linux-kernel - Re: [PATCH 3/6] genirq: soft_moderation: activate hooks in handle_irq

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Message-ID: <87tsyycllk.ffs@tglx>
Date: Thu, 13 Nov 2025 10:45:11 +0100
From: Thomas Gleixner <tglx@...utronix.de>
To: Luigi Rizzo <lrizzo@...gle.com>, Marc Zyngier <maz@...nel.org>, Luigi
 Rizzo <rizzo.unipi@...il.com>, Paolo Abeni <pabeni@...hat.com>, Andrew
 Morton <akpm@...ux-foundation.org>, Sean Christopherson
 <seanjc@...gle.com>, Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc: linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org, Bjorn Helgaas
 <bhelgaas@...gle.com>, Willem de Bruijn <willemb@...gle.com>, Luigi Rizzo
 <lrizzo@...gle.com>
Subject: Re: [PATCH 3/6] genirq: soft_moderation: activate hooks in
 handle_irq_event()

On Wed, Nov 12 2025 at 19:24, Luigi Rizzo wrote:

Forgot to mention it on the earlier patches. The subject line is wrong
in multiple aspects. See documentation.

>  arch/x86/kernel/cpu/common.c | 1 +
>  drivers/irqchip/irq-gic-v3.c | 2 ++

How are those related to the subject? 

>  kernel/irq/handle.c          | 3 +++
>  kernel/irq/irqdesc.c         | 1 +
>  4 files changed, 7 insertions(+)
>
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index 02d97834a1d4d..1953419fde6ff 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -2440,6 +2440,7 @@ void cpu_init(void)
>  
>  		intel_posted_msi_init();
>  	}
> +	irq_moderation_percpu_init();

Why is this called in architecture specific code? There is absolutely
nothing architecture specific about this. The CPU hotplug infrastructure
can handle this just fine in a generic way.
  
>  #include <asm/irq_regs.h>
> @@ -254,9 +255,11 @@ irqreturn_t handle_irq_event(struct irq_desc *desc)
>  	irqd_set(&desc->irq_data, IRQD_IRQ_INPROGRESS);
>  	raw_spin_unlock(&desc->lock);
>  
> +	irq_moderation_hook(desc); /* may disable irq so must run unlocked */

That's just wrong. That can trivially be implemented in a way which
works with the lock held.

>  	ret = handle_irq_event_percpu(desc);
>  	raw_spin_lock(&desc->lock);
> +	irq_moderation_epilogue(desc); /* start moderation timer if needed */
>  	irqd_clear(&desc->irq_data, IRQD_IRQ_INPROGRESS);
>  	return ret;
>  }
> diff --git a/kernel/irq/irqdesc.c b/kernel/irq/irqdesc.c
> index db714d3014b5f..e3efbecf5b937 100644
> --- a/kernel/irq/irqdesc.c
> +++ b/kernel/irq/irqdesc.c
> @@ -134,6 +134,7 @@ static void desc_set_defaults(unsigned int irq, struct irq_desc *desc, int node,
>  	desc->tot_count = 0;
>  	desc->name = NULL;
>  	desc->owner = owner;
> +	irq_moderation_init_fields(desc);

That's clearly part of activation in handle_irq_event() ....

Thanks

        tglx