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

[Thomas Petazzoni]

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.

Thanks a lot,

Thomas

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",



-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com