linux-kernel - Re: Loongson (and other $ARCHs?) idle VS timer enqueue

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Date:   Sat, 22 Apr 2023 16:21:45 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Huacai Chen <chenhuacai@...nel.org>,
        WANG Xuerui <kernel@...0n.name>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Anna-Maria Behnsen <anna-maria@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: Loongson (and other $ARCHs?) idle VS timer enqueue

On Sat, Apr 22, 2023 at 10:17:00AM +0200, Peter Zijlstra wrote:
> diff --git a/arch/loongarch/kernel/genex.S b/arch/loongarch/kernel/genex.S
> index 44ff1ff64260..5a102ff80de0 100644
> --- a/arch/loongarch/kernel/genex.S
> +++ b/arch/loongarch/kernel/genex.S
> @@ -40,6 +40,7 @@ SYM_FUNC_START(handle_vint)
>  	ori	t0, t0, 0x1f
>  	xori	t0, t0, 0x1f
>  	bne	t0, t1, 1f
> +	addi.d	t0, t0, 0x20
>  	LONG_S	t0, sp, PT_ERA
>  1:	move	a0, sp
>  	move	a1, sp

But the interrupts are enabled in C from arch_cpu_idle(), which
only then calls the ASM __arch_cpu_idle(). So if the interrupt happens
somewhere in between the call, the rollback (or fast-forward now)
doesn't apply.

I guess interrupts need to be re-enabled from ASM in the beginning
of __arch_cpu_idle() so that it's part of the fast-forward region.

> diff --git a/arch/mips/kernel/genex.S b/arch/mips/kernel/genex.S
> index b6de8e88c1bd..cd6aae441ad9 100644
> --- a/arch/mips/kernel/genex.S
> +++ b/arch/mips/kernel/genex.S
> @@ -140,6 +140,7 @@ LEAF(__r4k_wait)
>  	ori	k0, 0x1f	/* 32 byte rollback region */
>  	xori	k0, 0x1f
>  	bne	k0, k1, \handler
> +	addiu	k0, 0x20
>  	MTC0	k0, CP0_EPC
>  	.set pop
>  	.endm

The same seem to apply with interrupts being re-enabled by r4k_wait().

Thanks.