Messages in this thread | | | From | Dietmar Eggemann <> | Subject | [PATCH v2 0/1] arm: remove cpu_efficiency | Date | Thu, 12 Oct 2017 15:00:27 +0100 |
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v1: review results [1]:
Vincent pointed out that there is a superfluous continue statement in parse_dt_topology(). Got rid of it. Krzysztof Kozlowski took the exynos and Simon Horman the renesas related dt bits into their for-next (v4.15) branches.
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For Cortex-A15/A7 arm big.LITTLE systems there are currently two ways to set the cpu capacity.
The first one (commit 06073ee26775 "ARM: 8621/3: parse cpu capacity-dmips-mhz from DT") is based on dt 'cpu capacity-dmips-mhz' bindings and the appropriate dt parsing code in drivers/base/arch_topology.c. It further takes differences in maximum cpu frequency values into consideration, normalizes the maximum cpu capacity to SCHED_CAPACITY_SCALE (1024) and scales all the cpus accordingly.
cpu capacity = (capacity-dmips-mhz * max cpu frequency) / (max capacity-dmips-mhz * max (max cpu frequency)
This solution is shared between arm and arm64 and works for other combinations of big and little cpus (besides Cortex-A15/A7) as well.
The second one (commit 339ca09d7ada "ARM: 7463/1: topology: Update cpu_power according to DT information" is based on the 'struct cpu_efficiency table_efficiency[]' and the dt parsing code in arch/arm/kernel/topology.c. It further requires a clock-frequency property per cpu node, calculates a so called middle frequency for an average cpu in the system which is as close as possible to SCHED_CAPACITY_SCALE (1024) and uses this to compute the cpu capacity values.
cpu capacity = (cpu efficiency * clock frequency) / middle capacity
This solution only works for Cortex-A15/A7 arm big.LITTLE systems.
The aim of this patch is to have only one solution for all arm and arm64 big.LITTLE platforms.
(1) Therefore, it removes the code for the 'cpu_efficiency/ clock-frequency dt property' (second) solution.
(2) Moreover, it will also assure that the highest original cpu capacity (rq->cpu_capacity_orig) in a non-smt system is SCHED_CAPACITY_SCALE (1024).
(3) And finally, another advantage is the dynamic detection of the max cpu frequency which comes with the first solution instead of the static clock-frequency dt property value.
Currently, the arm dt parsing code in parse_dt_topology() checks if the dt uses the capacity-dmips-mhz property. If this is the case it uses the first, otherwise the second solution. This patch removes the code for the second solution from arch/arm/kernel/topology.c.
With the dt related patches for exynos and renesas now in the appropriated for-next branches for v4.15 there are no Cortex-A15/A7 arm big.LITTLE systems left relying on the 'cpu_efficiency/clock-frequency dt property' based solution anymore.
This patch has been tested on TC2 and Samsung Chromebook 2 13" (peach-pi, Exynos 5800).
[1] https://marc.info/?l=linux-kernel&m=150410411807050&w=2
Changes v1->v2:
- Rebase on top of v4.14-rc4 - Remove superfluous continue statement in parse_dt_topology() [01/04] - Remove 'cpu capacity scale management' and 'cpu capacity table' related comments [01/04] - Remove dt related patches [02-04/04]
Dietmar Eggemann (1): arm: topology: remove cpu_efficiency
arch/arm/kernel/topology.c | 132 ++------------------------------------------- 1 file changed, 4 insertions(+), 128 deletions(-)
-- 2.11.0
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