While stressing EAS on my dragonboard RB3, I have noticed that LITTLE cores
where never selected as the most energy efficient CPU whatever the
utilization level of waking task.
energy model framework uses its cost field to estimate the energy with
the formula:
nrg = cost of the selected OPP * utilization / CPU's max capacity
which ends up selecting the CPU with lowest cost / max capacity ration
as long as the utilization fits in the OPP's capacity.
If we compare the cost of a little OPP with similar capacity of a big OPP
like :
OPP(kHz) OPP capacity cost max capacity cost/max capacity
LITTLE 1766400 407 351114 407 863
big 1056000 408 520267 1024 508
This can be interpreted as the LITTLE core consumes 70% more than big core
for the same compute capacity.
According to [1], LITTLE consumes 10% less than big core for Coremark
benchmark at those OPPs. If we consider that everything else stays
unchanged, the dynamic-power-coefficient of LITTLE core should be
only 53% of the current value: 290 * 53% = 154
Set the dynamic-power-coefficient of CPU0-3 to 154 to fix the energy model.
[1] https://github.com/kdrag0n/freqbench/tree/master/results/sdm845/main
Fixes: 0e0a8e35d725 ("arm64: dts: qcom: sdm845: correct dynamic power coefficients")
Signed-off-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
---
arch/arm64/boot/dts/qcom/sdm845.dtsi | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/arch/arm64/boot/dts/qcom/sdm845.dtsi b/arch/arm64/boot/dts/qcom/sdm845.dtsi
index 65032b94b46d..869bdb9bce6e 100644
--- a/arch/arm64/boot/dts/qcom/sdm845.dtsi
+++ b/arch/arm64/boot/dts/qcom/sdm845.dtsi
@@ -198,7 +198,7 @@ CPU0: cpu@0 {
reg = <0x0 0x0>;
enable-method = "psci";
capacity-dmips-mhz = <611>;
- dynamic-power-coefficient = <290>;
+ dynamic-power-coefficient = <154>;
qcom,freq-domain = <&cpufreq_hw 0>;
operating-points-v2 = <&cpu0_opp_table>;
interconnects = <&gladiator_noc MASTER_APPSS_PROC 3 &mem_noc SLAVE_EBI1 3>,
@@ -222,7 +222,7 @@ CPU1: cpu@100 {
reg = <0x0 0x100>;
enable-method = "psci";
capacity-dmips-mhz = <611>;
- dynamic-power-coefficient = <290>;
+ dynamic-power-coefficient = <154>;
qcom,freq-domain = <&cpufreq_hw 0>;
operating-points-v2 = <&cpu0_opp_table>;
interconnects = <&gladiator_noc MASTER_APPSS_PROC 3 &mem_noc SLAVE_EBI1 3>,
@@ -243,7 +243,7 @@ CPU2: cpu@200 {
reg = <0x0 0x200>;
enable-method = "psci";
capacity-dmips-mhz = <611>;
- dynamic-power-coefficient = <290>;
+ dynamic-power-coefficient = <154>;
qcom,freq-domain = <&cpufreq_hw 0>;
operating-points-v2 = <&cpu0_opp_table>;
interconnects = <&gladiator_noc MASTER_APPSS_PROC 3 &mem_noc SLAVE_EBI1 3>,
@@ -264,7 +264,7 @@ CPU3: cpu@300 {
reg = <0x0 0x300>;
enable-method = "psci";
capacity-dmips-mhz = <611>;
- dynamic-power-coefficient = <290>;
+ dynamic-power-coefficient = <154>;
qcom,freq-domain = <&cpufreq_hw 0>;
operating-points-v2 = <&cpu0_opp_table>;
interconnects = <&gladiator_noc MASTER_APPSS_PROC 3 &mem_noc SLAVE_EBI1 3>,
--
2.34.1
