linux-kernel - Re: [PATCH v1 4/5] ACPI: processor: Rescan "dead" SMT siblings during initialization

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Message-ID: <CAJZ5v0h=d-w3QVdTwC7dApDKE_eVtNxOa1deyG1ru-VTcY_C0g@mail.gmail.com>
Date: Thu, 5 Jun 2025 20:20:37 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Dave Hansen <dave.hansen@...el.com>
Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>, x86 Maintainers <x86@...nel.org>, 
	Linux PM <linux-pm@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, 
	Len Brown <lenb@...nel.org>, Peter Zijlstra <peterz@...radead.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Dave Hansen <dave.hansen@...ux.intel.com>, 
	Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>, 
	"Gautham R. Shenoy" <gautham.shenoy@....com>, Ingo Molnar <mingo@...hat.com>, 
	Borislav Petkov <bp@...en8.de>, Linux ACPI <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH v1 4/5] ACPI: processor: Rescan "dead" SMT siblings during initialization

On Thu, Jun 5, 2025 at 6:14 PM Dave Hansen <dave.hansen@...el.com> wrote:
>
> On 6/5/25 08:07, Rafael J. Wysocki wrote:
> >  #ifdef CONFIG_ACPI_PROCESSOR_CSTATE
> > +void acpi_idle_rescan_dead_smt_siblings(void)
> > +{
> > +     if (cpuidle_get_driver() == &acpi_idle_driver)
> > +             arch_cpu_rescan_dead_smt_siblings();
> > +}
>
> My only thought in reading this is that maybe cpuidle_register_driver()
> would be a better spot to force the arch_cpu_rescan_dead_smt_siblings().
> That way, each driver would not have to do the rescan.

Unfortunately, this wouldn't work in the current arrangement of things
because cpuidle_register_driver() can be called in a CPU online path.

It should be possible to make this work in the future, but first things first.

> But that's just a little nit at worst, otherwise the series looks good
> to me. Thanks for chasing this down.
>
> For the x86 bits:
>
> Acked-by: Dave Hansen <dave.hansen@...ux.intel.com>

Thank you!