From mboxrd@z Thu Jan 1 00:00:00 1970 From: dietmar.eggemann@arm.com (Dietmar Eggemann) Date: Wed, 30 Aug 2017 15:41:18 +0100 Subject: [PATCH 2/4] arm: dts: exynos: add exynos5420 cpu capacity-dmips-mhz information In-Reply-To: <20170830144120.9312-1-dietmar.eggemann@arm.com> References: <20170830144120.9312-1-dietmar.eggemann@arm.com> Message-ID: <20170830144120.9312-3-dietmar.eggemann@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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 Cc: Mark Rutland Cc: Russell King Cc: Kukjin Kim Cc: Krzysztof Kozlowski Signed-off-by: Dietmar Eggemann --- arch/arm/boot/dts/exynos5420-cpus.dtsi | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/arch/arm/boot/dts/exynos5420-cpus.dtsi b/arch/arm/boot/dts/exynos5420-cpus.dtsi index 5c052d7ff554..d7d703aa1699 100644 --- a/arch/arm/boot/dts/exynos5420-cpus.dtsi +++ b/arch/arm/boot/dts/exynos5420-cpus.dtsi @@ -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 at 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 at 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 at 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 at 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 at 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 at 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 at 103 { @@ -121,6 +128,7 @@ cooling-min-level = <0>; cooling-max-level = <7>; #cooling-cells = <2>; /* min followed by max */ + capacity-dmips-mhz = <539>; }; }; }; -- 2.11.0