Re: [PATCH v5 0/8] Remove EPYC mode apicid decode and use generic decode

[Igor Mammedov <imammedo@redhat.com>]

On Fri, 21 Aug 2020 17:12:19 -0500
Babu Moger <babu.moger@amd.com> wrote:

> To support some of the complex topology, we introduced EPYC mode apicid decode.
> But, EPYC mode decode is running into problems. Also it can become quite a
> maintenance problem in the future. So, it was decided to remove that code and
> use the generic decode which works for majority of the topology. Most of the
> SPECed configuration would work just fine. With some non-SPECed user inputs,
> it will create some sub-optimal configuration.
> Here is the discussion thread.
> https://lore.kernel.org/qemu-devel/c0bcc1a6-1d84-a6e7-e468-d5b437c1b254@amd.com/
> 
> This series removes all the EPYC mode specific apicid changes and use the generic
> apicid decode.

the main difference between EPYC and all other CPUs is that
it requires numa configuration (it's not optional)
so we need an extra patch on top of this series to enfoce that, i.e:

 if (epyc && !numa) 
    error("EPYC cpu requires numa to be configured")

I think there was a patch in previous revisions that aimed for this.
Simplest form would be above snippet.

More complex one, would be moving auto_enable_numa from MachineClass to
MachineState so we can change it at runtime if EPYC is used. That should
take care of use case where user hasn't provided -numa.


Eduardo,
 is there any way to tell managment that particular CPU type requires
 -numa ?

> ---
> v5:
>  Revert EPYC specific decode.
>  Simplify CPUID_8000_001E
> 
> v4:
>   https://lore.kernel.org/qemu-devel/159744083536.39197.13827776633866601278.stgit@naples-babu.amd.com/
>   Not much of a change. Just added few text changes.
>   Error out configuration instead of warning if dies are not configured in EPYC.
>   Few other text changes to clarify the removal of node_id, nr_nodes and nodes_per_pkg.
> 
> v3:
>   https://lore.kernel.org/qemu-devel/159681772267.9679.1334429994189974662.stgit@naples-babu.amd.com/#r
>   Added a new check to pass the dies for EPYC numa configuration.
>   Added Simplify CPUID_8000_001E patch with some changes suggested by Igor.
>   Dropped the patch to build the topology from CpuInstanceProperties.
>   TODO: Not sure if we still need the Autonuma changes Igor mentioned.
>   Needs more clarity on that.
> 
> v2:
>   https://lore.kernel.org/qemu-devel/159362436285.36204.986406297373871949.stgit@naples-babu.amd.com/
>   Used the numa information from CpuInstanceProperties for building
>   the apic_id suggested by Igor.
>   Also did some minor code re-aarangement to take care of changes.
>   Dropped the patch "Simplify CPUID_8000_001E" from v1. Will send
>   it later.
> 
> v1:
>  https://lore.kernel.org/qemu-devel/159164739269.20543.3074052993891532749.stgit@naples-babu.amd.com
> 
> Babu Moger (8):
>       hw/i386: Remove node_id, nr_nodes and nodes_per_pkg from topology
>       Revert "i386: Fix pkg_id offset for EPYC cpu models"
>       Revert "target/i386: Enable new apic id encoding for EPYC based cpus models"
>       Revert "hw/i386: Move arch_id decode inside x86_cpus_init"
>       Revert "i386: Introduce use_epyc_apic_id_encoding in X86CPUDefinition"
>       Revert "hw/i386: Introduce apicid functions inside X86MachineState"
>       Revert "hw/386: Add EPYC mode topology decoding functions"
>       i386: Simplify CPUID_8000_001E for AMD
> 
> 
>  hw/i386/pc.c               |    8 +--
>  hw/i386/x86.c              |   43 +++-------------
>  include/hw/i386/topology.h |  101 ---------------------------------------
>  include/hw/i386/x86.h      |    9 ---
>  target/i386/cpu.c          |  115 ++++++++++++++++----------------------------
>  target/i386/cpu.h          |    3 -
>  tests/test-x86-cpuid.c     |   40 ++++++++-------
>  7 files changed, 73 insertions(+), 246 deletions(-)
> 
> --
> Signature
>