linux-kernel - Re: [RFC V2 7/8] powerpc: Enable IRQ generic entry/exit path.

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Message-ID: <589f259e-1db9-4ec2-accc-b27966d09a3e@linux.ibm.com>
Date: Tue, 16 Sep 2025 09:46:36 +0530
From: Shrikanth Hegde <sshegde@...ux.ibm.com>
To: Mukesh Kumar Chaurasiya <mchauras@...ux.ibm.com>, maddy@...ux.ibm.com,
        mpe@...erman.id.au, npiggin@...il.com, christophe.leroy@...roup.eu
Cc: oleg@...hat.com, kees@...nel.org, luto@...capital.net, wad@...omium.org,
        deller@....de, ldv@...ace.io, macro@...am.me.uk, charlie@...osinc.com,
        akpm@...ux-foundation.org, bigeasy@...utronix.de,
        ankur.a.arora@...cle.com, naveen@...nel.org,
        thomas.weissschuh@...utronix.de, Jason@...c4.com, peterz@...radead.org,
        tglx@...utronix.de, namcao@...utronix.de, kan.liang@...ux.intel.com,
        mingo@...nel.org, oliver.upton@...ux.dev, mark.barnett@....com,
        atrajeev@...ux.vnet.ibm.com, rppt@...nel.org, coltonlewis@...gle.com,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC V2 7/8] powerpc: Enable IRQ generic entry/exit path.



On 9/9/25 2:32 AM, Mukesh Kumar Chaurasiya wrote:
> Enable generic entry/exit path for ppc irq.
> 
> Signed-off-by: Mukesh Kumar Chaurasiya <mchauras@...ux.ibm.com>
> ---
>   arch/powerpc/Kconfig                    |   1 +
>   arch/powerpc/include/asm/entry-common.h |  93 ++---
>   arch/powerpc/include/asm/interrupt.h    | 492 +++---------------------
>   arch/powerpc/kernel/interrupt.c         |   9 +-
>   arch/powerpc/kernel/interrupt_64.S      |   2 -
>   5 files changed, 92 insertions(+), 505 deletions(-)
> 
								\
> diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c
> index f53d432f60870..7bb8a31b24ea7 100644
> --- a/arch/powerpc/kernel/interrupt.c
> +++ b/arch/powerpc/kernel/interrupt.c
> @@ -297,13 +297,8 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs)
>   		/* Returning to a kernel context with local irqs enabled. */
>   		WARN_ON_ONCE(!(regs->msr & MSR_EE));
>   again:
> -		if (need_irq_preemption()) {
> -			/* Return to preemptible kernel context */
> -			if (unlikely(read_thread_flags() & _TIF_NEED_RESCHED)) {
> -				if (preempt_count() == 0)
> -					preempt_schedule_irq();
> -			}
> -		}
> +		if (need_irq_preemption())
> +			irqentry_exit_cond_resched();

irqentry_exit_cond_resched is also called in irqentry_exit. It would be 
better if we can find ways to avoid calling it again.

I see a loop here. But comment says it is not enabling irq again. so the 
loop is bounded. So might be okay to remove cond_resched here. do run
preemptirq, irq tracers to ensure that is case.

Also, what is this "soft_interrupts"?

>   
>   		check_return_regs_valid(regs);
>   
> diff --git a/arch/powerpc/kernel/interrupt_64.S b/arch/powerpc/kernel/interrupt_64.S
> index 1ad059a9e2fef..6aa88fe91fb6a 100644
> --- a/arch/powerpc/kernel/interrupt_64.S
> +++ b/arch/powerpc/kernel/interrupt_64.S
> @@ -418,8 +418,6 @@ _ASM_NOKPROBE_SYMBOL(interrupt_return_\srr\())
>   	beq	interrupt_return_\srr\()_kernel
>   interrupt_return_\srr\()_user: /* make backtraces match the _kernel variant */
>   _ASM_NOKPROBE_SYMBOL(interrupt_return_\srr\()_user)
> -	addi	r3,r1,STACK_INT_FRAME_REGS
> -	bl	CFUNC(interrupt_exit_user_prepare)
>   #ifndef CONFIG_INTERRUPT_SANITIZE_REGISTERS
>   	cmpdi	r3,0
>   	bne-	.Lrestore_nvgprs_\srr