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

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Date:   Thu, 16 Nov 2023 16:21:33 +0800
From:   maobibo <maobibo@...ngson.cn>
To:     WANG Xuerui <kernel@...0n.name>,
        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

Xuerui,

Thanks for reviewing my patch, and I reply inline.

On 2023/11/16 下午3:09, WANG Xuerui wrote:
> 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"
Will do in next patch.

>> 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?)
how about "prevent the vCPU from giving up scheduling"?

> 
>>
>> 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?
sure, will do in next version.

Regards
Bibo Mao
> 
>>
>> 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>
>