[fChk]

In this post we'll talk a bit about QEMU/KVM guest CPUs used in VirMach VPS-9(s) before ending with the right virt-install command that will approximate the CPU model used in Phoenix VPS-9.

To make the case, i'll use the already published data of 3 VPS-9 (Atlanta, L.A., Seattle.) I'll also use my own -still unpublished- data on VPS-9 @Phoenix and @Buffalo.

1-VPS-9 Used Guest CPUs:
From the available data, we have:

1.1- VPS 9 (Atlanta)
https://post4vps.com/Thread-Virmach-VPS-...-Dream-VPS

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Processor       : QEMU Virtual CPU version (cpu64-rhel6)
CPU Cores       : 2 @ 2499.998 MHz
Kernel          : 3.10.0-1062.18.1.el7.x86_64

Geekbench 5.0.1 ( https://browser.geekbench.com/v5/cpu/2472702 )
  -Single-Core Score  : 316
  -Multi-Core score   : 414

System Benchmarks Index Score  x1                                       250.8
System Benchmarks Index Score  x2                                       348.4

1.2- VPS 9 (L.A.)
https://post4vps.com/Thread-Virmach-VPS-9-Review

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Processor  : Intel Xeon E312xx (Sandy Bridge, IBRS update)
CPU cores  : 2 @ 2499.998 MHz
Kernel          : ?

Geekbench 5.3.1 ( https://browser.geekbench.com/v5/cpu/5391725 )
  -Single-Core Score  : 376
  -Multi-Core score   : 646

1.3- VPS 9 (Seattle)
https://post4vps.com/Thread-Virmach-VPS-...ew-Seattle

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Processor  : Intel® Xeon® CPU E5-2670 v2 @ 2.50GHz
CPU Cores       : 2@ 2499.998 MHz
Kernel          : 3.10.0-1062.4.1.el7.x86_64

Geekbench 5.1.0 ( https://browser.geekbench.com/v5/cpu/2077291 )
  -Single-Core Score  : 387
  -Multi-Core score   : 702

System Benchmarks Index Score  x2                                       664.6

1.4- VPS 9 (Phoenix)
Unpublished__data

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Processor  : Intel(R) Xeon(R) CPU E5-2620 v3 @ 2.40GHz
CPU cores  : 2 @ 2399.996 MHz
Kernel        : 4.18.0-147.8.1.el8_1.x86_64

Scores for GeekBench 5.1.1, 5.1.0 and 4.3.1, in single and multi-core tests:
>> GeekBench 5.1.1 :  368 ;   572
>> GeekBench 5.1.0 :  392 ;   651
>> GeekBench 4.3.1 : 1797 ;  2701

UnixBench (2)
System Benchmarks Index Score  x1                                      479.3
System Benchmarks Index Score  x2                                          -

1.5- VPS 9 (Buffalo)
Unpublished__data

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Processor    : Intel(R) Xeon(R) CPU E5-2670 v2 @ 2.50GHz
CPU Cores    : 2 @ 2499.998 MHz
Kernel        : 4.18.0-240.1.1.el8_3.x86_64

Scores for GeekBench 5.1.1, 5.1.0 and 4.3.1, in single and multi-core tests:
>> GeekBench 5.1.1 :  367 ;   646 (https://browser.geekbench.com/v5/cpu/6320829)
>> GeekBench 5.1.0 :  396 ;   654 (https://browser.geekbench.com/v5/cpu/6321825)
>> GeekBench 4.3.1 : 1931 ;  2995 (https://browser.geekbench.com/v4/cpu/16028249)

UnixBench (2)
System Benchmarks Index Score  x1                                      436.0
System Benchmarks Index Score  x2                                      837.7

2- Libvirt CPU Models :
Libvirt supports three ways to configure guests CPU models:

• Host passthrough - In this mode, the host CPU model, stepping, and features are faithfully passed to the guest while certain CPU features will still be filtered out by the hypervisor. This guest CPU model is the recommended CPU to use when live migration isn't needed.
  This mode was used for VPS-9 @Phoenix, @Buffalo and @Seattle.
  
• Named models - This is a set of predefined named CPU models supported by QEMU and that correspond to specific generations of CPUs released by hardware vendors. These named CPUs are typically used when live migration between hosts with differing hardware is mission critical.
  This mode was used for VPS-9 @Atlanta.
  
• Host model - This is the default mode of libvirt that tries to use QEMU's "Named models" to automatically chose a CPU model that is as close to the host CPU as possible while adding any extra flag optimising both host CPU matching and VM live migration.
  This mode was used for VPS-9 @L.A.
  

Armed with the above information in mind, we're now in a position to fine-tune our virt-install command even further, like so:

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virt-install  --virt-type=kvm --hvm --arch=x86_64 --machine=pc \
--name=centos8Phoenix \
--os-type=linux --os-variant=centos8 \
--ram=8192 --vcpus=2 --cpu host-passthrough \
--disk path=/media/phoenix.img \
--import

Again, why is it important to add the cpu flag in the command?.. Answer, to avoid ending up with a host-model CPU (on my system, it's Model: IvyBridge-IBRS that resolve to : Intel Xeon E3-12xx v2 inside the guest) instead of the more powerful host-passthrough model that will resolve to your own host CPU (ie Intel® Core™ i5-3470 CPU @ 3.20GHz on my KVM system.)

In the next post we'll talk a bit about disk I/O fine-tuning.