linux-kernel - Re: [RFC][PATCH 1/4] acpi: Use CPUIDLE_FLAG_TIMER

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Date:   Mon, 21 Sep 2020 20:26:51 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     rjw@...ysocki.net, bp@...en8.de, x86@...nel.org,
        tony.luck@...el.com, lenb@...nel.org, daniel.lezcano@...aro.org,
        linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        linux-pm@...r.kernel.org, ulf.hansson@...aro.org,
        paulmck@...nel.org, tglx@...utronix.de, naresh.kamboju@...aro.org
Subject: Re: [RFC][PATCH 1/4] acpi: Use CPUIDLE_FLAG_TIMER_STOP

On Tue, Sep 15, 2020 at 12:31:58PM +0200, Peter Zijlstra wrote:
> Make acpi_processor_idle use the common broadcast code, there's no
> reason not to. This also removes some RCU usage after
> rcu_idle_enter().
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Acked-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> Reported-by: Borislav Petkov <bp@...e.de>
> Tested-by: Borislav Petkov <bp@...e.de>
> ---
>  drivers/acpi/processor_idle.c |   49 +++++++++++++-----------------------------
>  1 file changed, 16 insertions(+), 33 deletions(-)
> 
> --- a/drivers/acpi/processor_idle.c
> +++ b/drivers/acpi/processor_idle.c
> @@ -161,18 +161,10 @@ static void lapic_timer_propagate_broadc
>  }
>  
>  /* Power(C) State timer broadcast control */
> -static void lapic_timer_state_broadcast(struct acpi_processor *pr,
> -				       struct acpi_processor_cx *cx,
> -				       int broadcast)
> -{
> -	int state = cx - pr->power.states;
> -
> -	if (state >= pr->power.timer_broadcast_on_state) {
> -		if (broadcast)
> -			tick_broadcast_enter();
> -		else
> -			tick_broadcast_exit();
> -	}
> +static bool lapic_timer_needs_broadcast(struct acpi_processor *pr,
> +					struct acpi_processor_cx *cx)
> +{
> +	return cx - pr->power.states >= pr->power.timer_broadcast_on_state;
>  }
>  
>  #else
> @@ -180,9 +172,9 @@ static void lapic_timer_state_broadcast(
>  static void lapic_timer_check_state(int state, struct acpi_processor *pr,
>  				   struct acpi_processor_cx *cstate) { }
>  static void lapic_timer_propagate_broadcast(struct acpi_processor *pr) { }
> -static void lapic_timer_state_broadcast(struct acpi_processor *pr,
> -				       struct acpi_processor_cx *cx,
> -				       int broadcast)
> +
> +static bool lapic_timer_needs_broadcast(struct acpi_processor *pr,
> +					struct acpi_processor_cx *cx)
>  {
>  }

drivers/acpi/processor_idle.c: In function 'lapic_timer_needs_broadcast':
drivers/acpi/processor_idle.c:179:1: warning: no return statement in function returning non-void [-Wreturn-type]

Should this return true or false ?

Guenter

>  
> @@ -568,21 +560,13 @@ static DEFINE_RAW_SPINLOCK(c3_lock);
>   * acpi_idle_enter_bm - enters C3 with proper BM handling
>   * @pr: Target processor
>   * @cx: Target state context
> - * @timer_bc: Whether or not to change timer mode to broadcast
>   */
>  static void acpi_idle_enter_bm(struct acpi_processor *pr,
> -			       struct acpi_processor_cx *cx, bool timer_bc)
> +			       struct acpi_processor_cx *cx)
>  {
>  	acpi_unlazy_tlb(smp_processor_id());
>  
>  	/*
> -	 * Must be done before busmaster disable as we might need to
> -	 * access HPET !
> -	 */
> -	if (timer_bc)
> -		lapic_timer_state_broadcast(pr, cx, 1);
> -
> -	/*
>  	 * disable bus master
>  	 * bm_check implies we need ARB_DIS
>  	 * bm_control implies whether we can do ARB_DIS
> @@ -609,9 +593,6 @@ static void acpi_idle_enter_bm(struct ac
>  		c3_cpu_count--;
>  		raw_spin_unlock(&c3_lock);
>  	}
> -
> -	if (timer_bc)
> -		lapic_timer_state_broadcast(pr, cx, 0);
>  }
>  
>  static int acpi_idle_enter(struct cpuidle_device *dev,
> @@ -630,7 +611,7 @@ static int acpi_idle_enter(struct cpuidl
>  			cx = per_cpu(acpi_cstate[index], dev->cpu);
>  		} else if (cx->type == ACPI_STATE_C3 && pr->flags.bm_check) {
>  			if (cx->bm_sts_skip || !acpi_idle_bm_check()) {
> -				acpi_idle_enter_bm(pr, cx, true);
> +				acpi_idle_enter_bm(pr, cx);
>  				return index;
>  			} else if (drv->safe_state_index >= 0) {
>  				index = drv->safe_state_index;
> @@ -642,15 +623,11 @@ static int acpi_idle_enter(struct cpuidl
>  		}
>  	}
>  
> -	lapic_timer_state_broadcast(pr, cx, 1);
> -
>  	if (cx->type == ACPI_STATE_C3)
>  		ACPI_FLUSH_CPU_CACHE();
>  
>  	acpi_idle_do_entry(cx);
>  
> -	lapic_timer_state_broadcast(pr, cx, 0);
> -
>  	return index;
>  }
>  
> @@ -666,7 +643,7 @@ static int acpi_idle_enter_s2idle(struct
>  			return 0;
>  
>  		if (pr->flags.bm_check) {
> -			acpi_idle_enter_bm(pr, cx, false);
> +			acpi_idle_enter_bm(pr, cx);
>  			return 0;
>  		} else {
>  			ACPI_FLUSH_CPU_CACHE();
> @@ -682,6 +659,7 @@ static int acpi_processor_setup_cpuidle_
>  {
>  	int i, count = ACPI_IDLE_STATE_START;
>  	struct acpi_processor_cx *cx;
> +	struct cpuidle_state *state;
>  
>  	if (max_cstate == 0)
>  		max_cstate = 1;
> @@ -694,6 +672,11 @@ static int acpi_processor_setup_cpuidle_
>  
>  		per_cpu(acpi_cstate[count], dev->cpu) = cx;
>  
> +		if (lapic_timer_needs_broadcast(pr, cx)) {
> +			state = &acpi_idle_driver.states[count];
> +			state->flags |= CPUIDLE_FLAG_TIMER_STOP;
> +		}
> +
>  		count++;
>  		if (count == CPUIDLE_STATE_MAX)
>  			break;