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author | Dietmar Eggemann <dietmar.eggemann@arm.com> | 2017-08-30 15:41:18 +0100 |
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committer | Krzysztof Kozlowski <krzk@kernel.org> | 2017-09-17 09:35:03 +0200 |
commit | 45bfc2a3f762b5d5282d5ec2dd96b1fe3a9329ca (patch) | |
tree | a70cac7b440593dd9a648a9cbbbe6baf59befbeb /arch/arm/boot/dts/exynos5420-cpus.dtsi | |
parent | e740731dae9470f7fb86efa643ec881a66d4e4c0 (diff) | |
download | linux-45bfc2a3f762b5d5282d5ec2dd96b1fe3a9329ca.tar.bz2 |
ARM: dts: exynos: add exynos5420 cpu capacity-dmips-mhz information
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>
Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Diffstat (limited to 'arch/arm/boot/dts/exynos5420-cpus.dtsi')
-rw-r--r-- | arch/arm/boot/dts/exynos5420-cpus.dtsi | 8 |
1 files changed, 8 insertions, 0 deletions
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@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>; }; }; }; |