linux-kernel - [PATCH 7/7] arm: dts: vexpress-v2p-ca15_a7: Add cpu dynamic-power-coefficient information

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Date:   Mon, 28 Jan 2019 16:55:22 +0000
From:   Quentin Perret <quentin.perret@....com>
To:     rjw@...ysocki.net, viresh.kumar@...aro.org, sudeep.holla@....com,
        liviu.dudau@....com, lorenzo.pieralisi@....com, robh+dt@...nel.org,
        mark.rutland@....com, nm@...com, sboyd@...nel.org
Cc:     linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        dietmar.eggemann@....com, mka@...omium.org, quentin.perret@....com
Subject: [PATCH 7/7] arm: dts: vexpress-v2p-ca15_a7: Add cpu dynamic-power-coefficient information

From: Dietmar Eggemann <dietmar.eggemann@....com>

A CPUfreq driver, like the ARM big.LITTLE driver used on the TC2 board,
which provide the Energy Model with power cost information via the
PM_OPP of_dev_pm_opp_get_cpu_power() function, do need the
dynamic-power-coefficient (C) in the device tree.

Method used to obtain the C value:
C is computed by measuring energy (E) consumption of a frequency domain
(FD) over a 10s runtime (t) sysbench workload running at each Operating
Performance Point (OPP) affine to 1 or 2 CPUs of that FD while the other
CPUs of the system are hotplugged out.
By definition all CPUs of a FD have the the same micro-architecture. An
OPP is characterized by a certain frequency (f) and voltage (V) value.
The corresponding power values (P) are calculated by dividing the delta
of the E values between the runs with 2 and 1 CPUs by t.

With n data tuples (P, f, V), n equal to number of OPPs for this
frequency domain, we can solve C by:

P = Pstat + Pdyn

P = Pstat + CV²f

Cx = (Px - P1)/(Vx²fx - V1²f1) with x = {2, ..., n}

The C value is the arithmetic mean out of {C2, ..., Cn}.

Signed-off-by: Dietmar Eggemann <dietmar.eggemann@....com>
Signed-off-by: Quentin Perret <quentin.perret@....com>
---
 arch/arm/boot/dts/vexpress-v2p-ca15_a7.dts | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/arm/boot/dts/vexpress-v2p-ca15_a7.dts b/arch/arm/boot/dts/vexpress-v2p-ca15_a7.dts
index a2ccacd07f4f..00cd9f5bef2e 100644
--- a/arch/arm/boot/dts/vexpress-v2p-ca15_a7.dts
+++ b/arch/arm/boot/dts/vexpress-v2p-ca15_a7.dts
@@ -42,6 +42,7 @@
 			cci-control-port = <&cci_control1>;
 			cpu-idle-states = <&CLUSTER_SLEEP_BIG>;
 			capacity-dmips-mhz = <1024>;
+			dynamic-power-coefficient = <990>;
 		};

 		cpu1: cpu@1 {
@@ -51,6 +52,7 @@
 			cci-control-port = <&cci_control1>;
 			cpu-idle-states = <&CLUSTER_SLEEP_BIG>;
 			capacity-dmips-mhz = <1024>;
+			dynamic-power-coefficient = <990>;
 		};

 		cpu2: cpu@2 {
@@ -60,6 +62,7 @@
 			cci-control-port = <&cci_control2>;
 			cpu-idle-states = <&CLUSTER_SLEEP_LITTLE>;
 			capacity-dmips-mhz = <516>;
+			dynamic-power-coefficient = <133>;
 		};

 		cpu3: cpu@3 {
@@ -69,6 +72,7 @@
 			cci-control-port = <&cci_control2>;
 			cpu-idle-states = <&CLUSTER_SLEEP_LITTLE>;
 			capacity-dmips-mhz = <516>;
+			dynamic-power-coefficient = <133>;
 		};

 		cpu4: cpu@4 {
@@ -78,6 +82,7 @@
 			cci-control-port = <&cci_control2>;
 			cpu-idle-states = <&CLUSTER_SLEEP_LITTLE>;
 			capacity-dmips-mhz = <516>;
+			dynamic-power-coefficient = <133>;
 		};

 		idle-states {
-- 
2.20.1