Re: [PATCH v2] x86/acpi/cstate: Optimize ARB_DISABLE on Centaur CPUs

[Rafael J. Wysocki]

On Mon, Nov 7, 2022 at 4:35 AM Tony W Wang-oc <TonyWWang-oc@xxxxxxxxxxx> wrote:
>
> On all recent Centaur platforms, ARB_DISABLE is handled by PMU
> automatically while entering C3 type state. No need for OS to
> issue the ARB_DISABLE, so set bm_control to zero to indicate that.
>
> Signed-off-by: Tony W Wang-oc <TonyWWang-oc@xxxxxxxxxxx>

Acked-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>

Or x86 maintainers please let me know if you want me to take care of this.

Thanks!

> ---
> Changes in V2:
>  - fix typo in comments.
> ---
>  arch/x86/kernel/acpi/cstate.c | 26 +++++++++++++++++---------
>  1 file changed, 17 insertions(+), 9 deletions(-)
>
> diff --git a/arch/x86/kernel/acpi/cstate.c b/arch/x86/kernel/acpi/cstate.c
> index 7945eae..da71679 100644
> --- a/arch/x86/kernel/acpi/cstate.c
> +++ b/arch/x86/kernel/acpi/cstate.c
> @@ -52,17 +52,25 @@ void acpi_processor_power_init_bm_check(struct acpi_processor_flags *flags,
>         if (c->x86_vendor == X86_VENDOR_INTEL &&
>             (c->x86 > 0xf || (c->x86 == 6 && c->x86_model >= 0x0f)))
>                         flags->bm_control = 0;
> -       /*
> -        * For all recent Centaur CPUs, the ucode will make sure that each
> -        * core can keep cache coherence with each other while entering C3
> -        * type state. So, set bm_check to 1 to indicate that the kernel
> -        * doesn't need to execute a cache flush operation (WBINVD) when
> -        * entering C3 type state.
> -        */
> +
>         if (c->x86_vendor == X86_VENDOR_CENTAUR) {
>                 if (c->x86 > 6 || (c->x86 == 6 && c->x86_model == 0x0f &&
> -                   c->x86_stepping >= 0x0e))
> -                       flags->bm_check = 1;
> +                   c->x86_stepping >= 0x0e)) {
> +                       /*
> +                        * For all recent Centaur CPUs, the ucode will make sure that each
> +                        * core can keep cache coherence with each other while entering C3
> +                        * type state. So, set bm_check to 1 to indicate that the kernel
> +                        * doesn't need to execute a cache flush operation (WBINVD) when
> +                        * entering C3 type state.
> +                        */
> +                       flags->bm_check = 1;
> +                       /*
> +                        * For all recent Centaur platforms, ARB_DISABLE is a nop.
> +                        * Set bm_control to zero to indicate that ARB_DISABLE is
> +                        * not required while entering C3 type state.
> +                        */
> +                       flags->bm_control = 0;
> +               }
>         }
>
>         if (c->x86_vendor == X86_VENDOR_ZHAOXIN) {
> --
> 2.7.4
>