linux-kernel - RE: [PATCH v2 07/13] x86/irq: Factor out calling ISR from common

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Date: Fri, 12 Apr 2024 09:21:45 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Jacob Pan <jacob.jun.pan@...ux.intel.com>, LKML
	<linux-kernel@...r.kernel.org>, X86 Kernel <x86@...nel.org>, Peter Zijlstra
	<peterz@...radead.org>, "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	Thomas Gleixner <tglx@...utronix.de>, Lu Baolu <baolu.lu@...ux.intel.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>, "Hansen, Dave"
	<dave.hansen@...el.com>, Joerg Roedel <joro@...tes.org>, "H. Peter Anvin"
	<hpa@...or.com>, Borislav Petkov <bp@...en8.de>, Ingo Molnar
	<mingo@...hat.com>
CC: "Luse, Paul E" <paul.e.luse@...el.com>, "Williams, Dan J"
	<dan.j.williams@...el.com>, Jens Axboe <axboe@...nel.dk>, "Raj, Ashok"
	<ashok.raj@...el.com>, "maz@...nel.org" <maz@...nel.org>, "seanjc@...gle.com"
	<seanjc@...gle.com>, Robin Murphy <robin.murphy@....com>,
	"jim.harris@...sung.com" <jim.harris@...sung.com>, "a.manzanares@...sung.com"
	<a.manzanares@...sung.com>, Bjorn Helgaas <helgaas@...nel.org>, "Zeng, Guang"
	<guang.zeng@...el.com>, "robert.hoo.linux@...il.com"
	<robert.hoo.linux@...il.com>
Subject: RE: [PATCH v2 07/13] x86/irq: Factor out calling ISR from
 common_interrupt

> From: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> Sent: Saturday, April 6, 2024 6:31 AM
> 
> Prepare for calling external IRQ handlers directly from the posted MSI
> demultiplexing loop. Extract the common code with common interrupt to
> avoid code duplication.
> 
> Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> ---
>  arch/x86/kernel/irq.c | 23 ++++++++++++++---------
>  1 file changed, 14 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
> index f39f6147104c..c54de9378943 100644
> --- a/arch/x86/kernel/irq.c
> +++ b/arch/x86/kernel/irq.c
> @@ -242,18 +242,10 @@ static __always_inline void handle_irq(struct
> irq_desc *desc,
>  		__handle_irq(desc, regs);
>  }
> 
> -/*
> - * common_interrupt() handles all normal device IRQ's (the special SMP
> - * cross-CPU interrupts have their own entry points).
> - */
> -DEFINE_IDTENTRY_IRQ(common_interrupt)
> +static __always_inline void call_irq_handler(int vector, struct pt_regs *regs)
>  {
> -	struct pt_regs *old_regs = set_irq_regs(regs);
>  	struct irq_desc *desc;
> 
> -	/* entry code tells RCU that we're not quiescent.  Check it. */
> -	RCU_LOCKDEP_WARN(!rcu_is_watching(), "IRQ failed to wake up
> RCU");
> -
>  	desc = __this_cpu_read(vector_irq[vector]);
>  	if (likely(!IS_ERR_OR_NULL(desc))) {
>  		handle_irq(desc, regs);

the hidden lines has one problem:

	} else {
		apic_eoi();

		if (desc == VECTOR_UNUSED) {
			...

there will be two EOI's for unused vectors, adding the one
in sysvec_posted_msi_notification().