linux-kernel - Re: [patch 06/26] metag: Use irq_set_affinity instead of homebrewn code

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Message-ID: <530B47FD.80608@imgtec.com>
Date:	Mon, 24 Feb 2014 13:24:13 +0000
From:	James Hogan <james.hogan@...tec.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	"Peter Zijlstra" <peterz@...radead.org>,
	metag <linux-metag@...r.kernel.org>
Subject: Re: [patch 06/26] metag: Use irq_set_affinity instead of homebrewn
 code

Hi Thomas,

On 23/02/14 21:40, Thomas Gleixner wrote:
> There is no point in having an incomplete copy of irq_set_affinity()
> for the hotplug irq migration code.

That sounds reasonable, but when I gave it a try I started getting
warnings on the log after offlining one cpu then the other:

META213-Thread0 DSP [LogF] IRQ13 no longer affine to CPU1
META213-Thread0 DSP [LogF] IRQ14 no longer affine to CPU1
META213-Thread0 DSP [LogF] IRQ15 no longer affine to CPU1
META213-Thread0 DSP [LogF] IRQ18 no longer affine to CPU1
META213-Thread0 DSP [LogF] IRQ29 no longer affine to CPU1
META213-Thread0 DSP [LogF] IRQ30 no longer affine to CPU1
META213-Thread0 DSP [LogF] IRQ31 no longer affine to CPU1

It appears that the irq affinities weren't getting modified previously,
whereas now irq_do_set_affinity() does do cpumask_copy(data->affinity,
mask). Once all CPUs have been offlined at least once you get those
spurious messages even though the IRQ affinities haven't been explicitly
limited by anything.

I wonder if the stored affinity should really be altered in this case?

Cheers
James

> 
> Use the core function instead and while at it switch to
> for_each_active_irq()
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Cc: James Hogan <james.hogan@...tec.com>
> Cc: metag <linux-metag@...r.kernel.org>
> ---
>  arch/metag/kernel/irq.c |   20 +++-----------------
>  1 file changed, 3 insertions(+), 17 deletions(-)
> 
> Index: tip/arch/metag/kernel/irq.c
> ===================================================================
> --- tip.orig/arch/metag/kernel/irq.c
> +++ tip/arch/metag/kernel/irq.c
> @@ -261,18 +261,6 @@ int __init arch_probe_nr_irqs(void)
>  }
>  
>  #ifdef CONFIG_HOTPLUG_CPU
> -static void route_irq(struct irq_data *data, unsigned int irq, unsigned int cpu)
> -{
> -	struct irq_desc *desc = irq_to_desc(irq);
> -	struct irq_chip *chip = irq_data_get_irq_chip(data);
> -	unsigned long flags;
> -
> -	raw_spin_lock_irqsave(&desc->lock, flags);
> -	if (chip->irq_set_affinity)
> -		chip->irq_set_affinity(data, cpumask_of(cpu), false);
> -	raw_spin_unlock_irqrestore(&desc->lock, flags);
> -}
> -
>  /*
>   * The CPU has been marked offline.  Migrate IRQs off this CPU.  If
>   * the affinity settings do not allow other CPUs, force them onto any
> @@ -281,10 +269,9 @@ static void route_irq(struct irq_data *d
>  void migrate_irqs(void)
>  {
>  	unsigned int i, cpu = smp_processor_id();
> -	struct irq_desc *desc;
>  
> -	for_each_irq_desc(i, desc) {
> -		struct irq_data *data = irq_desc_get_irq_data(desc);
> +	for_each_active_irq(i) {
> +		struct irq_data *data = irq_get_irq_data(i);
>  		unsigned int newcpu;
>  
>  		if (irqd_is_per_cpu(data))
> @@ -303,8 +290,7 @@ void migrate_irqs(void)
>  			newcpu = cpumask_any_and(data->affinity,
>  						 cpu_online_mask);
>  		}
> -
> -		route_irq(data, i, newcpu);
> +		irq_set_affinity(i, cpumask_of(newcpu));
>  	}
>  }
>  #endif /* CONFIG_HOTPLUG_CPU */
> 
> 


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