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ua4000

Member

Registered: 2015-10-14

Posts: 562

powersaving: maxcpus=3 vs. cpu c states

I have an Intel Core i7, with 12 cpu, 6 left after disabling smi, due to the intel vulnerability.

At the moment my work changed - I don't need 6 cpu power.
What is the better way to save more energy:
- taking 3 out of the 6 cpu offline by maxcpus=3 in the kernel command line
- or leave all 6 enabled, but rely on cpu c states

lscpu with maxcpus=3:

Architecture:                    x86_64
CPU op-mode(s):                  32-bit, 64-bit
Byte Order:                      Little Endian
Address sizes:                   46 bits physical, 48 bits virtual
CPU(s):                          6
On-line CPU(s) list:             0-2
Off-line CPU(s) list:            3-5
Thread(s) per core:              1
Core(s) per socket:              3
Socket(s):                       1
NUMA node(s):                    1
Vendor ID:                       GenuineIntel
CPU family:                      6
Model:                           45
Model name:                      Intel(R) Core(TM) i7-3930K CPU @ 3.20GHz
Stepping:                        7
CPU MHz:                         1400.000
CPU max MHz:                     3800,0000
CPU min MHz:                     1200,0000
BogoMIPS:                        6406.30
Virtualization:                  VT-x
L1d cache:                       96 KiB
L1i cache:                       96 KiB
L2 cache:                        768 KiB
L3 cache:                        12 MiB
NUMA node0 CPU(s):               0-2
Vulnerability Itlb multihit:     KVM: Mitigation: VMX disabled
Vulnerability L1tf:              Mitigation; PTE Inversion; VMX conditional cache flushes, SMT disabled
Vulnerability Mds:               Mitigation; Clear CPU buffers; SMT disabled
Vulnerability Meltdown:          Mitigation; PTI
Vulnerability Spec store bypass: Mitigation; Speculative Store Bypass disabled via prctl and seccomp
Vulnerability Spectre v1:        Mitigation; usercopy/swapgs barriers and __user pointer sanitization
Vulnerability Spectre v2:        Mitigation; Full generic retpoline, IBPB conditional, IBRS_FW, STIBP disable
                                 d, RSB filling
Vulnerability Srbds:             Not affected
Vulnerability Tsx async abort:   Not affected
Flags:                           fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clfl
                                 ush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm con
                                 stant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc cpuid ap
                                 erfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdc
                                 m pcid dca sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer aes xsave avx lahf
                                 _lm epb pti ssbd ibrs ibpb stibp tpr_shadow vnmi flexpriority ept vpid xsave
                                 opt dtherm ida arat pln pts md_clear flush_l1d

Thanks!