Re: [PATCH 02/36] x86/idle: Replace x86_idle with a static_call

Rafael J. Wysocki
2022-06-08T18:15:38Z

On Wed, Jun 8, 2022 at 4:47 PM Peter Zijlstra <peterz@infradead.org> wrote:
>
> Typical boot time setup; no need to suffer an indirect call for that.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Reviewed-by: Frederic Weisbecker <frederic@kernel.org>

Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

> ---
> arch/x86/kernel/process.c | 50 +++++++++++++++++++++++++---------------------
> 1 file changed, 28 insertions(+), 22 deletions(-)
>
> --- a/arch/x86/kernel/process.c
> +++ b/arch/x86/kernel/process.c
> @@ -24,6 +24,7 @@
> #include <linux/cpuidle.h>
> #include <linux/acpi.h>
> #include <linux/elf-randomize.h>
> +#include <linux/static_call.h>
> #include <trace/events/power.h>
> #include <linux/hw_breakpoint.h>
> #include <asm/cpu.h>
> @@ -692,7 +693,23 @@ void __switch_to_xtra(struct task_struct
> unsigned long boot_option_idle_override = IDLE_NO_OVERRIDE;
> EXPORT_SYMBOL(boot_option_idle_override);
>
> -static void (*x86_idle)(void);
> +/*
> + * We use this if we don't have any better idle routine..
> + */
> +void __cpuidle default_idle(void)
> +{
> + raw_safe_halt();
> +}
> +#if defined(CONFIG_APM_MODULE) || defined(CONFIG_HALTPOLL_CPUIDLE_MODULE)
> +EXPORT_SYMBOL(default_idle);
> +#endif
> +
> +DEFINE_STATIC_CALL_NULL(x86_idle, default_idle);
> +
> +static bool x86_idle_set(void)
> +{
> + return !!static_call_query(x86_idle);
> +}
>
> #ifndef CONFIG_SMP
> static inline void play_dead(void)
> @@ -715,28 +732,17 @@ void arch_cpu_idle_dead(void)
> /*
> * Called from the generic idle code.
> */
> -void arch_cpu_idle(void)
> -{
> - x86_idle();
> -}
> -
> -/*
> - * We use this if we don't have any better idle routine..
> - */
> -void __cpuidle default_idle(void)
> +void __cpuidle arch_cpu_idle(void)
> {
> - raw_safe_halt();
> + static_call(x86_idle)();
> }
> -#if defined(CONFIG_APM_MODULE) || defined(CONFIG_HALTPOLL_CPUIDLE_MODULE)
> -EXPORT_SYMBOL(default_idle);
> -#endif
>
> #ifdef CONFIG_XEN
> bool xen_set_default_idle(void)
> {
> - bool ret = !!x86_idle;
> + bool ret = x86_idle_set();
>
> - x86_idle = default_idle;
> + static_call_update(x86_idle, default_idle);
>
> return ret;
> }
> @@ -859,20 +865,20 @@ void select_idle_routine(const struct cp
> if (boot_option_idle_override == IDLE_POLL && smp_num_siblings > 1)
> pr_warn_once("WARNING: polling idle and HT enabled, performance may degrade\n");
> #endif
> - if (x86_idle || boot_option_idle_override == IDLE_POLL)
> + if (x86_idle_set() || boot_option_idle_override == IDLE_POLL)
> return;
>
> if (boot_cpu_has_bug(X86_BUG_AMD_E400)) {
> pr_info("using AMD E400 aware idle routine\n");
> - x86_idle = amd_e400_idle;
> + static_call_update(x86_idle, amd_e400_idle);
> } else if (prefer_mwait_c1_over_halt(c)) {
> pr_info("using mwait in idle threads\n");
> - x86_idle = mwait_idle;
> + static_call_update(x86_idle, mwait_idle);
> } else if (cpu_feature_enabled(X86_FEATURE_TDX_GUEST)) {
> pr_info("using TDX aware idle routine\n");
> - x86_idle = tdx_safe_halt;
> + static_call_update(x86_idle, tdx_safe_halt);
> } else
> - x86_idle = default_idle;
> + static_call_update(x86_idle, default_idle);
> }
>
> void amd_e400_c1e_apic_setup(void)
> @@ -925,7 +931,7 @@ static int __init idle_setup(char *str)
> * To continue to load the CPU idle driver, don't touch
> * the boot_option_idle_override.
> */
> - x86_idle = default_idle;
> + static_call_update(x86_idle, default_idle);
> boot_option_idle_override = IDLE_HALT;
> } else if (!strcmp(str, "nomwait")) {
> /*
>
>