On 13.01.22 01:41, Igor Cicimov wrote:
> Hi,
>
> On 13 Jan 2022 07:33, basti <mailingl...@unix-solution.de> wrote:
>
> Hello,
>
> first of all the most modern CPU in the last 10 years (I gues) use so
> called speed-stepping.
>
> As I can see I was wondering why that speed stepping is not set in a
> KVM
> guest, even if I use "host-passthrough" in the cpu config of the guest.
>
> virsh dumpxml almalinux | grep -i cpu
> <vcpu placement='static'>2</vcpu>
> <cpu mode='host-passthrough' check='none' migratable='on'/>
>
> The cpu on the "host" is:
>
> root@q2:~# lscpu
> Architecture: x86_64
> CPU op-mode(s): 32-bit, 64-bit
> Byte Order: Little Endian
> Address sizes: 36 bits physical, 48 bits virtual
> CPU(s): 4
> On-line CPU(s) list: 0-3
> Thread(s) per core: 1
> Core(s) per socket: 4
> Socket(s): 1
> NUMA node(s): 1
> Vendor ID: GenuineIntel
> CPU family: 6
> Model: 76
> Model name: Intel(R) Celeron(R) CPU N3160 @
> 1.60GHz
> Stepping: 4
> CPU MHz: 480.096
> CPU max MHz: 2240.0000
> CPU min MHz: 480.0000
> BogoMIPS: 3200.00
> Virtualization: VT-x
> L1d cache: 96 KiB
> L1i cache: 128 KiB
> L2 cache: 2 MiB
> NUMA node0 CPU(s): 0-3
> Vulnerability Itlb multihit: Not affected
> Vulnerability L1tf: Not affected
> Vulnerability Mds: Vulnerable: Clear CPU buffers
> attempted, no microcode; SMT disabled
> Vulnerability Meltdown: Mitigation; PTI
> Vulnerability Spec store bypass: Not affected
> 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 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 rdtsc
> p lm constant_tsc arch_perfmon pebs
> bts
> rep_good nopl xtopology tsc_reliable nonstop_tsc cpuid aperfmperf
> tsc_known_freq pni pclmulqdq d
> tes64 monitor ds_cpl vmx est tm2 ssse3
> cx16 xtpr pdcm sse4_1 sse4_2 movbe popcnt tsc_deadline_timer aes rdrand
> lahf_lm 3dnowprefetch epb
> pti tpr_shadow vnmi flexpriority ept
> vpid tsc_adjust smep erms dtherm ida arat
> root@q2:~#
>
> So the max cpu speed should be 2240 MHz.
>
> On the guest it is:
>
> [root@almalinux ~]# lscpu
> Architektur: x86_64
> CPU Operationsmodus: 32-bit, 64-bit
> Byte-Reihenfolge: Little Endian
> CPU(s): 2
> Liste der Online-CPU(s): 0,1
> Thread(s) pro Kern: 1
> Kern(e) pro Socket: 1
> Sockel: 2
> NUMA-Knoten: 1
> Anbieterkennung: GenuineIntel
> BIOS Vendor ID: QEMU
> Prozessorfamilie: 6
> Modell: 76
> Modellname: Intel(R) Celeron(R) CPU N3160 @ 1.60GHz
> BIOS Model name: pc-i440fx-3.1
> Stepping: 4
> CPU MHz: 1600.000
> BogoMIPS: 3200.00
> Virtualisierung: VT-x
> Hypervisor-Anbieter: KVM
> Virtualisierungstyp: voll
> L1d Cache: 32K
> L1i Cache: 32K
> L2 Cache: 4096K
> L3 Cache: 16384K
> NUMA-Knoten0 CPU(s): 0,1
> Markierungen: fpu vme de pse tsc msr pae mce cx8 apic sep
> mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ss syscall nx
> rdtscp lm constant_tsc arch_perfmon rep_good nopl xtopology cpuid
> tsc_known_freq pni pclmulqdq vmx ssse3 cx16 pdcm sse4_1 sse4_2 x2apic
> movbe popcnt tsc_deadline_timer aes rdrand hypervisor lahf_lm
> 3dnowprefetch cpuid_fault pti tpr_shadow vnmi flexpriority ept vpid
> tsc_adjust smep erms arat umip arch_capabilities
>
> So I can't use the 2240 MHz in the guest.
> When I set the cpu governor to "performance" on the host, it doesn't
> matter. The host only see 1600 MHz.
>
> What's wrong there and how should I fix this?
>
> Might be related to cpufreq daemon, what does cpufreq-info command on
> the host say? The cpu freq would dynamically scale on the host so if the
> guest is idle then it will have lower freq allocated. The parameters for
> the cpufreq governor are under /sys/devices/system/cpu/cpufreq/ in case
> you want to play with the config.
On the host all is fine.
The Problem seem to be the guest, the cpu freq would *not* dynamically
scale on it.
I found this: https://bugzilla.redhat.com/show_bug.cgi?id=670104
On the host and on the guest I see constant_tsc in the cpu flags.
