linux-kernel - Re: [patch V3 00/40] x86/cpu: Rework the topology evaluation

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Date:   Wed, 2 Aug 2023 13:56:38 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, Tom Lendacky <thomas.lendacky@....com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Huang Rui <ray.huang@....com>,
        Dimitri Sivanich <dimitri.sivanich@....com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>
Subject: Re: [patch V3 00/40] x86/cpu: Rework the topology evaluation

On 02.08.23 12:20, Thomas Gleixner wrote:
> Hi!
> 
> This is the follow up to V2:
> 
>    https://lore.kernel.org/lkml/20230728105650.565799744@linutronix.de
> 
> which addresses the review feedback and some fallout reported on and
> off-list.
> 
> TLDR:
> 
> This reworks the way how topology information is evaluated via CPUID
> in preparation for a larger topology management overhaul to address
> shortcomings of the current code vs. hybrid systems and systems which make
> use of the extended topology domains in leaf 0x1f. Aside of that it's an
> overdue spring cleaning to get rid of accumulated layers of duct tape and
> haywire.
> 
> What changed vs. V2:
> 
>    - Decoded and fixed the fallout vs. XEN/PV reported by Juergen. Thanks to
>      Juergen for the remote hand debugging sessions!
> 
>      That's addressed in the first two new patches in this series. Summary:
>      XEN/PV booted by pure chance since the addition of SMT control 5 years
>      ago.
> 
>    - Fixed the off by one in the AMD parser which was debugged by Michael
> 
>    - Addressed review comments from various people
> 
> As discussed in:
> 
>    https://lore.kernel.org/lkml/BYAPR21MB16889FD224344B1B28BE22A1D705A@BYAPR21MB1688.namprd21.prod.outlook.com
>    ....
>    https://lore.kernel.org/lkml/87r0omjt8c.ffs@tglx
> 
> this series unfortunately brings the Hyper-V BIOS inconsistency into
> effect, which results in a slight performance impact. The L3 association
> which "worked" so far by exploiting the inconsistency of the Linux topology
> code is not longer supportable as we really need to get the actual short
> comings of our topology management addressed in a consistent way.
> 
> The series is based on V3 of the APIC cleanup series:
> 
>    https://lore.kernel.org/lkml/20230801103042.936020332@linutronix.de
> 
> and also available on top of that from git:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/tglx/devel.git topo-cpuid-v3
> 
> Thanks,
> 
> 	tglx

For Xen PV (dom0 and unprivileged guest):

Tested-by: Juergen Gross <jgross@...e.com>


Juergen


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