[PATCH] at91: cpuidle: Fix target_residency

[Daniel Lezcano]

On 06/21/2013 06:11 PM, Nicolas Ferre wrote:
> On 21/06/2013 17:44, Daniel Lezcano :
>> On 06/21/2013 04:48 PM, Nicolas Ferre wrote:
>>> On 21/06/2013 15:22, Daniel Lezcano :
>>>> On 06/21/2013 03:20 PM, Nicolas Ferre wrote:
>>>>> On 21/06/2013 14:36, Daniel Lezcano :
>>>>>> The following commit:
>>>>>>
>>>>>> commit 7e348b9012522fa0efd854d20d210d5e57fcedd1
>>>>>> Author: Robert Lee <rob.lee at linaro.org>
>>>>>> Date:   Tue Mar 20 15:22:43 2012 -0500
>>>>>>
>>>>>>        ARM: at91: Consolidate time keeping and irq enable
>>>>>>
>>>>>>        Enable core cpuidle timekeeping and irq enabling and remove
>>>>>> that
>>>>>>        handling from this code.
>>>>>>
>>>>>> introduced a zero to the state1 (suspend) target residency.
>>>>>>
>>>>>> [ ... ]
>>>>>>
>>>>>> +       .states[1]              = {
>>>>>> +               .enter                  = at91_enter_idle,
>>>>>> +               .exit_latency           = 10,
>>>>>> +               .target_residency       = 100000,
>>>>>> +               .flags                  = CPUIDLE_FLAG_TIME_VALID,
>>>>>> +               .name                   = "RAM_SR",
>>>>>> +               .desc                   = "WFI and DDR Self Refresh",
>>>>>> +       },
>>>>>>
>>>>>> [ ... ]
>>>>>>
>>>>>> -       /* Wait for interrupt and RAM self refresh state */
>>>>>> -       driver->states[1].enter = at91_enter_idle;
>>>>>> -       driver->states[1].exit_latency = 10;
>>>>>> -       driver->states[1].target_residency = 10000;
>>>>>> -       driver->states[1].flags = CPUIDLE_FLAG_TIME_VALID;
>>>>>> -       strcpy(driver->states[1].name, "RAM_SR");
>>>>>> -       strcpy(driver->states[1].desc, "WFI and RAM Self Refresh");
>>>>>>
>>>>>> [ ... ]
>>>>>>
>>>>>> The cpuidle never enters this state since this commit.
>>>>
>>>> To be a bit more precise. With a periodic tick, the cpu never enters
>>>> the
>>>> state1 with both 10000 and 100000.
>>>>
>>>> With a tickless system, it enters to state1 much more often with the
>>>> initial value, roughly x7 more.
>>>
>>> BTW Daniel, I think I can stack this patch on my fixes-non-critical
>>> branch for 3.11: do you think that I should push for making it accepted
>>> for 3.10 (even if it seems very late)?
>>
>> Yes, I think it should go for 3.10 as it is fix and also for 3.9.8
>> (stable). May be I should have Cc stable@ ...
> 
> Well, so it doesn't sound like a regression if it was already present in
> 3.9...

Or the regression is there since 3.5 and detected today :)

> Moreover, it does not seem to be taken into account for all
> configuration (seems not triggered for !tickless kernels).

The periodic tick is IIRC, 100Hz, so 10ms, the same value as the idle
state1 target residency, the governor won't use this state in any case
because the next scheduled event occurs before the target residency. If
it would have been, let's say, 8.5ms, or the periodic tick 50Hz, then it
would have been picked up.

> So I suspect Arnd and Olof would not take it for 3.10-fixes...
> 
> Guys, you thoughts?
> 
> 
>>>> BTW, I am surpised with a sam926*, CONFIG_NO_HZ=y is not in the default
>>>> config.
>>>
>>> Yes, indeed: we have to consider it.
>>>
>>> Best regards,
>>>
>>>>>> Fix it by setting the value to 10ms again.
>>>>>>
>>>>>> Signed-off-by: Daniel Lezcano <daniel.lezcano at linaro.org>
>>>>>
>>>>> Acked-by: Nicolas Ferre <nicolas.ferre at atmel.com>
>>>>>
>>>>>> ---
>>>>>>     arch/arm/mach-at91/cpuidle.c |    2 +-
>>>>>>     1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/arch/arm/mach-at91/cpuidle.c
>>>>>> b/arch/arm/mach-at91/cpuidle.c
>>>>>> index 69f9e3b..4ec6a6d 100644
>>>>>> --- a/arch/arm/mach-at91/cpuidle.c
>>>>>> +++ b/arch/arm/mach-at91/cpuidle.c
>>>>>> @@ -51,7 +51,7 @@ static struct cpuidle_driver at91_idle_driver = {
>>>>>>         .states[1]        = {
>>>>>>             .enter            = at91_enter_idle,
>>>>>>             .exit_latency        = 10,
>>>>>> -        .target_residency    = 100000,
>>>>>> +        .target_residency    = 10000,
>>>>>>             .flags            = CPUIDLE_FLAG_TIME_VALID,
>>>>>>             .name            = "RAM_SR",
>>>>>>             .desc            = "WFI and DDR Self Refresh",
>>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>
>>>
>>
>>
> 
> 


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