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Subject: Re: [PATCH] LoongArch: Implement stable timer shutdown interface
To:     Huacai Chen <chenhuacai@kernel.org>
Cc:     WANG Xuerui <kernel@xen0n.name>,
        Peter Zijlstra <peterz@infradead.org>,
        loongarch@lists.linux.dev, linux-kernel@vger.kernel.org
References: <20231114114656.1003841-1-maobibo@loongson.cn>
 <CAAhV-H46vueDp0ffTuD6sO=xWVsbcwVDBzFU7QirE9JwOWd4dg@mail.gmail.com>
From:   maobibo <maobibo@loongson.cn>
Message-ID: <aebb1335-6398-07ba-089b-ec74899de6b0@loongson.cn>
Date:   Thu, 16 Nov 2023 11:17:42 +0800
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On 2023/11/16 上午10:50, Huacai Chen wrote:
> Hi, Bibo,
> 
> "stable timer" is Chinglish, use "constant timer" here.
will do if you insist on, the name is not created by me :(

> 
> On Tue, Nov 14, 2023 at 7:49 PM Bibo Mao <maobibo@loongson.cn> wrote:
>>
>> When cpu is hotplug out, cpu is in idle state and function
>> 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.
>>
>> This patch adds detailed implementation for timer shutdown interface, so
>> that timer will be disabled when cpu is plug-out.
>>
>> Signed-off-by: Bibo Mao <maobibo@loongson.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;
>>
> Please remove the whole constant_set_state_oneshot_stopped() and move
> its logic to the below constant_set_state_shutdown().
will do.
> 
> And it is very strange that this "bug" hasn't caused any problems until now.
Since there is no other hw timer except percpu timer, there will be 
problem if hw timer is switched, also nobody watches hw behaviors when 
cpu is plug-out. LTP cpu hotplug test cases just report passed on 
physical machine.

Regards
Bibo Mao

> 
> Huacai
> 
>> @@ -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
>> --
>> 2.39.3
>>