linux-kernel - Re: [PATCH] LoongArch: Implement stable timer shutdown interface

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Date:   Thu, 16 Nov 2023 15:09:05 +0800
From:   WANG Xuerui <kernel@...0n.name>
To:     Bibo Mao <maobibo@...ngson.cn>, Huacai Chen <chenhuacai@...nel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>, loongarch@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] LoongArch: Implement stable timer shutdown interface

Hi,

Sorry for the late review but here we go:

On 11/14/23 19:46, Bibo Mao wrote:
> When cpu is hotplug out, cpu is in idle state and function
"When a CPU is hot-unplugged, it is put into idle state and the function 
... is called"
> arch_cpu_idle_dead is called. Timer interrupt for this processor should
> be disabled, else there will be timer interrupt for the dead cpu. Also
> this prevents vcpu to schedule out during halt-polling flow when system
> is running in vm mode, since there is pending timer interrupt.

The logical relationship is a bit unclear, is my paraphrasing correct in 
your opinion?

"Timer interrupt for this processor should be disabled, else a pending 
timer interrupt will prevent the vCPU from scheduling out during the 
halt-polling flow when system is running in VM mode"

(I don't immediately know what a "schedule out" is. Is that a 
translation artifact or some KVM jargon?)

>
> This patch adds detailed implementation for timer shutdown interface, so
> that timer will be disabled when cpu is plug-out.

Missing some definite articles too.

"This patch implements the timer shutdown interface so that the timer 
will be properly disabled when a CPU is hot-unplugged"

Is this version better?

>
> Signed-off-by: Bibo Mao <maobibo@...ngson.cn>
> ---
>   arch/loongarch/kernel/time.c | 9 ++-------
>   1 file changed, 2 insertions(+), 7 deletions(-)
>
> diff --git a/arch/loongarch/kernel/time.c b/arch/loongarch/kernel/time.c
> index 3064af94db9c..2920770e30a9 100644
> --- a/arch/loongarch/kernel/time.c
> +++ b/arch/loongarch/kernel/time.c
> @@ -58,7 +58,7 @@ static int constant_set_state_oneshot(struct clock_event_device *evt)
>   	return 0;
>   }
>   
> -static int constant_set_state_oneshot_stopped(struct clock_event_device *evt)
> +static int constant_set_state_shutdown(struct clock_event_device *evt)
>   {
>   	unsigned long timer_config;
>   
> @@ -90,11 +90,6 @@ static int constant_set_state_periodic(struct clock_event_device *evt)
>   	return 0;
>   }
>   
> -static int constant_set_state_shutdown(struct clock_event_device *evt)
> -{
> -	return 0;
> -}
> -
>   static int constant_timer_next_event(unsigned long delta, struct clock_event_device *evt)
>   {
>   	unsigned long timer_config;
> @@ -161,7 +156,7 @@ int constant_clockevent_init(void)
>   	cd->rating = 320;
>   	cd->cpumask = cpumask_of(cpu);
>   	cd->set_state_oneshot = constant_set_state_oneshot;
> -	cd->set_state_oneshot_stopped = constant_set_state_oneshot_stopped;
> +	cd->set_state_oneshot_stopped = constant_set_state_shutdown;
>   	cd->set_state_periodic = constant_set_state_periodic;
>   	cd->set_state_shutdown = constant_set_state_shutdown;
>   	cd->set_next_event = constant_timer_next_event;
>
> base-commit: 9bacdd8996c77c42ca004440be610692275ff9d0

Otherwise LGTM (regarding the renaming of 
constant_set_state_oneshot_stopped, both it and the removed 
constant_set_state_shutdown only has one usage respectively, and looking 
at the function body it's arguably more appropriate to let it take the 
"shutdown" name: it's just clearing the enable bit from the CSR.TCFG and 
nothing else).

With the nits addressed:

Reviewed-by: WANG Xuerui <git@...0n.name>

-- 
WANG "xen0n" Xuerui

Linux/LoongArch mailing list: https://lore.kernel.org/loongarch/