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Message-ID: <CAJZ5v0i4xX75TK=Qg_PUk93aghJgpi0AR0gsa3Repw8G4XyDuw@mail.gmail.com>
Date: Wed, 6 Jul 2022 16:02:52 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: rth@...ddle.net, ink@...assic.park.msu.ru, mattst88@...il.com,
vgupta@...nel.org,
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Subject: Re: [PATCH 20/36] arch/idle: Change arch_cpu_idle() IRQ behaviour
On Wed, Jun 8, 2022 at 4:46 PM Peter Zijlstra <peterz@...radead.org> 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@...radead.org>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
> 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 *)¤t_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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