From: David Woodhouse <dwmw2@infradead.org>
To: Usama Arif <usama.arif@bytedance.com>,
Thomas Gleixner <tglx@linutronix.de>,
Oleksandr Natalenko <oleksandr@natalenko.name>
Cc: Kim Phillips <kim.phillips@amd.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: [External] Re: [PATCH v9 0/8] Parallel CPU bringup for x86_64
Date: Wed, 22 Feb 2023 08:19:27 +0000 [thread overview]
Message-ID: <e7036423216287e86eab4daf9dd1acdaecdd2b49.camel@infradead.org> (raw)
In-Reply-To: <11cc090b-82aa-f2f5-0f08-b8e63e662947@bytedance.com>
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On Wed, 2023-02-22 at 00:00 +0000, Usama Arif wrote:
>
> > diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
> > index 33c0d5fd8af6..72b9375fec7c 100644
> > --- a/arch/x86/include/asm/smp.h
> > +++ b/arch/x86/include/asm/smp.h
> > @@ -208,4 +208,6 @@ extern unsigned int smpboot_control;
> > #define STARTUP_APICID_CPUID_0B 0x40000000
> > #define STARTUP_APICID_CPUID_01 0x20000000
> >
> > +#define STARTUP_PARALLEL_MASK 0x60000000
> > +
>
> Probably could define STARTUP_PARALLEL_MASK as STARTUP_APICID_CPUID_0B |
> STARTUP_APICID_CPUID_01 instead? otherwise if its a separate bit, it
> needs to be set in native_smp_prepare_cpus as well for this to work?
It is CPUID_0B | CPUID_01, unless I was being really stupid last night.
Sips coffee... yep, 6 = 4 | 2. I could have made that more obvious with
a bit more typing, I suppose.
However, I don't think this approach is correct. The idle thread stacks
for the other CPUs are *unused* because those CPUs are offline. So we
can use them with impunity, and when those CPUs come back online
they'll call into cpu_startup_entry(CPUHP_AP_ONLINE_IDLE) using the
correct stack.
But the BSP/CPU0 is different. It hasn't actually been taken offline,
and its idle thread context is still in cpu_startup_entry(CPUHP_ONLINE)
which got called from rest_init().
In testing I probably got away with it because we're only using the
*top* of the stack, don't use anything of the red zone, and thus don't
actually bother the true idle thread which is never going to return.
But I don't think it's correct; we really ought to have that temp_stack
unless we're going to refactor the wakeup_64 code to *become* the idle
thread just as startup_secondary() does, and *schedule* to the context
that was saved in the suspend code.
That might be an interesting cleanup, and let us use the normal
__switch_to() to save and restore a bunch of context which is currently
done by hand.
But not today.
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next prev parent reply other threads:[~2023-02-22 8:20 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
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 [this message]
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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