[pve-devel] [PATCH-SERIES v3 qemu-server/manager/common] add and set x86-64-v2 as default model for new vms and detect best cpumodel

Alexandre Derumier aderumier at odiso.com
Mon May 22 12:25:19 CEST 2023


we used kvm64 as default cpumodel since the begin of proxmox. (basically, it's like a pentium4 cpu flags).

New distros like rhel9 are compiled to use more modern cpu flags.
(and windows already use new flags since year, and we already add some extra cpu flags)

In 2020, AMD, Intel, Red Hat, and SUSE worked together to define
three microarchitecture levels on top of the historical x86-64

  * x86-64-v1: original x86_64 baseline instruction set
  * x86-64-v2: vector instructions up to Streaming SIMD
               Extensions 4.2 (SSE4.2)  and Supplemental
               Streaming SIMD Extensions 3 (SSSE3), the
               POPCNT instruction, and CMPXCHG16B
  * x86-64-v3: vector instructions up to AVX2, MOVBE,
               and additional bit-manipulation instructions.
  * x86-64-v4: vector instructions from some of the
               AVX-512 variants.


This patch series add new models inspired from a patch was found on qemu mailing, but never appplied


In addition to theses model, I have enabled aes too.
I think it's really important, because a lot of users use default values and have
bad performance with ssl and other crypto stuffs.

This was discussed on the qemu mailing

Crypto accelerator caveats

Similarly I'm not a huge fan of leaving out the "aes"
instruction for accelerated crypto, as missing "aes" is
also one of the key factors in making qemu64 a bad choice.

If we include 'aes' in x86-64-v2, then we loose support
for Nehalem hosts.

If we include 'aes' in x86-64-v3 then we further loose
support for Dhyana hosts (an EPYC derived CPU).

Nahelemn is a 2008 cpu, so I think it's ok, we are in 2013 ;)
(and user can disable aes flag in gui too)

That mean than the minimum compatible cpu for v2 is Intel Westmere (2010)
and Amd Bulldozer (2011).

This patch series add new models, and set x86-64-abi2 model as default in pve-manager
wizard only.
(to not break current vm, where kvm64 is the default when cputype is not defined
in configuration)

Additionnaly, it could be great to use a real cpu model when we don't have
mixed intel/amd cluster, to have spectre/meltdown/.... mitigations enabled.

I have added initial code for best model detection based on host cpuflags
vs qemu models flags.

Not yet plugged, I'm not sure what is the best way, only at vm create,
or at vm start to auto upgrade vm cpu to last version ?
I'm not sure with cluster, if user add a new older node.
(vmware have a feature called EVC, compute the best model when node join/leave)

changelog v2:
 - remove qemu patch and implement new models in qemu-server
 - use x86-64-vX instead x86-64-abiX  (less confusing for user)
 - don't expose v4 model for now (need epyc v4 for testing)
 - use add and set x86-64-v2 as default model for new vms

changelog v3:
 - add best cpu model detection from cpu flags && msr
 - pve-common : add optionnal parsing of msr in read_cpuinfo

qemu-server :

Alexandre Derumier (7):
  cpuconfig: add new x86-64-vX models
  cpumodel: add cpu models with flags
  cpumodel: compute qemu supported flags
  cpuconfig: add get_host_cpu_flags
  cpuconfig: add find_best_cpumodel
  cpuconfig: add find_hosts_common_flags
  add best cpu model detection tests

 PVE/QemuServer/CPUConfig.pm |  253 ++-
 PVE/QemuServer/CPUModels.pm | 4221 +++++++++++++++++++++++++++++++++++
 PVE/QemuServer/Makefile     |    1 +
 test/Makefile               |    5 +-
 test/run_cpumodel_tests.pl  |  272 +++
 5 files changed, 4682 insertions(+), 70 deletions(-)
 create mode 100644 PVE/QemuServer/CPUModels.pm
 create mode 100755 test/run_cpumodel_tests.pl


Alexandre Derumier (1):
  read_cpuinfo: add msr support

 src/PVE/ProcFSTools.pm | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)


Alexandre Derumier (1):
  qemu: processor : set x86-64-v2 as default cputype for create wizard

 www/manager6/qemu/OSDefaults.js    |  1 +
 www/manager6/qemu/ProcessorEdit.js | 13 +++++++++++++
 2 files changed, 14 insertions(+)


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