Revert: [Android] Let the raster thread use every core of a chip without little cores - #195838

…out little cores (flutter#195838)

Reverts: [[Android] Let the raster thread use every core of a chip
without little cores](flutter#195071)

Initiated by: @gaaclarke

Reason for reverting: 1) we address the problem where the energy
measurement shows the tradeoff

Original PR Author: @Lopution

Reviewed By: @gaaclarke

The original PR description is provided below:

`CPUSpeedTracker` counts the CPUs with the lowest `cpuinfo_max_freq` as
efficiency cores, and the raster thread is set to the other cores
(`kNotEfficiency`, renamed `kNotLittle` in this PR). On a chip without
little cores, those are full-size cores. On the Snapdragon 8 Elite and 8
Elite Gen 5 (two prime and six performance Oryon cores) the raster
thread only gets the two prime cores. They are mostly idle, so raster
frames start at the cluster's lowest frequency. See flutter#195070 for
measurements.

This change also reads `/sys/devices/system/cpu/cpuN/cpu_capacity`, the
kernel's rating of each CPU, scaled so that the fastest is 1024. When
every CPU has a capacity and none is below half of the fastest, the chip
has no little cores, and `kNotLittle` is every core.

- Why half: little cores rate well below it. Upstream SM8650 device
trees put the Cortex-A520 at about 37% of the X4 at their top
frequencies. The SM8850's performance cores are at 762 of 1024.
- Equal capacities, or a CPU without one, change nothing. A kernel
without capacity data reports 1024 for every CPU.
- Other affinities do not change. `kEfficiency` is still the slowest
group, so background threads stay off the prime cores.
- `kNotEfficiency` is renamed `kNotLittle`, since on these chips it
includes the efficiency cores. Each `CpuAffinity` value's doc says which
cores it covers, and that performance and efficiency there are speed
groups, not the industry's core types.
- Chips with little cores (Snapdragon 8 Gen 1–3, Tensor, Exynos 2400)
should keep the current set. I have only read the capacities of the
SM8850.
- Other chips without little cores also get every core. Examples:
Dimensity 9300/9400 (the slowest group is four Cortex-A720), Snapdragon
8s Gen 4, and Snapdragon 8 Elite Gen 6. On the 8 Elite Gen 6 the six
performance cores report two top frequencies (4.03 and 3.74 GHz), so
today three of them count as efficiency cores. I have not measured these
chips.
- On the Dimensity 9600 Pro (2 × C2-Ultra at 4.55 GHz, 3 × C2-Pro at
4.35 GHz, 3 × C2-Pro at 3.1 GHz), the 3.1 GHz cores should rate near
half, so it may go either way. Either way the raster thread keeps at
least the five cores it gets today.

This keeps the current design and only widens it where the capacities
are clear. A chip whose performance cores rate below half of its prime
cores would still leave the raster thread on the prime cores. The more
general fix would be to stop pinning the raster thread, as Android does
not pin a native app's RenderThread. That needs measurements on the
devices that flutter-team-archive/engine#45673
and flutter#153690 were about, so this change leaves it out.

Tests: three new `CpuAffinity` tests in `fml_unittests`. `NoLittleCores`
fails without this change. I ran the `CpuAffinity` tests against the
changed files in a standalone build with clang++ and g++, not in a full
engine build. On an SM8850 phone, setting the raster threads to every
core from the app (the same result as this change) gave the numbers in
flutter#195070. I have not tested a custom engine build on the device.

Fixes flutter#195070

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responsibilities.
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we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant in-code documentation (doc comments with
`///`).
- [x] If this PR introduces a new feature or capability, I created and
linked a website documentation issue or PR in [flutter/website] (or
verified none is needed).
- [x] I added new tests to check the change I am making, or this PR is
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- [ ] All existing and new tests are passing.

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Roll Flutter from fcfb4f203eae to 934720261be0 (38 revisions)

flutter/flutter@fcfb4f2...9347202

2026-11-03 [email protected] Roll Skia from 5bceaa033999 to c733ad3e37cb (5 revisions) (flutter/flutter#195872)
2026-11-03 [email protected] Roll Skia from 34d2bf479385 to 5bceaa033999 (9 revisions) (flutter/flutter#195864)
2026-11-03 [email protected] fix: prefer pointer events over semantics tap for mouse clicks on web (flutter/flutter#191529)
2026-11-03 [email protected] [VPAT] Expose a semantics text field value while it is not being edited (flutter/flutter#195445)
2026-11-03 [email protected] [Impeller] Make a GL context current before constructing an AiksContext without a surface (flutter/flutter#195629)
2026-11-03 [email protected] [flutter_tools] Eliminate globals.dart from project.dart (flutter/flutter#194066)
2026-11-03 [email protected] [tool] Complete context runner elimination and migrate AppContext usages to ToolContext (flutter/flutter#190797)
2026-11-03 [email protected] [web] Unify font collections between CanvasKit and Skwasm (flutter/flutter#195539)
2026-11-03 [email protected] [Android] Replay predictive back state for retained engines (flutter/flutter#192286)
2026-11-03 [email protected] [vulkan]: Adds depth/stencil synchronization for subpasses (flutter/flutter#195689)
2026-11-03 [email protected] [web] Honor requested upscaling in instantiateImageCodecWithSize and ImageDescriptor.instantiateCodec (flutter/flutter#195836)
2026-11-03 [email protected] Roll Skia from 866b61ca92c9 to 34d2bf479385 (9 revisions) (flutter/flutter#195848)
2026-11-03 [email protected] Roll Fuchsia Test Scripts from xl1LWBuppzu-BnOzV... to B6zarykZp6PKWRueg... (flutter/flutter#195847)
2026-11-03 [email protected] Remove unused ffi (flutter/flutter#195710)
2026-11-02 [email protected] Revert: [Android] Let the raster thread use every core of a chip without little cores (flutter/flutter#195838)
2026-11-02 [email protected] Run 10 impeller iOS benchmarks as one devicelab task (flutter/flutter#195661)
2026-11-02 [email protected] Use named uniforms instead of setFloat in StretchEffect (flutter/flutter#195372)
2026-11-02 [email protected] [flutter_tools] Report when the browser disconnects during a web test run (flutter/flutter#192198)
2026-11-02 [email protected] fix: Resolve memory leak in image_list example (flutter/flutter#189526)
2026-11-02 [email protected] Only run the common local engine configurations in presubmit (flutter/flutter#195688)
2026-11-02 [email protected] Update gcloud_version to version [email protected] (flutter/flutter#195769)
2026-11-02 [email protected] [Impeller] Order the Vulkan copy-texture-to-texture layout transition after the copy (flutter/flutter#195814)
2026-11-02 [email protected] [Impeller] Order the Vulkan ResizeTexture layout transition after its blit (flutter/flutter#195721)
2026-11-02 [email protected] [web] Fix CanvasKit fragment shader uniforms being freed or mutated after recording (flutter/flutter#195718)
2026-11-02 [email protected] Roll Fuchsia Linux SDK from MqypI6RNyVZ_FLUE-... to T_-6-6X1lDMghhAvX... (flutter/flutter#195809)
2026-11-02 [email protected] [Android] Log why Impeller falls back to OpenGLES (flutter/flutter#194764)
2026-11-02 [email protected] Roll Skia from 3f35fb6e591b to 866b61ca92c9 (11 revisions) (flutter/flutter#195802)
2026-11-02 [email protected] Roll Skia from 3f35fb6e591b to 866b61ca92c9 (11 revisions) (flutter/flutter#195802)
2026-11-02 [email protected] Only run the common local engine configurations in presubmit (flutter/flutter#195688)
2026-11-02 [email protected] Balance tool_integration_tests subshards by expected duration (flutter/flutter#195628)
2026-11-02 [email protected] [web_paragraph] Map code units without a cluster to a cluster (flutter/flutter#195384)
2026-11-02 [email protected] [web] Hide synthetic autofill inputs from assistive technology (flutter/flutter#195618)
2026-11-02 [email protected] Roll Packages from 3742a4e to 3f34a6f (8 revisions) (flutter/flutter#195795)
2026-11-02 [email protected] [web] Unskip web tests that pass on CanvasKit and Skwasm: platform_view_test, route_notification_messages_test (flutter/flutter#195605)
2026-11-02 [email protected] Roll Skia from e5ad3868b8db to 3f35fb6e591b (1 revision) (flutter/flutter#195789)
2026-11-02 [email protected] Roll Skia from f5215e74aa16 to e5ad3868b8db (3 revisions) (flutter/flutter#195779)
2026-11-02 [email protected] Roll Skia from e43478a2f9f8 to f5215e74aa16 (1 revision) (flutter/flutter#195776)
2026-11-01 [email protected] Roll Fuchsia Linux SDK from kW0A0xxNkqf38ljm4... to MqypI6RNyVZ_FLUE-... (flutter/flutter#195768)

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