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Groups > linux.kernel > #1723411
| From | Dietmar Eggemann <dietmar.eggemann@arm.com> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | [PATCH 2/4] arm: dts: exynos: add exynos5420 cpu capacity-dmips-mhz information |
| Date | 2017-08-30 16:50 +0200 |
| Message-ID | <ukctB-16f-51@gated-at.bofh.it> (permalink) |
| References | <ukctz-16f-3@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
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(+)
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>;
};
};
};
--
2.11.0
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[PATCH 0/4] arm: remove cpu_efficiency Dietmar Eggemann <dietmar.eggemann@arm.com> - 2017-08-30 16:50 +0200
[PATCH 2/4] arm: dts: exynos: add exynos5420 cpu capacity-dmips-mhz information Dietmar Eggemann <dietmar.eggemann@arm.com> - 2017-08-30 16:50 +0200
Re: [PATCH 2/4] arm: dts: exynos: add exynos5420 cpu capacity-dmips-mhz information Krzysztof Kozlowski <krzk@kernel.org> - 2017-08-30 22:30 +0200
Re: [PATCH 2/4] arm: dts: exynos: add exynos5420 cpu capacity-dmips-mhz information Dietmar Eggemann <dietmar.eggemann@arm.com> - 2017-08-31 12:40 +0200
Re: [PATCH 2/4] arm: dts: exynos: add exynos5420 cpu capacity-dmips-mhz information Krzysztof Kozlowski <krzk@kernel.org> - 2017-09-03 22:00 +0200
Re: [PATCH 2/4] arm: dts: exynos: add exynos5420 cpu capacity-dmips-mhz information Dietmar Eggemann <dietmar.eggemann@arm.com> - 2017-09-06 13:50 +0200
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