[PATCH] cpuidle: mvebu: update cpuidle thresholds for Armada XP SOCs

[Gregory CLEMENT]

Le 10 mars 2015 19:35:19 GMT+01:00, Daniel Lezcano <daniel.lezcano at linaro.org> a écrit :
>On 03/10/2015 07:05 PM, Thomas Petazzoni wrote:
>> Hello Daniel,
>>
>> I know you suggested a more rigorous method of determining the exit
>> latency and target residency times, but would it be nonetheless
>> possible to apply this patch, which clearly improves performance a
>lot,
>> and actually makes the code match the values used in the vendor
>kernel?
>>
>> I also think this patch should be marked for stable, it fixes values
>> introduced in commit b858fbc1919720f7f54360098ece03b383e961fa, and
>> should therefore be backported all the way to v3.16.
>
>I don't have a problem to apply this patch. But I would like to have 
>confirmation from one of the Armada maintainers the tradeoff is
>accepted 
>(less energy saving for more performance).

Hi Daniel,

I already gave my acked- by for this patch, so for me this tradeoff
is acceptable.

Grégory

>
>
>> On Fri, 13 Feb 2015 15:55:03 +0100 (CET), s. rannou wrote:
>>> Originally, the thresholds used in the cpuidle driver for Armada
>SOCs
>>> were temporarily chosen, leaving room for improvements.
>>>
>>> This commit updates the thresholds for the Armada XP SOCs with
>values
>>> that positively impact performances:
>>>
>>>                                  without patch  with patch   vendor
>kernel
>>>   - iperf localhost (gbit/sec)   ~3.7           ~6.4         ~5.4
>>>   - ioping tmpfs (iops)          ~163k          ~206k        ~179k
>>>   - ioping tmpfs (mib/s)         ~636           ~805         ~699
>>>
>>> The idle power consumption is negatively impacted (proportionally
>less
>>> than the performance gain), and we are still performing better than
>>> the vendor kernel here:
>>>
>>>                                  without patch   with patch  vendor
>kernel
>>>   - power consumption idle (W)   ~2.4            ~3.2        ~4.4
>>>   - power consumption busy (W)   ~8.6            ~8.3        ~8.6
>>>
>>> There is still room for improvement regarding the value of these
>>> thresholds, they were chosen to mimic the vendor kernel.
>>>
>>> This patch only impacts Armada XP SOCs and was tested on Online Labs
>>> C1 boards. A similar approach can be taken to improve the
>performances
>>> of the Armada 370 and Armada 38x SOCs.
>>>
>>> Thanks a lot to Thomas Petazzoni, Gregory Clement and Willy Tarreau
>>> for the discussions and tips around this topic.
>>>
>>> Signed-off-by: Sebastien Rannou <mxs at sbrk.org>
>>> ---
>>>   drivers/cpuidle/cpuidle-mvebu-v7.c | 8 ++++----
>>>   1 file changed, 4 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/cpuidle/cpuidle-mvebu-v7.c
>b/drivers/cpuidle/cpuidle-mvebu-v7.c
>>> index 38e6861..3716a1f 100644
>>> --- a/drivers/cpuidle/cpuidle-mvebu-v7.c
>>> +++ b/drivers/cpuidle/cpuidle-mvebu-v7.c
>>> @@ -50,17 +50,17 @@ static struct cpuidle_driver
>armadaxp_idle_driver = {
>>>   	.states[0]		= ARM_CPUIDLE_WFI_STATE,
>>>   	.states[1]		= {
>>>   		.enter			= mvebu_v7_enter_idle,
>>> -		.exit_latency		= 10,
>>> +		.exit_latency		= 100,
>>>   		.power_usage		= 50,
>>> -		.target_residency	= 100,
>>> +		.target_residency	= 1000,
>>>   		.name			= "MV CPU IDLE",
>>>   		.desc			= "CPU power down",
>>>   	},
>>>   	.states[2]		= {
>>>   		.enter			= mvebu_v7_enter_idle,
>>> -		.exit_latency		= 100,
>>> +		.exit_latency		= 1000,
>>>   		.power_usage		= 5,
>>> -		.target_residency	= 1000,
>>> +		.target_residency	= 10000,
>>>   		.flags			= MVEBU_V7_FLAG_DEEP_IDLE,
>>>   		.name			= "MV CPU DEEP IDLE",
>>>   		.desc			= "CPU and L2 Fabric power down",
>>
>>
>>
>
>
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-- 
Gregory Clement, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com