Re: [PATCH v4 2/2] x86/amd: Fixup cpu_core_id for family17h downcore configuration

[Suravee Suthikulpanit]

Boris,

On 7/25/17 12:56, Borislav Petkov wrote:
> On Tue, Jul 25, 2017 at 12:51:53PM +0700, Suravee Suthikulpanit wrote:
> > Ok. Sure, it doesn't need be contiguous. But at least the cpu_core_id should
> > represent an ID that make some sense since it is used in the
> > arch/x86/kernel/smpboot.c: match_smt() and some other places. So, if it's
> > invalid for the downcore configuration (i.e. duplicated where it should not
> > be), we should at least clean this up.
> Ah right, we do use it for the SMT siblings. So yes, it should be
> correct for them. And I'm pretty sure the numbers we derive from the
> initial APIC ID are already good enough for that.

commit 08b259631b5a1d912af4832847b5642f377d9101
Author: Yazen Ghannam <Yazen.Ghannam@xxxxxxx>
Date:   Sun Feb 5 11:50:22 2017 +0100

    x86/CPU/AMD: Fix Zen SMT topology

    After:

      a33d331761bc ("x86/CPU/AMD: Fix Bulldozer topology")

    our  SMT scheduling topology for Fam17h systems is broken, because
    the ThreadId is included in the ApicId when SMT is enabled.

    So, without further decoding cpu_core_id is unique for each thread
    rather than the same for threads on the same core. This didn't affect
    systems with SMT disabled. Make cpu_core_id be what it is defined to be.

Actually, this commit change how we derive the cpu_core_id fro family17h to use 
CPUID_Fn8000001E_EBX instead of from APIC ID for family17h and later.

Thanks,
Suravee