ANDROID: Move AutoFDO profile to gki/aarch64/afdo

Relocate AutoFDO profiles from toolchain/pgo-profiles/kernel
to common/gki/aarch64/afdo for better organization within
each release branch.

Also update the AutoFDO profile for kernel version 6.12.18.

Bug: 404538865
Test: build
Change-Id: Idf167e5393339fe3ce79a946ec381725b093c3b9
Signed-off-by: Yabin Cui <yabinc@google.com>

BUILD.bazel

@@ -4,7 +4,6 @@
 load("@bazel_skylib//lib:paths.bzl", "paths")
 load("@bazel_skylib//rules:common_settings.bzl", "string_flag")
 load("@bazel_skylib//rules:write_file.bzl", "write_file")
-load("@kernel_toolchain_info//:dict.bzl", "BRANCH")
 load("@rules_cc//cc:defs.bzl", "cc_library")
 load("@rules_pkg//pkg:install.bzl", "pkg_install")
 load("@rules_pkg//pkg:mappings.bzl", "pkg_filegroup", "pkg_files", "strip_prefix")
@@ -328,7 +327,7 @@ common_kernel(
     additional_kmi_symbol_lists = [":aarch64_additional_kmi_symbol_lists"],
     arch = "arm64",
     build_gki_artifacts = True,
-    clang_autofdo_profile = "//toolchain/pgo-profiles/kernel:aarch64/" + BRANCH + "/kernel.afdo",
+    clang_autofdo_profile = ":gki/aarch64/afdo/kernel.afdo",
     ddk_headers_archive = ":kernel_aarch64_ddk_headers_archive",
     ddk_module_headers = [":all_headers_aarch64"],
     defconfig = "arch/arm64/configs/gki_defconfig",

gki/README.md

@@ -13,7 +13,8 @@ gki
 |   |   +-- ...
 |   |-- protected_exports
 |   |-- abi.stg
-|   +-- abi.stg.allowed_breaks
+|   |-- abi.stg.allowed_breaks
+|   +-- afdo
 +-- ...
 ```
 
@@ -35,3 +36,4 @@ architecture. Within each such subdirectory:
    * e.g. `tools/bazel run //common:kernel_aarch64_abi_update`
 * `abi.stg.allowed_breaks` - a list of allowed ABI differences
    * for use by Gerrit ABI monitoring
+* `afdo` - [AutoFDO profile for building kernel for the architecture](aarch64/afdo/README.md)

gki/aarch64/afdo/README.md

@@ -0,0 +1,51 @@
+
+# AutoFDO profiles for Android common kernels
+
+This directory contains AutoFDO profiles for Android common kernels. These profiles can be used to
+optimize kernel builds for specific architectures and kernel versions.
+
+## kernel.afdo
+
+kernel.afdo is an AArch64 kernel profile collected on kernel version 6.12.18 (
+SHA fbd1fef4d7283d210845f8609599efd53c0905a4, build server ID 13287522) using Pixel 6.
+
+### Performance improvements
+
+| Benchmark             | Improvement |
+| --------------------- | ----------- |
+| Boot time             | 2.6%        |
+| Cold App launch time  | 3.7%        |
+| Binder-rpc            | 9.4%        |
+| Binder-addints        | 31.9%       |
+| Hwbinder              | 16.5%       |
+| Bionic (syscall_mmap) | 7.1%        |
+| Bionic (pthread)      | 3.3%        |
+| Bionic (stdio)        | 3.7%        |
+| Bionic (all)          | 3.4%        |
+
+Benchmark results were tested on Pixel 6.
+
+To test a kernel prebuilt with the AutoFDO profile, navigate to [Android build server](
+https://ci.android.com/builds/branches/aosp_kernel-common-android16-6.12/grid) and download
+the kernel prebuilts under the `kernel_aarch64_autofdo` target.
+
+## Steps to reproduce the profile
+
+A kernel profile is generated by running app crawling and app launching for top 100 apps from Google
+Play Store. While running, we collect ETM data for the kernel, which records executed instruction
+stream. Finally, we merge and convert ETM data to one AutoFDO profile.
+
+1. Build a kernel image and flash it on an Android device
+  * The source code and test device used to generate each profile are described above.
+  * We use a Pixel device. But using other real devices should get a similar profile.
+
+2. Run app crawling and app launching for top 100 apps
+  * Add a gmail account on the test device. Because app crawler can use the account to automatically
+    login some of the apps.
+  * We run [App Crawler](https://developer.android.com/studio/test/other-testing-tools/app-crawler)
+    for one app for 3 minutes, and run it twice.
+  * We run app launching for one app for 3 seconds, and run it 15 times. After each running, the
+    app is killed and cache is cleared. So we get profile for cold app startups.
+
+3. Record ETM data while running app crawling and app launching.
+  * We use cmdline `simpleperf record -e cs-etm:k -a` to [record ETM data for the kernel](https://android.googlesource.com/platform/system/extras/+/master/simpleperf/doc/collect_etm_data_for_autofdo.md).