linux-kernel - Re: [PATCH] cpuidle: menu: Fix long delay issue when tick stopped

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Date:   Thu, 27 Jan 2022 09:43:56 +0800
From:   Shaokun Zhang <zhangshaokun@...ilicon.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
CC:     Linux PM <linux-pm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Guo Yang <guoyang2@...wei.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: Re: [PATCH] cpuidle: menu: Fix long delay issue when tick stopped

Hi Rafael,

Apologies that reply later.

On 2022/1/21 2:55, Rafael J. Wysocki wrote:
> On Mon, Jan 17, 2022 at 9:16 AM Shaokun Zhang
> <zhangshaokun@...ilicon.com> wrote:
>>

...<snip>...

>> [   37.083307] intervals = 35us
>> [   37.083320] target_residency_ns = 10000, predicted_ns = 35482140
>> [   37.083349] target_residency_ns = 600000, predicted_ns = 35482140
>>
>> Add idle tick wakeup judge before change predicted_ns.
>>
>> Cc: "Rafael J. Wysocki" <rafael@...nel.org>
>> Cc: Daniel Lezcano <daniel.lezcano@...aro.org>
>> Signed-off-by: Guo Yang <guoyang2@...wei.com>
>> Signed-off-by: Shaokun Zhang <zhangshaokun@...ilicon.com>
>> ---
>>  drivers/cpuidle/governors/menu.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
>> index c492268..3f03843 100644
>> --- a/drivers/cpuidle/governors/menu.c
>> +++ b/drivers/cpuidle/governors/menu.c
>> @@ -313,7 +313,7 @@ static int menu_select(struct cpuidle_driver *drv, struct cpuidle_device *dev,
>>                                 get_typical_interval(data, predicted_us)) *
>>                                 NSEC_PER_USEC;
>>
>> -       if (tick_nohz_tick_stopped()) {
>> +       if (tick_nohz_tick_stopped() && data->tick_wakeup) {
> 
> data->tick_wakeup is only true if tick_nohz_idle_got_tick() has
> returned true, but I'm not sure how this can happen after stopping the
> tick.

In order to debug this, call trace is added and as follow:

if (predicted_us < TICK_USEC)
    predicted_us = ktime_to_us(delta_next);
    printk("predicted_us = %uus\n", predicted_us);
    dump_stack(); //add call trace print
}

When the issue came, the CPU was waken up by network interrupts
[ 1048.130033] intervals = 1us
[ 1048.130034] intervals = 1us
[ 1048.130035] intervals = 1us
[ 1048.130036] intervals = 1us
[ 1048.130037] intervals = 1us
[ 1048.130038] intervals = 1us
[ 1048.130039] intervals = 1us
[ 1048.130040] intervals = 1us
[ 1048.130041] predicted_us = 484143us
[ 1048.130043] CPU: 3 PID: 0 Comm: swapper/3 Tainted: G           OE     5.3.0-rc6 #23
[ 1048.130044] Hardware name: Huawei 2288H V5/BC11SPSCB0, BIOS 0.39 12/01/2017
[ 1048.130045] Call Trace:
[ 1048.130048]  dump_stack+0x5a/0x73
[ 1048.130052]  menu_select+0x3b0/0x6c0
[ 1048.130058]  do_idle+0x1b4/0x290
[ 1048.130063]  cpu_startup_entry+0x19/0x20
[ 1048.130067]  start_secondary+0x155/0x1b0
[ 1048.130070]  secondary_startup_64+0xa4/0xb0
[ 1048.130078] intervals = 1us
[ 1048.130079] intervals = 1us
[ 1048.130080] intervals = 1us
[ 1048.130081] intervals = 1us
[ 1048.130081] intervals = 1us
[ 1048.130082] intervals = 1us
[ 1048.130083] intervals = 1us
[ 1048.130084] intervals = 1us
[ 1048.130085] predicted_us = 484097us
[ 1048.130087] CPU: 3 PID: 0 Comm: swapper/3 Tainted: G           OE     5.3.0-rc6 #23
[ 1048.130088] Hardware name: Huawei 2288H V5/BC11SPSCB0, BIOS 0.39 12/01/2017
[ 1048.130089] Call Trace:
[ 1048.130093]  dump_stack+0x5a/0x73
[ 1048.130097]  menu_select+0x3b0/0x6c0
[ 1048.130102]  do_idle+0x1b4/0x290
[ 1048.130107]  cpu_startup_entry+0x19/0x20
[ 1048.130112]  start_secondary+0x155/0x1b0
[ 1048.130115]  secondary_startup_64+0xa4/0xb0
[ 1048.130123] intervals = 1us
[ 1048.130123] intervals = 1us
[ 1048.130124] intervals = 1us
[ 1048.130125] intervals = 1us
[ 1048.130126] intervals = 1us
[ 1048.130127] intervals = 1us
[ 1048.130128] intervals = 1us
[ 1048.130129] intervals = 1us
[ 1048.130130] predicted_us = 484053us
[ 1048.130132] CPU: 3 PID: 0 Comm: swapper/3 Tainted: G           OE     5.3.0-rc6 #23
[ 1048.130133] Hardware name: Huawei 2288H V5/BC11SPSCB0, BIOS 0.39 12/01/2017
[ 1048.130134] Call Trace:
[ 1048.130137]  dump_stack+0x5a/0x73
[ 1048.130141]  menu_select+0x3b0/0x6c0
[ 1048.130147]  do_idle+0x1b4/0x290
[ 1048.130152]  cpu_startup_entry+0x19/0x20
[ 1048.130156]  start_secondary+0x155/0x1b0
[ 1048.130159]  secondary_startup_64+0xa4/0xb0

> 
> IOW, it looks like the change simply makes the condition be always false.
> 

Agree, any good feedback is welcome and we can try it.

Thanks,
Shaokun

>>                 /*
>>                  * If the tick is already stopped, the cost of possible short
>>                  * idle duration misprediction is much higher, because the CPU
>> --
>> 1.8.3.1
>>
> .
>