linux-kernel - Re: [PATCH v3 2/3] x86/smp native_play_dead: Prefer cpuidle_play_dead() over mwait_play

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Message-ID: <9152f296-3f81-438d-8dc8-3c0bc60ea4b6@intel.com>
Date: Wed, 13 Nov 2024 17:27:20 +0100
From: "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>
To: Peter Zijlstra <peterz@...radead.org>, "Gautham R. Shenoy"
	<gautham.shenoy@....com>
CC: "Rafael J. Wysocki" <rafael@...nel.org>, Patryk Wlazlyn
	<patryk.wlazlyn@...ux.intel.com>, <x86@...nel.org>,
	<linux-kernel@...r.kernel.org>, <linux-pm@...r.kernel.org>,
	<len.brown@...el.com>, <artem.bityutskiy@...ux.intel.com>,
	<dave.hansen@...ux.intel.com>
Subject: Re: [PATCH v3 2/3] x86/smp native_play_dead: Prefer
 cpuidle_play_dead() over mwait_play_dead()


On 11/13/2024 5:22 PM, Peter Zijlstra wrote:
> On Wed, Nov 13, 2024 at 05:11:38PM +0530, Gautham R. Shenoy wrote:
>
>> How about something like this (completely untested)
>>
>> ---------------------x8----------------------------------------------------
>>
>> diff --git a/arch/x86/kernel/acpi/cstate.c b/arch/x86/kernel/acpi/cstate.c
>> index f3ffd0a3a012..bd611771fa6c 100644
>> --- a/arch/x86/kernel/acpi/cstate.c
>> +++ b/arch/x86/kernel/acpi/cstate.c
>> @@ -215,6 +215,24 @@ void __cpuidle acpi_processor_ffh_cstate_enter(struct acpi_processor_cx *cx)
>>   }
>>   EXPORT_SYMBOL_GPL(acpi_processor_ffh_cstate_enter);
>>   
>> +static int acpi_processor_ffh_play_dead(struct acpi_processor_cx *cx)
>> +{
>> +       unsigned int cpu = smp_processor_id();
>> +       struct cstate_entry *percpu_entry;
>> +
>> +       /*
>> +        * This is ugly. But AMD processors don't prefer MWAIT based
>> +        * C-states when processors are offlined.
>> +        */
>> +       if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
>> +           boot_cpu_data.x86_vendor == X86_VENDOR_HYGON)
>> +               return -ENODEV;
> Are there AMD systems with FFh idle states at all?

I don't know.


> Also, I don't think this works right, the loop in cpuidle_play_dead()
> will terminate on this, and not try a shallower state which might have
> IO/HLT on.

I think you are right.


>> +
>> +       percpu_entry = per_cpu_ptr(cpu_cstate_entry, cpu);
>> +       return mwait_play_dead_with_hints(percpu_entry->states[cx->index].eax);
>> +}
>> +EXPORT_SYMBOL_GPL(acpi_processor_ffh_play_dead);