Message-ID: <85ceb3f92abf3c013924de2f025517372bed19c0.camel@infradead.org>
Subject: Re: [PATCH v9 0/8] Parallel CPU bringup for x86_64
From:   David Woodhouse <dwmw2@infradead.org>
To:     Oleksandr Natalenko <oleksandr@natalenko.name>
Cc:     Kim Phillips <kim.phillips@amd.com>, tglx@linutronix.de,
        Usama Arif <usama.arif@bytedance.com>, arjan@linux.intel.com,
        mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
        hpa@zytor.com, x86@kernel.org, pbonzini@redhat.com,
        paulmck@kernel.org, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org, rcu@vger.kernel.org, mimoja@mimoja.de,
        hewenliang4@huawei.com, thomas.lendacky@amd.com, seanjc@google.com,
        pmenzel@molgen.mpg.de, fam.zheng@bytedance.com,
        punit.agrawal@bytedance.com, simon.evans@bytedance.com,
        liangma@liangbit.com,
        "Limonciello, Mario" <Mario.Limonciello@amd.com>,
        Piotr Gorski <piotrgorski@cachyos.org>
Date:   Tue, 21 Feb 2023 09:06:01 +0000
In-Reply-To: <ce731b5a4a53680b4840467977b33d9a@natalenko.name>
References: <20230215145425.420125-1-usama.arif@bytedance.com>
         <2668799.mvXUDI8C0e@natalenko.name>
         <ed8d662351cfe5793f8cc7e7e8c514d05d16c501.camel@infradead.org>
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         <2a67f6cf18dd2c1879fad9fd8a28242918d3e5d2.camel@infradead.org>
         <982e1d6140705414e8fd60b990bd259a@natalenko.name>
         <715CBABF-4017-4784-8F30-5386F1524830@infradead.org>
         <67dbc69f-b712-8971-f1c9-5d07f506a19c@amd.com>
         <42dc683e2846ae8fc1e09715aaf7884660e1a386.camel@infradead.org>
         <37c18c3aeea2e558633b6da6886111d0@natalenko.name>
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         <3d8ed6e157df10c5175c636de0e21849@natalenko.name>
         <5c557f9b6f55dc2a612ee89142971298e6ae12d8.camel@infradead.org>
         <ee0d0d971a3095d6a1e96ad4f1ba32d2@natalenko.name>
         <5b8f9c89f7015fa80c966c6c7f6fa259db6744f8.camel@infradead.org>
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On Tue, 2023-02-21 at 09:44 +0100, Oleksandr Natalenko wrote:
> On 21.02.2023 09:35, David Woodhouse wrote:
> > On Tue, 2023-02-21 at 09:25 +0100, Oleksandr Natalenko wrote:
> > >=20
> > >=20
> > > Right, sorry. Here it is: http://ix.io/4oLq
> >=20
> > $ echo `grep ^00000001 4oLq=C2=A0 | cut -c36-37`
> > 00 02 04 06 08 0a 0c 0e 10 12 14 16 18 1a 1c 1e 01 03 05 07 09 0b 0d 0f
> > 11 13 15 17 19 1b 1d 1f
> >=20
> > Well they look sane enough. All even APIC IDs and then all the odd ones
> > is a topology that isn't massively surprising.
> >=20
> > Does it match what you get *before* suspend/resume?
>=20
> Yes, the output is completely the same after a fresh boot and after a
> suspend/resume cycle.
>=20
> > Obviously we could stick our fingers in our ears and go "la la la" and
> > just disable it for non-X2APIC, for AMD without X2APIC, or perhaps
> > disable it on *resume* but still use it at boot. But I'd really like to
> > understand what's going on and not do voodoo. Thanks for helping!
>=20

Hm...

Why does arch/x86/kernel/acpi/sleep.c::x86_acpi_suspend_lowlevel() set=20

    initial_gs =3D per_cpu_offset(smp_processor_id()) ?=20

Would it not be CPU#0 that comes back up, and should it not get
per_cpu_offset(0) ?=20

Or maybe we should just set up smpboot_control for the CPU to find its
own stuff, *even* on waking. Since the structures are already set up,
it isn't like a clean boot.

If you let it boot in parallel mode, what if you just *remove* the line
that sets smpboot_control=3D0 ?=20


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