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I just got a new laptop and installed Ubuntu 19.04, alongside Windows. But it seems to only be using one of my cpu cores while the other cores are doing nothing.

htop core usage

Even after rebooting it keeps using core 5.

Some Debug Information:
Device model: HP Pavilion 15-cs2975nd
Output from lscpu:

Architecture:        x86_64
CPU op-mode(s):      32-bit, 64-bit
Byte Order:          Little Endian
Address sizes:       39 bits physical, 48 bits virtual
CPU(s):              8
On-line CPU(s) list: 0-7
Thread(s) per core:  2
Core(s) per socket:  4
Socket(s):           1
NUMA node(s):        1
Vendor ID:           GenuineIntel
CPU family:          6
Model:               142
Model name:          Intel(R) Core(TM) i7-8565U CPU @ 1.80GHz
Stepping:            11
CPU MHz:             3798.265
CPU max MHz:         4600,0000
CPU min MHz:         400,0000
BogoMIPS:            3984.00
Virtualization:      VT-x
L1d cache:           32K
L1i cache:           32K
L2 cache:            256K
L3 cache:            8192K
NUMA node0 CPU(s):   0-7
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 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 ssbd ibrs ibpb stibp tpr_shadow vnmi flexpriority ept vpid ept_ad fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid mpx rdseed adx smap clflushopt intel_pt xsaveopt xsavec xgetbv1 xsaves dtherm ida arat pln pts hwp hwp_notify hwp_act_window hwp_epp md_clear flush_l1d arch_capabilities

Edit: With a bit of help from ycnz we figured out that the other cores do get up to 100% when running stress but it still seems to favor one core making the UI stutter and run slow.

Jeroen1602
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1 Answers1

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The answer really depends on what you're doing when you see this CPU usage. If you run the top command while you're seeing CPU usage like that in the screenshot, you should see "offending" process first in the list. Most likely it's something that's able to run in only a single thread, hence why its only using one core.

ycnz
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  • Well it's not that I'm running a program that is heavily single-threaded, it's just that it runs everything on that single core. I logged into Ubuntu and had Firefox open (with multiple tabs) but only the one core goes up in usage. – Jeroen1602 Sep 02 '19 at 07:24
  • In the screenshot in your question it looks like there's at least something happening on those other cores. Perhaps you could try running a stress test and see if it can actually max out all 8 cores. `sudo apt install stress` then run it with `stress --cpu 8 --timeout 10s` and keep an eye on `htop` while it runs to see what cores it uses. – ycnz Sep 02 '19 at 08:59
  • You are right that it does use 8 cores when running `stress`, but it seems to prefers filling up core 5 before delegating work to the other cores, making the pc feel very slow. Any idea what could be wrong? – Jeroen1602 Sep 02 '19 at 09:29
  • @Jeroen1602 Does this happen only with Firefox? Have you tried another browser? – BeastOfCaerbannog Sep 02 '19 at 15:04
  • I did some debugging and I found out that if I boot my laptop with the power connected the issues happens, but when I boot my laptop without the power connected it behaves normally. If I plug it in later it doesn't change the behavior just like when I unplug it later. Not sure what to do about it. – Jeroen1602 Sep 02 '19 at 17:00