I recently got a new Thinkpad T570. I'm running Fedora 27. It has a i7-7600U processor that should have 2 cores and 4 thread according to Intel (https://ark.intel.com/products/97466/Intel-Core-i7-7600U-Processor-4M-Cache-up-to-3_90-GHz). However, when I run lscpu it shows 2 cores and 2 threads.

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:  2
Core(s) per socket:  2
Socket(s):           1
NUMA node(s):        1
Vendor ID:           GenuineIntel
CPU family:          6
Model:               142
Model name:          Intel(R) Core(TM) i7-7600U CPU @ 2.80GHz
Stepping:            9
CPU MHz:             2900.000
CPU max MHz:         3900.0000
CPU min MHz:         400.0000
BogoMIPS:            5808.00
Virtualization:      VT-x
L1d cache:           32K
L1i cache:           32K
L2 cache:            256K
L3 cache:            4096K
NUMA node0 CPU(s):   0-3
Flags:               fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc art arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc cpuid aperfmperf tsc_known_freq pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 sdbg fma cx16 xtpr pdcm pcid sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer aes xsave avx f16c rdrand lahf_lm abm 3dnowprefetch cpuid_fault epb invpcid_single pti intel_pt tpr_shadow vnmi flexpriority ept vpid fsgsbase tsc_adjust bmi1 hle avx2 smep bmi2 erms invpcid rtm mpx rdseed adx smap clflushopt xsaveopt xsavec xgetbv1 xsaves dtherm ida arat pln pts hwp hwp_notify hwp_act_window hwp_epp

What happened to the other two threads? Is there something I can do to enable these additional threads?

  • 2
    Where are you getting "2 cores and 2 threads"? It says "4" CPUs. It also says "2" threads per core and "2" cores per socket. (threads per core) x (cores per socket) = (threads per socket). 2 x 2 = 4.
    – Bob
    Jan 12 '18 at 2:05
  • That's correct. Maybe my wording was confusing. The problem is that the specification (see link) says it should have 2 cores and 4 threads per core. 2x4=8. It should say 8 CPUs. Jan 12 '18 at 2:09
  • Nope. The Intel spec lists the total number of threads on the chip. Not threads per core.
    – Bob
    Jan 12 '18 at 2:11
  • Bob, unless they changed the way they have been doing things for the last 8 years, that isn't correct. I've had two machines over that time that reported 8 CPUs when Intel says it has 2 cores and 4 threads. Jan 12 '18 at 2:16
  • As a simple sanity test, there does not exist a mainstream x86 CPU that has more than 2 threads per core, much less on a laptop. Unless you're rocking a $6000 Xeon Phi with 72 cores in said laptop.
    – Bob
    Jan 12 '18 at 2:16

Your system has 4 logical processors:

CPU(s):              4

This is the result of having 2 processor cores, each with 2 hardware threads from Intel Hyper-Threading Technology:

Thread(s) per core:  2
Core(s) per socket:  2

The number of threads listed on the Intel ARK page is the total number of hardware threads the processor has. The value listed by lscpu is the number of threads per core.

In short, your system is seeing all of the threads on the physical processor.

  • “A Thread, or thread of execution, is a software term for the basic ordered sequence of instructions that can be passed through or processed by a single CPU core.” - The specifications for your CPU indicates your processor can execute 4 threads. Your processor also has 2 cores. Which means two of those cores is a virtual core (i.e. Intel® Hyper-Threading Technology). I see I am saying the same thing just a different way.
    – Ramhound
    Jan 12 '18 at 2:54
  • I read that description as well, but I interpreted it differently. To me it sounds like they are describing a "single CPU core". I then expect that the number next to "Threads" refers to a "single CPU core" and I should multiply threads and cores to get the number of logical CPUs. Based on what my machines have been reporting for years, that interpretation seemed to be validated. Jan 12 '18 at 3:05
  • You have convinced me that what I saw for years was the result of some kind of bug. I'm still curious about how it seemed to use 8 logical CPUs when only 4 was supposedly possible, but for now I consider this resolved. Thanks for you help and your patience. Jan 12 '18 at 3:09

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