From: David Woodhouse <dwmw2@infradead.org>
To: Usama Arif <usama.arif@bytedance.com>,
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>
Subject: Re: [External] Re: [PATCH v9 0/8] Parallel CPU bringup for x86_64
Date: Tue, 21 Feb 2023 13:22:20 +0000 [thread overview]
Message-ID: <d081ffa14a8c1f9f68e393a56520da764721a110.camel@infradead.org> (raw)
In-Reply-To: <049adfae-f4a0-349e-323a-52299969ef99@bytedance.com>
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On Tue, 2023-02-21 at 11:54 +0000, Usama Arif wrote:
>
>
> On 21/02/2023 11:42, Oleksandr Natalenko wrote:
> > On 21.02.2023 11:47, Usama Arif wrote:
> > > 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?
> >
> > Is it even possible for CPU 0 to be offline, at least on x86?
> >
>
> It is possible on x86 (using BOOTPARAM_HOTPLUG_CPU0), but I just read
> the Kconfig option and it says:
>
> "resume from hibernate or suspend always starts from CPU0.
> So hibernate and suspend are prevented if CPU0 is offline."
>
> so I guess switching to 0 should be ok.
The interesting question is who ends up using whose stack?
Leaving smpboot_control alone (for the parallel case only; we can't
just leave it with the APIC ID of the last CPU started in the serial
case) will make each CPU find the same CPU# and stack it used to have,
from its own APIC ID and the cpuid_to_apicid[] table.
I don't really grok what's happening in the non-parallel case. We leave
behind the stack for the CPU that happens to be running the suspend
function. And then whichever CPU comes back, it'll get *that* stack.
I don't understand why the parallel bringup changes this. Does the
cpuid to apicid mapping *change* on resume, if the suspending and
resuming CPU are different? Do they swap stacks and CPU# somehow?
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next prev parent reply other threads:[~2023-02-21 13:23 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-02-15 14:54 [PATCH v9 0/8] Parallel CPU bringup for x86_64 Usama Arif
2023-02-15 14:54 ` [PATCH v9 1/8] x86/apic/x2apic: Allow CPU cluster_mask to be populated in parallel Usama Arif
2023-02-16 20:58 ` Kim Phillips
2023-02-15 14:54 ` [PATCH v9 2/8] cpu/hotplug: Move idle_thread_get() to <linux/smpboot.h> Usama Arif
2023-02-15 14:54 ` [PATCH v9 3/8] cpu/hotplug: Add dynamic parallel bringup states before CPUHP_BRINGUP_CPU Usama Arif
2023-02-15 14:54 ` [PATCH v9 4/8] x86/smpboot: Reference count on smpboot_setup_warm_reset_vector() Usama Arif
2023-02-15 14:54 ` [PATCH v9 5/8] x86/smpboot: Split up native_cpu_up into separate phases and document them Usama Arif
2023-02-15 14:54 ` [PATCH v9 6/8] x86/smpboot: Support parallel startup of secondary CPUs Usama Arif
2023-02-15 14:54 ` [PATCH v9 7/8] x86/smpboot: Send INIT/SIPI/SIPI to secondary CPUs in parallel Usama Arif
2023-02-15 14:54 ` [PATCH v9 8/8] x86/smpboot: Serialize topology updates for secondary bringup Usama Arif
2023-02-16 6:34 ` [PATCH v9 0/8] Parallel CPU bringup for x86_64 Paul E. McKenney
2023-02-20 16:08 ` Oleksandr Natalenko
2023-02-20 16:20 ` David Woodhouse
2023-02-20 16:40 ` Oleksandr Natalenko
2023-02-20 20:31 ` David Woodhouse
2023-02-20 21:23 ` Oleksandr Natalenko
2023-02-20 21:34 ` Piotr Gorski
2023-02-20 21:39 ` David Woodhouse
2023-02-20 23:23 ` Kim Phillips
2023-02-20 23:30 ` David Woodhouse
2023-02-21 4:20 ` Kim Phillips
2023-02-21 7:16 ` David Woodhouse
2023-02-21 7:27 ` Oleksandr Natalenko
2023-02-21 7:53 ` David Woodhouse
2023-02-21 8:05 ` Oleksandr Natalenko
2023-02-21 8:17 ` David Woodhouse
2023-02-21 8:25 ` Oleksandr Natalenko
2023-02-21 8:35 ` David Woodhouse
2023-02-21 8:44 ` Oleksandr Natalenko
2023-02-21 9:06 ` David Woodhouse
2023-02-21 9:49 ` Oleksandr Natalenko
2023-02-21 10:27 ` David Woodhouse
2023-02-21 10:47 ` [External] " Usama Arif
2023-02-21 11:42 ` Oleksandr Natalenko
2023-02-21 11:54 ` Usama Arif
2023-02-21 13:22 ` David Woodhouse [this message]
2023-02-21 11:46 ` Oleksandr Natalenko
2023-02-21 11:49 ` David Woodhouse
2023-02-21 12:14 ` Oleksandr Natalenko
2023-02-21 19:10 ` David Woodhouse
2023-02-21 20:04 ` [External] " Usama Arif
2023-02-21 21:04 ` Oleksandr Natalenko
2023-02-21 21:41 ` Thomas Gleixner
2023-02-21 21:44 ` David Woodhouse
2023-02-21 23:18 ` David Woodhouse
2023-02-22 0:00 ` [External] " Usama Arif
2023-02-22 8:19 ` David Woodhouse
2023-02-22 9:46 ` Thomas Gleixner
2023-02-22 9:51 ` David Woodhouse
2023-02-22 9:31 ` Thomas Gleixner
2023-02-20 22:22 ` Piotr Gorski
2023-02-20 22:23 ` [External] " Usama Arif
2023-02-20 22:41 ` Oleksandr Natalenko
2023-02-22 10:11 ` David Woodhouse
2023-02-22 11:11 ` [External] " Usama Arif
2023-02-22 12:08 ` Brian Gerst
2023-02-22 12:53 ` David Woodhouse
2023-02-22 16:42 ` Thomas Gleixner
2023-02-23 11:07 ` David Woodhouse
2023-02-23 14:37 ` Thomas Gleixner
2023-02-23 15:12 ` David Woodhouse
2023-02-23 19:24 ` [External] " Usama Arif
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