,00000202
/sys/devices/system/cpu/cpu10/topology/thread_siblings  00000000,00000404
/sys/devices/system/cpu/cpu11/topology/thread_siblings  00000000,00000808
/sys/devices/system/cpu/cpu12/topology/thread_siblings  00000000,00001010
/sys/devices/system/cpu/cpu13/topology/thread_siblings  00000000,00002020
/sys/devices/system/cpu/cpu14/topology/thread_siblings  00000000,00004040
/sys/devices/system/cpu/cpu15/topology/thread_siblings  00000000,00008080

Identical content denotes threads of the same core. I.e.

  • cpu0 / cpu8
  • cpu1 / cpu9
  • etc.

There is similar information in the core_siblings pseudo-file, along with yet more topology information.

Felix Frank
  • 196
3

If you see the 'ht' flag in /proc/cpuinfo then you have hyper-threading enabled and each real core is split into multiple threads, there is no concept of real thread and virtual thread: both are effectively virtual.

What you may wish to investigate is comparing cores and sockets, use the 'physical id' topology identifier to group cores together.

Steve-o
  • 420
  • The ht flag only indicates that multi-threading (HTT) is supported by the CPU -- not if it's enabled or not. Even then, it can't always be relied upon, e.g., it falsely indicates that an i5 i5-6500 supports HTT: https://ark.intel.com/content/www/us/en/ark/products/88184/intel-core-i5-6500-processor-6m-cache-up-to-3-60-ghz.html – Anthony Geoghegan Nov 22 '19 at 17:12
2

Previous answer is very interesting.

After some googling, I found some related subjects:

On the last link, the python script does not work when your host have many physical IDs. I tried to modify it with a different condition at the end :

Changing:

if p > 0:

to

if p % 2 == 1:

But it does not work as expected, based on the previous message. By the way, you can do something more comprehensive than:

grep . /sys/devices/system/cpu/cpu{,1}?/topology/thread_siblings | tr : \\\t | sed -r 's,^,\s\s\s\s,'

with:

for file in /sys/devices/system/cpu/cpu[0-9]*/topology/thread_siblings_list; do echo -n "$file "; cat $file; done |sort -k2 -n

[...]

What is interesting on a many cores host with hyperthreading enable is the distribution of logical cores on the hardware.

For instance, on one of my computer (48 logical core, 2 physical processors, 24 (12*2) 'real cores' (so, also 24 virtual cores)) :

for file in /sys/devices/system/cpu/cpu[0-9]*/topology/thread_siblings_list; do echo -n "$file "; cat $file; done |sort -k2 -n

 /sys/devices/system/cpu/cpu0/topology/thread_siblings_list 0,24
 /sys/devices/system/cpu/cpu24/topology/thread_siblings_list 0,24
 /sys/devices/system/cpu/cpu1/topology/thread_siblings_list 1,25
 /sys/devices/system/cpu/cpu25/topology/thread_siblings_list 1,25
 /sys/devices/system/cpu/cpu26/topology/thread_siblings_list 2,26
 /sys/devices/system/cpu/cpu2/topology/thread_siblings_list 2,26
 /sys/devices/system/cpu/cpu27/topology/thread_siblings_list 3,27
 /sys/devices/system/cpu/cpu3/topology/thread_siblings_list 3,27
 /sys/devices/system/cpu/cpu28/topology/thread_siblings_list 4,28
 /sys/devices/system/cpu/cpu4/topology/thread_siblings_list 4,28
 /sys/devices/system/cpu/cpu29/topology/thread_siblings_list 5,29
 /sys/devices/system/cpu/cpu5/topology/thread_siblings_list 5,29
 /sys/devices/system/cpu/cpu30/topology/thread_siblings_list 6,30
 /sys/devices/system/cpu/cpu6/topology/thread_siblings_list 6,30
 /sys/devices/system/cpu/cpu31/topology/thread_siblings_list 7,31
 /sys/devices/system/cpu/cpu7/topology/thread_siblings_list 7,31
 /sys/devices/system/cpu/cpu32/topology/thread_siblings_list 8,32
 /sys/devices/system/cpu/cpu8/topology/thread_siblings_list 8,32
 /sys/devices/system/cpu/cpu33/topology/thread_siblings_list 9,33
 /sys/devices/system/cpu/cpu9/topology/thread_siblings_list 9,33
 /sys/devices/system/cpu/cpu10/topology/thread_siblings_list 10,34
 /sys/devices/system/cpu/cpu34/topology/thread_siblings_list 10,34
 /sys/devices/system/cpu/cpu11/topology/thread_siblings_list 11,35
 /sys/devices/system/cpu/cpu35/topology/thread_siblings_list 11,35
 /sys/devices/system/cpu/cpu12/topology/thread_siblings_list 12,36
 /sys/devices/system/cpu/cpu36/topology/thread_siblings_list 12,36
 /sys/devices/system/cpu/cpu13/topology/thread_siblings_list 13,37
 /sys/devices/system/cpu/cpu37/topology/thread_siblings_list 13,37
 /sys/devices/system/cpu/cpu14/topology/thread_siblings_list 14,38
 /sys/devices/system/cpu/cpu38/topology/thread_siblings_list 14,38
 /sys/devices/system/cpu/cpu15/topology/thread_siblings_list 15,39
 /sys/devices/system/cpu/cpu39/topology/thread_siblings_list 15,39
 /sys/devices/system/cpu/cpu16/topology/thread_siblings_list 16,40
 /sys/devices/system/cpu/cpu40/topology/thread_siblings_list 16,40
 /sys/devices/system/cpu/cpu17/topology/thread_siblings_list 17,41
 /sys/devices/system/cpu/cpu41/topology/thread_siblings_list 17,41
 /sys/devices/system/cpu/cpu18/topology/thread_siblings_list 18,42
 /sys/devices/system/cpu/cpu42/topology/thread_siblings_list 18,42
 /sys/devices/system/cpu/cpu19/topology/thread_siblings_list 19,43
 /sys/devices/system/cpu/cpu43/topology/thread_siblings_list 19,43
 /sys/devices/system/cpu/cpu20/topology/thread_siblings_list 20,44
 /sys/devices/system/cpu/cpu44/topology/thread_siblings_list 20,44
 /sys/devices/system/cpu/cpu21/topology/thread_siblings_list 21,45
 /sys/devices/system/cpu/cpu45/topology/thread_siblings_list 21,45
 /sys/devices/system/cpu/cpu22/topology/thread_siblings_list 22,46
 /sys/devices/system/cpu/cpu46/topology/thread_siblings_list 22,46
 /sys/devices/system/cpu/cpu23/topology/thread_siblings_list 23,47
 /sys/devices/system/cpu/cpu47/topology/thread_siblings_list 23,47

It means cpu0 and cpu24 share the same physical hardware "address". Same thing for cpu1 and cpu25...

So, basically, if I would like to disable hyperthreading from the my linux OS, I should put '0' in cpu{24..47}/online with

for fake_cpu in {24..47}; do echo 0 > /sys/devices/system/cpu/cpu$fake_cpu/online;done

You will notice how interesting my system is numbering the cores.

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remyd1
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