KVM with 1 vCPU has CPU load above 1

I have a KVM running with 1 vCPU on a machine with 4 cores.

lscpu in the KVM gives me 1 CPU with 1 core :

Architecture:                    x86_64
CPU op-mode(s):                  32-bit, 64-bit
Byte Order:                      Little Endian
Address sizes:                   43 bits physical, 48 bits virtual
CPU(s):                          1
On-line CPU(s) list:             0
Thread(s) per core:              1
Core(s) per socket:              1
Socket(s):                       1
NUMA node(s):                    1
Vendor ID:                       GenuineIntel
CPU family:                      6
Model:                           13
Model name:                      QEMU Virtual CPU version 2.5+
Stepping:                        3
CPU MHz:                         2300.000
BogoMIPS:                        4600.00
Hypervisor vendor:               KVM
Virtualization type:             full
L1d cache:                       32 KiB
L1i cache:                       32 KiB
L2 cache:                        4 MiB
L3 cache:                        16 MiB
NUMA node0 CPU(s):               0
Vulnerability Itlb multihit:     KVM: Vulnerable
Vulnerability L1tf:              Mitigation; PTE Inversion
Vulnerability Mds:               Vulnerable: Clear CPU buffers attempted, no microcode; SMT Host state unknown
Vulnerability Meltdown:          Mitigation; PTI
Vulnerability Spec store bypass: Vulnerable
Vulnerability Spectre v1:        Mitigation; usercopy/swapgs barriers and __user pointer sanitization
Vulnerability Spectre v2:        Mitigation; Full generic retpoline, STIBP disabled, RSB filling
Vulnerability Srbds:             Not affected
Vulnerability Tsx async abort:   Not affected
Flags:                           fpu de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pse36 clflush mmx fxsr sse sse2 syscall nx lm rep_good nopl xtopology cpuid tsc_known_freq pni cx16
                                  x2apic hypervisor lahf_lm cpuid_fault pti

But when I run top in the KVM, the load average sometimes go above 2 or 3 as if my KVM had more than 1 core. Why is that ? Is there a way to correct the load displayed by top so that it's coherent with the 1 vCPU of the KVM ?

Solution 1:

Load average is proportional to the number of tasks running or ready to run. It does not reflect the number of CPUs.

Indirectly, you can use this to calculate a utilization metric. What the ratio of load average to CPUs means is workload dependent. Some compute heavily applications will have poor response time when this exceeds 1. Others can tolerate a bit higher. Hosts under extreme conditions can get to tens or more without completely seizing up.