linux-kernel - Re: [PATCH v2 5/5] ARC: MCIP: Use IDU_M_DISTRI_DEST mode if there is only 1 destination core

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Date:   Tue, 25 Oct 2016 10:52:42 -0700
From:   Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:     Yuriy Kolerov <yuriy.kolerov@...opsys.com>,
        <linux-snps-arc@...ts.infradead.org>
CC:     <marc.zyngier@....com>, <Vineet.Gupta1@...opsys.com>,
        <Alexey.Brodkin@...opsys.com>, <linux-kernel@...r.kernel.org>,
        <tglx@...utronix.de>
Subject: Re: [PATCH v2 5/5] ARC: MCIP: Use IDU_M_DISTRI_DEST mode if there is
 only 1 destination core

On 10/24/2016 05:46 AM, Yuriy Kolerov wrote:
> ARC linux uses 2 distribution modes for common interrupts: round robin
> mode (IDU_M_DISTRI_RR) and a simple destination mode (IDU_M_DISTRI_DEST).
> The first one is used when more than 1 cores may handle a common interrupt
> and the second one is used when only 1 core may handle a common interrupt.
> 
> However idu_irq_set_affinity always sets IDU_M_DISTRI_RR for all affinity
> values. But there is no sense in setting of such mode if only 1 core must
> handle a common interrupt.
> 
> Signed-off-by: Yuriy Kolerov <yuriy.kolerov@...opsys.com>
> ---
>  arch/arc/kernel/mcip.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arc/kernel/mcip.c b/arch/arc/kernel/mcip.c
> index 090f0a1..75e6d73 100644
> --- a/arch/arc/kernel/mcip.c
> +++ b/arch/arc/kernel/mcip.c
> @@ -197,6 +197,7 @@ idu_irq_set_affinity(struct irq_data *data, const struct cpumask *cpumask,
>  {
>  	unsigned long flags;
>  	cpumask_t online;
> +	unsigned long dest_bits;
>  
>  	/* errout if no online cpu per @cpumask */
>  	if (!cpumask_and(&online, cpumask, cpu_online_mask))
> @@ -204,8 +205,14 @@ idu_irq_set_affinity(struct irq_data *data, const struct cpumask *cpumask,
>  
>  	raw_spin_lock_irqsave(&mcip_lock, flags);
>  
> -	idu_set_dest(data->hwirq, cpumask_bits(&online)[0]);
> -	idu_set_mode(data->hwirq, IDU_M_TRIG_LEVEL, IDU_M_DISTRI_RR);
> +	dest_bits = cpumask_bits(&online)[0];
> +	idu_set_dest(data->hwirq, dest_bits);
> +
> +	if (ffs(dest_bits) == fls(dest_bits)) {
> +		idu_set_mode(data->hwirq, IDU_M_TRIG_LEVEL, IDU_M_DISTRI_DEST);
> +	} else {
> +		idu_set_mode(data->hwirq, IDU_M_TRIG_LEVEL, IDU_M_DISTRI_RR);
> +	}

Better to use a local variable to assign IDU_M_xxx and then call idu_set_mode()
outside the if. I know the compiler would do that anyways, but that looks simpler
to read !

But on the other hand, adding all of this here - isn't there some sort of
duplication of code now between here and in the idu_irq_xlate() ?
Do we need the same stuff in 2 places ?

>  
>  	raw_spin_unlock_irqrestore(&mcip_lock, flags);
>  
>