Re: [PATCH 20/36] arch/idle: Change arch_cpu_idle() IRQ behaviour

[Mark Rutland <mark.rutland@arm.com>]

On Wed, Jun 08, 2022 at 04:27:43PM +0200, Peter Zijlstra wrote:
> Current arch_cpu_idle() is called with IRQs disabled, but will return
> with IRQs enabled.
> 
> However, the very first thing the generic code does after calling
> arch_cpu_idle() is raw_local_irq_disable(). This means that
> architectures that can idle with IRQs disabled end up doing a
> pointless 'enable-disable' dance.
> 
> Therefore, push this IRQ disabling into the idle function, meaning
> that those architectures can avoid the pointless IRQ state flipping.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Nice!

  Acked-by: Mark Rutland <mark.rutland@arm.com> [arm64]

Mark.

> ---
>  arch/alpha/kernel/process.c      |    1 -
>  arch/arc/kernel/process.c        |    3 +++
>  arch/arm/kernel/process.c        |    1 -
>  arch/arm/mach-gemini/board-dt.c  |    3 ++-
>  arch/arm64/kernel/idle.c         |    1 -
>  arch/csky/kernel/process.c       |    1 -
>  arch/csky/kernel/smp.c           |    2 +-
>  arch/hexagon/kernel/process.c    |    1 -
>  arch/ia64/kernel/process.c       |    1 +
>  arch/microblaze/kernel/process.c |    1 -
>  arch/mips/kernel/idle.c          |    8 +++-----
>  arch/nios2/kernel/process.c      |    1 -
>  arch/openrisc/kernel/process.c   |    1 +
>  arch/parisc/kernel/process.c     |    2 --
>  arch/powerpc/kernel/idle.c       |    5 ++---
>  arch/riscv/kernel/process.c      |    1 -
>  arch/s390/kernel/idle.c          |    1 -
>  arch/sh/kernel/idle.c            |    1 +
>  arch/sparc/kernel/leon_pmc.c     |    4 ++++
>  arch/sparc/kernel/process_32.c   |    1 -
>  arch/sparc/kernel/process_64.c   |    3 ++-
>  arch/um/kernel/process.c         |    1 -
>  arch/x86/coco/tdx/tdx.c          |    3 +++
>  arch/x86/kernel/process.c        |   15 ++++-----------
>  arch/xtensa/kernel/process.c     |    1 +
>  kernel/sched/idle.c              |    2 --
>  26 files changed, 28 insertions(+), 37 deletions(-)
> 
> --- a/arch/alpha/kernel/process.c
> +++ b/arch/alpha/kernel/process.c
> @@ -57,7 +57,6 @@ EXPORT_SYMBOL(pm_power_off);
>  void arch_cpu_idle(void)
>  {
>  	wtint(0);
> -	raw_local_irq_enable();
>  }
>  
>  void arch_cpu_idle_dead(void)
> --- a/arch/arc/kernel/process.c
> +++ b/arch/arc/kernel/process.c
> @@ -114,6 +114,8 @@ void arch_cpu_idle(void)
>  		"sleep %0	\n"
>  		:
>  		:"I"(arg)); /* can't be "r" has to be embedded const */
> +
> +	raw_local_irq_disable();
>  }
>  
>  #else	/* ARC700 */
> @@ -122,6 +124,7 @@ void arch_cpu_idle(void)
>  {
>  	/* sleep, but enable both set E1/E2 (levels of interrupts) before committing */
>  	__asm__ __volatile__("sleep 0x3	\n");
> +	raw_local_irq_disable();
>  }
>  
>  #endif
> --- a/arch/arm/kernel/process.c
> +++ b/arch/arm/kernel/process.c
> @@ -78,7 +78,6 @@ void arch_cpu_idle(void)
>  		arm_pm_idle();
>  	else
>  		cpu_do_idle();
> -	raw_local_irq_enable();
>  }
>  
>  void arch_cpu_idle_prepare(void)
> --- a/arch/arm/mach-gemini/board-dt.c
> +++ b/arch/arm/mach-gemini/board-dt.c
> @@ -42,8 +42,9 @@ static void gemini_idle(void)
>  	 */
>  
>  	/* FIXME: Enabling interrupts here is racy! */
> -	local_irq_enable();
> +	raw_local_irq_enable();
>  	cpu_do_idle();
> +	raw_local_irq_disable();
>  }
>  
>  static void __init gemini_init_machine(void)
> --- a/arch/arm64/kernel/idle.c
> +++ b/arch/arm64/kernel/idle.c
> @@ -42,5 +42,4 @@ void noinstr arch_cpu_idle(void)
>  	 * tricks
>  	 */
>  	cpu_do_idle();
> -	raw_local_irq_enable();
>  }
> --- a/arch/csky/kernel/process.c
> +++ b/arch/csky/kernel/process.c
> @@ -101,6 +101,5 @@ void arch_cpu_idle(void)
>  #ifdef CONFIG_CPU_PM_STOP
>  	asm volatile("stop\n");
>  #endif
> -	raw_local_irq_enable();
>  }
>  #endif
> --- a/arch/csky/kernel/smp.c
> +++ b/arch/csky/kernel/smp.c
> @@ -314,7 +314,7 @@ void arch_cpu_idle_dead(void)
>  	while (!secondary_stack)
>  		arch_cpu_idle();
>  
> -	local_irq_disable();
> +	raw_local_irq_disable();
>  
>  	asm volatile(
>  		"mov	sp, %0\n"
> --- a/arch/hexagon/kernel/process.c
> +++ b/arch/hexagon/kernel/process.c
> @@ -44,7 +44,6 @@ void arch_cpu_idle(void)
>  {
>  	__vmwait();
>  	/*  interrupts wake us up, but irqs are still disabled */
> -	raw_local_irq_enable();
>  }
>  
>  /*
> --- a/arch/ia64/kernel/process.c
> +++ b/arch/ia64/kernel/process.c
> @@ -241,6 +241,7 @@ void arch_cpu_idle(void)
>  		(*mark_idle)(1);
>  
>  	raw_safe_halt();
> +	raw_local_irq_disable();
>  
>  	if (mark_idle)
>  		(*mark_idle)(0);
> --- a/arch/microblaze/kernel/process.c
> +++ b/arch/microblaze/kernel/process.c
> @@ -138,5 +138,4 @@ int dump_fpu(struct pt_regs *regs, elf_f
>  
>  void arch_cpu_idle(void)
>  {
> -       raw_local_irq_enable();
>  }
> --- a/arch/mips/kernel/idle.c
> +++ b/arch/mips/kernel/idle.c
> @@ -33,13 +33,13 @@ static void __cpuidle r3081_wait(void)
>  {
>  	unsigned long cfg = read_c0_conf();
>  	write_c0_conf(cfg | R30XX_CONF_HALT);
> -	raw_local_irq_enable();
>  }
>  
>  void __cpuidle r4k_wait(void)
>  {
>  	raw_local_irq_enable();
>  	__r4k_wait();
> +	raw_local_irq_disable();
>  }
>  
>  /*
> @@ -57,7 +57,6 @@ void __cpuidle r4k_wait_irqoff(void)
>  		"	.set	arch=r4000	\n"
>  		"	wait			\n"
>  		"	.set	pop		\n");
> -	raw_local_irq_enable();
>  }
>  
>  /*
> @@ -77,7 +76,6 @@ static void __cpuidle rm7k_wait_irqoff(v
>  		"	wait						\n"
>  		"	mtc0	$1, $12		# stalls until W stage	\n"
>  		"	.set	pop					\n");
> -	raw_local_irq_enable();
>  }
>  
>  /*
> @@ -103,6 +101,8 @@ static void __cpuidle au1k_wait(void)
>  	"	nop				\n"
>  	"	.set	pop			\n"
>  	: : "r" (au1k_wait), "r" (c0status));
> +
> +	raw_local_irq_disable();
>  }
>  
>  static int __initdata nowait;
> @@ -245,8 +245,6 @@ void arch_cpu_idle(void)
>  {
>  	if (cpu_wait)
>  		cpu_wait();
> -	else
> -		raw_local_irq_enable();
>  }
>  
>  #ifdef CONFIG_CPU_IDLE
> --- a/arch/nios2/kernel/process.c
> +++ b/arch/nios2/kernel/process.c
> @@ -33,7 +33,6 @@ EXPORT_SYMBOL(pm_power_off);
>  
>  void arch_cpu_idle(void)
>  {
> -	raw_local_irq_enable();
>  }
>  
>  /*
> --- a/arch/openrisc/kernel/process.c
> +++ b/arch/openrisc/kernel/process.c
> @@ -102,6 +102,7 @@ void arch_cpu_idle(void)
>  	raw_local_irq_enable();
>  	if (mfspr(SPR_UPR) & SPR_UPR_PMP)
>  		mtspr(SPR_PMR, mfspr(SPR_PMR) | SPR_PMR_DME);
> +	raw_local_irq_disable();
>  }
>  
>  void (*pm_power_off)(void) = NULL;
> --- a/arch/parisc/kernel/process.c
> +++ b/arch/parisc/kernel/process.c
> @@ -187,8 +187,6 @@ void arch_cpu_idle_dead(void)
>  
>  void __cpuidle arch_cpu_idle(void)
>  {
> -	raw_local_irq_enable();
> -
>  	/* nop on real hardware, qemu will idle sleep. */
>  	asm volatile("or %%r10,%%r10,%%r10\n":::);
>  }
> --- a/arch/powerpc/kernel/idle.c
> +++ b/arch/powerpc/kernel/idle.c
> @@ -51,10 +51,9 @@ void arch_cpu_idle(void)
>  		 * Some power_save functions return with
>  		 * interrupts enabled, some don't.
>  		 */
> -		if (irqs_disabled())
> -			raw_local_irq_enable();
> +		if (!irqs_disabled())
> +			raw_local_irq_disable();
>  	} else {
> -		raw_local_irq_enable();
>  		/*
>  		 * Go into low thread priority and possibly
>  		 * low power mode.
> --- a/arch/riscv/kernel/process.c
> +++ b/arch/riscv/kernel/process.c
> @@ -39,7 +39,6 @@ extern asmlinkage void ret_from_kernel_t
>  void arch_cpu_idle(void)
>  {
>  	cpu_do_idle();
> -	raw_local_irq_enable();
>  }
>  
>  void __show_regs(struct pt_regs *regs)
> --- a/arch/s390/kernel/idle.c
> +++ b/arch/s390/kernel/idle.c
> @@ -66,7 +66,6 @@ void arch_cpu_idle(void)
>  	idle->idle_count++;
>  	account_idle_time(cputime_to_nsecs(idle_time));
>  	raw_write_seqcount_end(&idle->seqcount);
> -	raw_local_irq_enable();
>  }
>  
>  static ssize_t show_idle_count(struct device *dev,
> --- a/arch/sh/kernel/idle.c
> +++ b/arch/sh/kernel/idle.c
> @@ -25,6 +25,7 @@ void default_idle(void)
>  	raw_local_irq_enable();
>  	/* Isn't this racy ? */
>  	cpu_sleep();
> +	raw_local_irq_disable();
>  	clear_bl_bit();
>  }
>  
> --- a/arch/sparc/kernel/leon_pmc.c
> +++ b/arch/sparc/kernel/leon_pmc.c
> @@ -57,6 +57,8 @@ static void pmc_leon_idle_fixup(void)
>  		"lda	[%0] %1, %%g0\n"
>  		:
>  		: "r"(address), "i"(ASI_LEON_BYPASS));
> +
> +	raw_local_irq_disable();
>  }
>  
>  /*
> @@ -70,6 +72,8 @@ static void pmc_leon_idle(void)
>  
>  	/* For systems without power-down, this will be no-op */
>  	__asm__ __volatile__ ("wr	%g0, %asr19\n\t");
> +
> +	raw_local_irq_disable();
>  }
>  
>  /* Install LEON Power Down function */
> --- a/arch/sparc/kernel/process_32.c
> +++ b/arch/sparc/kernel/process_32.c
> @@ -71,7 +71,6 @@ void arch_cpu_idle(void)
>  {
>  	if (sparc_idle)
>  		(*sparc_idle)();
> -	raw_local_irq_enable();
>  }
>  
>  /* XXX cli/sti -> local_irq_xxx here, check this works once SMP is fixed. */
> --- a/arch/sparc/kernel/process_64.c
> +++ b/arch/sparc/kernel/process_64.c
> @@ -59,7 +59,6 @@ void arch_cpu_idle(void)
>  {
>  	if (tlb_type != hypervisor) {
>  		touch_nmi_watchdog();
> -		raw_local_irq_enable();
>  	} else {
>  		unsigned long pstate;
>  
> @@ -90,6 +89,8 @@ void arch_cpu_idle(void)
>  			"wrpr %0, %%g0, %%pstate"
>  			: "=&r" (pstate)
>  			: "i" (PSTATE_IE));
> +
> +		raw_local_irq_disable();
>  	}
>  }
>  
> --- a/arch/um/kernel/process.c
> +++ b/arch/um/kernel/process.c
> @@ -216,7 +216,6 @@ void arch_cpu_idle(void)
>  {
>  	cpu_tasks[current_thread_info()->cpu].pid = os_getpid();
>  	um_idle_sleep();
> -	raw_local_irq_enable();
>  }
>  
>  int __cant_sleep(void) {
> --- a/arch/x86/coco/tdx/tdx.c
> +++ b/arch/x86/coco/tdx/tdx.c
> @@ -178,6 +178,9 @@ void __cpuidle tdx_safe_halt(void)
>  	 */
>  	if (__halt(irq_disabled, do_sti))
>  		WARN_ONCE(1, "HLT instruction emulation failed\n");
> +
> +	/* XXX I can't make sense of what @do_sti actually does */
> +	raw_local_irq_disable();
>  }
>  
>  static bool read_msr(struct pt_regs *regs)
> --- a/arch/x86/kernel/process.c
> +++ b/arch/x86/kernel/process.c
> @@ -699,6 +699,7 @@ EXPORT_SYMBOL(boot_option_idle_override)
>  void __cpuidle default_idle(void)
>  {
>  	raw_safe_halt();
> +	raw_local_irq_disable();
>  }
>  #if defined(CONFIG_APM_MODULE) || defined(CONFIG_HALTPOLL_CPUIDLE_MODULE)
>  EXPORT_SYMBOL(default_idle);
> @@ -804,13 +805,7 @@ static void amd_e400_idle(void)
>  
>  	default_idle();
>  
> -	/*
> -	 * The switch back from broadcast mode needs to be called with
> -	 * interrupts disabled.
> -	 */
> -	raw_local_irq_disable();
>  	tick_broadcast_exit();
> -	raw_local_irq_enable();
>  }
>  
>  /*
> @@ -849,12 +844,10 @@ static __cpuidle void mwait_idle(void)
>  		}
>  
>  		__monitor((void *)&current_thread_info()->flags, 0, 0);
> -		if (!need_resched())
> +		if (!need_resched()) {
>  			__sti_mwait(0, 0);
> -		else
> -			raw_local_irq_enable();
> -	} else {
> -		raw_local_irq_enable();
> +			raw_local_irq_disable();
> +		}
>  	}
>  	__current_clr_polling();
>  }
> --- a/arch/xtensa/kernel/process.c
> +++ b/arch/xtensa/kernel/process.c
> @@ -183,6 +183,7 @@ void coprocessor_flush_release_all(struc
>  void arch_cpu_idle(void)
>  {
>  	platform_idle();
> +	raw_local_irq_disable();
>  }
>  
>  /*
> --- a/kernel/sched/idle.c
> +++ b/kernel/sched/idle.c
> @@ -79,7 +79,6 @@ void __weak arch_cpu_idle_dead(void) { }
>  void __weak arch_cpu_idle(void)
>  {
>  	cpu_idle_force_poll = 1;
> -	raw_local_irq_enable();
>  }
>  
>  /**
> @@ -96,7 +95,6 @@ void __cpuidle default_idle_call(void)
>  
>  		cpuidle_rcu_enter();
>  		arch_cpu_idle();
> -		raw_local_irq_disable();
>  		cpuidle_rcu_exit();
>  
>  		start_critical_timings();
> 
> 

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