Message-ID: <d91f96eb-86a1-c794-761d-a96e39076b13@bytedance.com>
Date:   Tue, 21 Feb 2023 10:47:31 +0000
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Subject: Re: [External] Re: [PATCH v9 0/8] Parallel CPU bringup for x86_64
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To:     David Woodhouse <dwmw2@infradead.org>,
        Oleksandr Natalenko <oleksandr@natalenko.name>
Cc:     Kim Phillips <kim.phillips@amd.com>, tglx@linutronix.de,
        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>
References: <20230215145425.420125-1-usama.arif@bytedance.com>
 <ed8d662351cfe5793f8cc7e7e8c514d05d16c501.camel@infradead.org>
 <2668869.mvXUDI8C0e@natalenko.name>
 <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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 <ee0d0d971a3095d6a1e96ad4f1ba32d2@natalenko.name>
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From:   Usama Arif <usama.arif@bytedance.com>
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On 21/02/2023 10:27, David Woodhouse wrote:
> 
> 
> On 21 February 2023 09:49:51 GMT, Oleksandr Natalenko <oleksandr@natalenko.name> wrote:
>> On 21.02.2023 10:06, David Woodhouse wrote:
>>> Why does arch/x86/kernel/acpi/sleep.c::x86_acpi_suspend_lowlevel() set
>>>
>>>      initial_gs = per_cpu_offset(smp_processor_id()) ?
>>>
>>> Would it not be CPU#0 that comes back up, and should it not get
>>> per_cpu_offset(0) ?
>>
>> Wanna me try `initial_gs = per_cpu_offset(0);` too?
> 

I think it might be smp_processor_id() and not 0 incase CPU0 was offline 
at the point the system was suspended?

> Hm, yes please. 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. 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=0 ?
>>
>> If the `smpboot_control = 0;` line in arch/x86/kernel/acpi/sleep.c::x86_acpi_suspend_lowlevel() is commented out, and the system is booted in parallel mode, then suspend/resume works.
> 
> Well that's entertaining. Now, can we come up with any theory which doesn't leave us wondering why it ever worked in the first place...?