Date:   Tue, 21 Feb 2023 10:27:31 +0000
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>
Subject: Re: [PATCH v9 0/8] Parallel CPU bringup for x86_64
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On 21 February 2023 09:49:51 GMT, Oleksandr Natalenko <oleksandr@natalenko=
=2Ename> wrote:
>On 21=2E02=2E2023 10:06, David Woodhouse wrote:
>> Why does arch/x86/kernel/acpi/sleep=2Ec::x86_acpi_suspend_lowlevel() se=
t
>>=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) ?
>
>Wanna me try `initial_gs =3D per_cpu_offset(0);` too?

Hm, yes please=2E There's another one to make zero on the next line up, I =
think?

>> Or maybe we should just set up smpboot_control for the CPU to find its
>> own stuff, *even* on waking=2E Since the structures are already set up,
>> it isn't like a clean boot=2E
>>=20
>> If you let it boot in parallel mode, what if you just *remove* the line
>> that sets smpboot_control=3D0 ?
>
>If the `smpboot_control =3D 0;` line in arch/x86/kernel/acpi/sleep=2Ec::x=
86_acpi_suspend_lowlevel() is commented out, and the system is booted in pa=
rallel mode, then suspend/resume works=2E

Well that's entertaining=2E Now, can we come up with any theory which does=
n't leave us wondering why it ever worked in the first place=2E=2E=2E?