linux-kernel - Re: [PATCH 4/4] genirq: use irq's affinity for threaded irq with IRQF_RESCUE

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Date:   Fri, 6 Sep 2019 09:50:26 +0100
From:   John Garry <john.garry@...wei.com>
To:     Ming Lei <ming.lei@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>
CC:     <linux-kernel@...r.kernel.org>, Long Li <longli@...rosoft.com>,
        "Ingo Molnar" <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Keith Busch <keith.busch@...el.com>, Jens Axboe <axboe@...com>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        Hannes Reinecke <hare@...e.com>,
        <linux-nvme@...ts.infradead.org>, <linux-scsi@...r.kernel.org>,
        chenxiang <chenxiang66@...ilicon.com>,
        <daniel.lezcano@...aro.org>
Subject: Re: [PATCH 4/4] genirq: use irq's affinity for threaded irq with
 IRQF_RESCUE_THREAD

On 27/08/2019 09:53, Ming Lei wrote:
> In case of IRQF_RESCUE_THREAD, the threaded handler is only used to
> handle interrupt when IRQ flood comes, use irq's affinity for this thread
> so that scheduler may select other not too busy CPUs for handling the
> interrupt.
>
> Cc: Long Li <longli@...rosoft.com>
> Cc: Ingo Molnar <mingo@...hat.com>,
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Keith Busch <keith.busch@...el.com>
> Cc: Jens Axboe <axboe@...com>
> Cc: Christoph Hellwig <hch@....de>
> Cc: Sagi Grimberg <sagi@...mberg.me>
> Cc: John Garry <john.garry@...wei.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Hannes Reinecke <hare@...e.com>
> Cc: linux-nvme@...ts.infradead.org
> Cc: linux-scsi@...r.kernel.org
> Signed-off-by: Ming Lei <ming.lei@...hat.com>


> ---
>  kernel/irq/manage.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
> index 1566abbf50e8..03bc041348b7 100644
> --- a/kernel/irq/manage.c
> +++ b/kernel/irq/manage.c
> @@ -968,7 +968,18 @@ irq_thread_check_affinity(struct irq_desc *desc, struct irqaction *action)
>  	if (cpumask_available(desc->irq_common_data.affinity)) {
>  		const struct cpumask *m;
>
> -		m = irq_data_get_effective_affinity_mask(&desc->irq_data);
> +		/*
> +		 * Managed IRQ's affinity is setup gracefull on MUNA locality,

gracefully

> +		 * also if IRQF_RESCUE_THREAD is set, interrupt flood has been
> +		 * triggered, so ask scheduler to run the thread on CPUs
> +		 * specified by this interrupt's affinity.
> +		 */

Hi Ming,

> +		if ((action->flags & IRQF_RESCUE_THREAD) &&
> +				irqd_affinity_is_managed(&desc->irq_data))

This doesn't look to solve the other issue I reported - that being that 
we handle the interrupt in a threaded handler natively, and the hard 
irq+threaded handler fully occupies the cpu, limiting throughput.

So can we expand the scope to cover that scenario also? I don't think 
that it’s right to solve that separately. So if we're continuing this 
approach, can we add separate judgment for spreading the cpumask for the 
threaded part?

Thanks,
John

> +			m = desc->irq_common_data.affinity;
> +		else
> +			m = irq_data_get_effective_affinity_mask(
> +					&desc->irq_data);
>  		cpumask_copy(mask, m);
>  	} else {
>  		valid = false;
>