Re: [Xen-devel] [PATCH 1/3] mwait-idle: add support for using halt

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, Feb 25, 2019 at 08:23:58PM +0000, Woods, Brian wrote:
> Some AMD processors can use a mixture of mwait and halt for accessing
> various c-states.  In preparation for adding support for AMD processors,
> update the mwait-idle driver to optionally use halt.
> 
> Signed-off-by: Brian Woods <brian.woods@xxxxxxx>
> ---
>  xen/arch/x86/cpu/mwait-idle.c | 40 +++++++++++++++++++++++++++++++++-------
>  1 file changed, 33 insertions(+), 7 deletions(-)
> 
> diff --git a/xen/arch/x86/cpu/mwait-idle.c b/xen/arch/x86/cpu/mwait-idle.c
> index f89c52f256..a063e39d60 100644
> --- a/xen/arch/x86/cpu/mwait-idle.c
> +++ b/xen/arch/x86/cpu/mwait-idle.c
> @@ -103,6 +103,11 @@ static const struct cpuidle_state {
>  
>  #define CPUIDLE_FLAG_DISABLED                0x1
>  /*
> + * On certain AMD families that support mwait, only c1 can be reached by
> + * mwait and to reach c2, halt has to be used.
> + */
> +#define CPUIDLE_FLAG_USE_HALT                0x2
> +/*
>   * Set this flag for states where the HW flushes the TLB for us
>   * and so we don't need cross-calls to keep it consistent.
>   * If this flag is set, SW flushes the TLB, so even if the
> @@ -783,8 +788,23 @@ static void mwait_idle(void)
>  
>       update_last_cx_stat(power, cx, before);
>  
> -     if (cpu_is_haltable(cpu))
> -             mwait_idle_with_hints(eax, MWAIT_ECX_INTERRUPT_BREAK);
> +     if (cpu_is_haltable(cpu)) {
> +             struct cpu_info *info;
> +             switch (cx->entry_method) {
> +             case ACPI_CSTATE_EM_FFH:
> +                     mwait_idle_with_hints(eax, MWAIT_ECX_INTERRUPT_BREAK);
> +                     break;
> +             case ACPI_CSTATE_EM_HALT:

> +                     info = get_cpu_info();
> +                     spec_ctrl_enter_idle(info);
> +                     safe_halt();
> +                     spec_ctrl_exit_idle(info);

May I suggest you make this snippet a function? The same code snippet
appears a few lines above.

Wei.

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel