linux-kernel - Re: [PATCH 2/2] arm64: take onlined cpus into account when setting irq affinity in migrate_one

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Date:	Wed, 27 Aug 2014 11:40:00 +0100
From:	Sudeep Holla <sudeep.holla@....com>
To:	"byungchul.park@....com" <byungchul.park@....com>,
	Will Deacon <Will.Deacon@....com>
CC:	Sudeep Holla <sudeep.holla@....com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] arm64: take onlined cpus into account when setting
 irq affinity in migrate_one_irq



On 27/08/14 10:30, byungchul.park@....com wrote:
> From: Byungchul Park <byungchul.park@....com>
>
> This patch ensures that the cpu being offlined is not present in the affinity mask.
>

I agree that this patch fixes the issue reported in [1] without
disabling forced set affinity mask. However Thomas responded yesterday
asking to disable it [2] on the original thread for ARM. I have
responded on the thread and waiting for feedback from rmk and tglx. I
would prefer to wait and align with ARM code if possible.

> Signed-off-by: Byungchul Park <byungchul.park@....com>
> ---
>   arch/arm64/kernel/irq.c |    9 +++++++++
>   1 file changed, 9 insertions(+)
>
> diff --git a/arch/arm64/kernel/irq.c b/arch/arm64/kernel/irq.c
> index 473e5db..0c7b79e 100644
> --- a/arch/arm64/kernel/irq.c
> +++ b/arch/arm64/kernel/irq.c
> @@ -87,6 +87,7 @@ static bool migrate_one_irq(struct irq_desc *desc)
>   {
>   	struct irq_data *d = irq_desc_get_irq_data(desc);
>   	const struct cpumask *affinity = d->affinity;
> +	struct cpumask tmp_affinity;
>   	struct irq_chip *c;
>   	bool ret = false;
>
> @@ -100,6 +101,14 @@ static bool migrate_one_irq(struct irq_desc *desc)
>   	if (cpumask_any_and(affinity, cpu_online_mask) >= nr_cpu_ids) {
>   		affinity = cpu_online_mask;
>   		ret = true;
> +	} else {
> +		/*
> +		 * when using forced irq_set_affinity we must ensure that the cpu
> +		 * being offlined is not present in the affinity mask, it may be
> +		 * selected as the target CPU otherwise
> +		 */
> +		cpumask_and(&tmp_affinity, affinity, cpu_online_mask);

In case we decide to retain forced set affinity, you can probably squash 
this cpumask_and with the above cpumask_any_and.

> +		affinity = &tmp_affinity;
>   	}
>
>   	c = irq_data_get_irq_chip(d);
>

Regards,
Sudeep

[1] 
http://lists.infradead.org/pipermail/linux-arm-kernel/2014-June/266785.html
[2] 
http://lists.infradead.org/pipermail/linux-arm-kernel/2014-August/281548.html

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