Re: [PATCH v3 2/3] x86/smp native_play_dead: Prefer cpuidle_play_dead() over mwait_play_dead()
From: Peter Zijlstra
Date: Wed Nov 13 2024 - 11:46:16 EST
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?
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.
> +
> + 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);