@@ -36,6 +36,7 @@
cooling-min-level = <0>;
cooling-max-level = <11>;
#cooling-cells = <2>; /* min followed by max */
+ capacity-dmips-mhz = <1024>;
};
cpu1: cpu@1 {
@@ -48,6 +49,7 @@
cooling-min-level = <0>;
cooling-max-level = <11>;
#cooling-cells = <2>; /* min followed by max */
+ capacity-dmips-mhz = <1024>;
};
cpu2: cpu@2 {
@@ -60,6 +62,7 @@
cooling-min-level = <0>;
cooling-max-level = <11>;
#cooling-cells = <2>; /* min followed by max */
+ capacity-dmips-mhz = <1024>;
};
cpu3: cpu@3 {
@@ -72,6 +75,7 @@
cooling-min-level = <0>;
cooling-max-level = <11>;
#cooling-cells = <2>; /* min followed by max */
+ capacity-dmips-mhz = <1024>;
};
cpu4: cpu@100 {
@@ -85,6 +89,7 @@
cooling-min-level = <0>;
cooling-max-level = <7>;
#cooling-cells = <2>; /* min followed by max */
+ capacity-dmips-mhz = <539>;
};
cpu5: cpu@101 {
@@ -97,6 +102,7 @@
cooling-min-level = <0>;
cooling-max-level = <7>;
#cooling-cells = <2>; /* min followed by max */
+ capacity-dmips-mhz = <539>;
};
cpu6: cpu@102 {
@@ -109,6 +115,7 @@
cooling-min-level = <0>;
cooling-max-level = <7>;
#cooling-cells = <2>; /* min followed by max */
+ capacity-dmips-mhz = <539>;
};
cpu7: cpu@103 {
@@ -121,6 +128,7 @@
cooling-min-level = <0>;
cooling-max-level = <7>;
#cooling-cells = <2>; /* min followed by max */
+ capacity-dmips-mhz = <539>;
};
};
};
The following 'capacity-dmips-mhz' dt property values are used: Cortex-A15: 1024, Cortex-A7: 539 They have been derived from the cpu_efficiency values: Cortex-A15: 3891, Cortex-A7: 2048 by scaling them so that the Cortex-A15s (big cores) use 1024. The cpu_efficiency values were originally derived from the "Big.LITTLE Processing with ARM Cortex™-A15 & Cortex-A7" white paper (http://www.cl.cam.ac.uk/~rdm34/big.LITTLE.pdf). Table 1 lists 1.9x (3891/2048) as the Cortex-A15 vs Cortex-A7 performance ratio for the Dhrystone benchmark. The following platforms are affected once cpu-invariant accounting support is re-connected to the task scheduler: arndale-octa, peach-pi, peach-pit, smdk5420 The patch has been tested on Samsung Chromebook 2 13" (peach-pi, Exynos 5800). $ cat /sys/devices/system/cpu/cpu*/cpu_capacity 1024 1024 1024 1024 389 389 389 389 The Cortex-A15 vs Cortex-A7 performance ratio is 1024/389 = 2.63. The values derived with the 'cpu_efficiency/clock-frequency dt property' solution are: $ cat /sys/devices/system/cpu/cpu*/cpu_capacity 1535 1535 1535 1535 448 448 448 448 The Cortex-A15 vs Cortex-A7 performance ratio is 1535/448 = 3.43. The discrepancy between 2.63 and 3.43 is due to the false assumption when using the 'cpu_efficiency/clock-frequency dt property' solution that the max cpu frequency of the little cpus is 1 GHZ and not 1.3 GHz. The Cortex-A7 cluster runs with a max cpu frequency of 1.3 GHZ whereas the 'clock-frequency' property value is set to 1 GHz. 3.43/1.3 = 2.64 $ cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_max_freq 1800000 1800000 1800000 1800000 1300000 <-- max cpu frequency of the Cortex-A7s (little cores) 1300000 1300000 1300000 Running another benchmark (single-threaded sysbench affine to the individual cpus) with performance cpufreq governor on the Samsung Chromebook 2 13" showed the following numbers: $ for i in `seq 0 7`; do taskset -c $i sysbench --test=cpu --num-threads=1 --max-time=10 run | grep "total number of events:"; done total number of events: 1083 total number of events: 1085 total number of events: 1085 total number of events: 1085 total number of events: 454 total number of events: 454 total number of events: 454 total number of events: 454 The Cortex-A15 vs Cortex-A7 performance ratio is 2.39, i.e. very close to the one derived from the Dhrystone based one of the "Big.LITTLE Processing with ARM Cortex™-A15 & Cortex-A7" white paper (2.63). We don't aim for exact values for the cpu capacity values. Besides the CPI (Cycles Per Instruction), the instruction mix and whether the system runs cpu-bound or memory-bound has an impact on the cpu capacity values derived from these benchmark results. Cc: Rob Herring <robh+dt@kernel.org> Cc: Mark Rutland <mark.rutland@arm.com> Cc: Russell King <linux@armlinux.org.uk> Cc: Kukjin Kim <kgene@kernel.org> Cc: Krzysztof Kozlowski <krzk@kernel.org> Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com> --- arch/arm/boot/dts/exynos5420-cpus.dtsi | 8 ++++++++ 1 file changed, 8 insertions(+) -- 2.11.0