How do I know which processors are physical cores?

Question

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:

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?

Answer 1

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.

acpiid (and original acpiid) 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.

Answer 2

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.