Subject: [PATCH v4 1/2] kconfig: Remove the architecture specific config for AutoFDO

From: [email-masked]
Date: Thu, 4 Jun 2026 12:56:07 -0700

From: Rong Xu <[email-masked]>

The CONFIG_AUTOFDO_CLANG option currently depends on
ARCH_SUPPORTS_AUTOFDO_CLANG, but this dependency seems unnecessary.

Remove ARCH_SUPPORTS_AUTOFDO_CLANG and allow users to control AutoFDO
builds solely through CONFIG_AUTOFDO_CLANG. This simplifies the kconfig
and avoids potential confusion.

Expand the AutoFDO documentation to include instructions for arm64.

Contributor acknowledgments:
  * SPE instructions: Daniel Hoekwater <[email-masked]>
  * ETM instructions: Yabin Cui <[email-masked]>

Signed-off-by: Rong Xu <[email-masked]>
Suggested-by: Will Deacon <[email-masked]>
Tested-by: Yabin Cui <[email-masked]>
Reviewed-by: Kees Cook <[email-masked]>
---
 Documentation/dev-tools/autofdo.rst | 41 +++++++++++++++++++++++++++++
 arch/Kconfig                        |  4 ---
 arch/x86/Kconfig                    |  1 -
 3 files changed, 41 insertions(+), 5 deletions(-)

diff --git a/Documentation/dev-tools/autofdo.rst b/Documentation/dev-tools/autofdo.rst
index bcf06e7d6ffa..ae03c4dfedc1 100644
--- a/Documentation/dev-tools/autofdo.rst
+++ b/Documentation/dev-tools/autofdo.rst
@@ -61,6 +61,9 @@ process consists of the following steps:
    the AutoFDO profile via offline tools.
 
 The support requires a Clang compiler LLVM 17 or later.
+Current supported architectures include x86/x86_64 (via LBR) and
+arm64 (via SPE or ETM).
+
 
 Preparation
 ===========
@@ -141,6 +144,35 @@ Here is an example workflow for AutoFDO kernel:
 
       $ perf record --pfm-events RETIRED_TAKEN_BRANCH_INSTRUCTIONS:k -a -N -b -c <count> -o <perf_file> -- <loadtest>
 
+   - For arm64 with SPE:
+
+     There are a few kernel features that must be enabled to collect SPE profiles on Arm.
+     Below is a list of the required features:
+
+      - CONFIG_ARM_SPE_PMU=y
+      - CONFIG_PID_IN_CONTEXTIDR=y
+      - kpti=off
+
+     Use the following command to generate SPE perf data file::
+
+      $ perf record -e ' arm_spe_0/branch_filter=1,load_filter=0,store_filter=0/'  -a -c <count> -N --no-switch-events -o <perf_file> -- <loadtest>
+
+   - For arm64 with ETM trace:
+
+     Follow the instructions in `Linaro OpenCSD document
+     <https://github.com/Linaro/OpenCSD/blob/master/decoder/tests/auto-fdo/autofdo.md>`_
+     to record ETM traces for AutoFDO::
+
+      $ perf record -e cs_etm/@tmc_etr0/k -a -o <etm_perf_file> -- <loadtest>
+      $ perf inject -i <etm_perf_file> -o <perf_file> --itrace=i500009il
+
+     For ARM platforms running Android, follow the instructions in `Android simpleperf
+     document <https://android.googlesource.com/kernel/common/+/refs/heads/android-mainline/gki/aarch64/afdo>`_
+     to record ETM traces for AutoFDO::
+
+      $ simpleperf record -e cs-etm:k -a -o <etm_perf_file> -- <loadtest>
+      $ simpleperf inject -i <etm_perf_file> -o <text_perf_file> --symdir <vmlinux_dir>
+
 4) (Optional) Download the raw perf file to the host machine.
 
 5) To generate an AutoFDO profile, two offline tools are available:
@@ -162,6 +194,15 @@ Here is an example workflow for AutoFDO kernel:
 
       $ llvm-profdata merge -o <profile_file> <profile_1> <profile_2> ... <profile_n>
 
+   For arm64 SPE, use the following command::
+
+      $ create_llvm_prof --binary=<vmlinux> --profile=<perf_file> --profiler=perf_spe --format=extbinary --out=<profile_file>
+
+   For arm64 ETM, use the following command::
+
+      $ create_llvm_prof --binary=<vmlinux> --profile=<text_perf_file> --profiler=text -format=extbinary -out=<profile_file>
+
+
 6) Rebuild the kernel using the AutoFDO profile file with the same config as step 1,
    (Note CONFIG_AUTOFDO_CLANG needs to be enabled)::
 
diff --git a/arch/Kconfig b/arch/Kconfig
index 0848932d1c8e..5e878924939a 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -879,12 +879,8 @@ config LTO_CLANG_THIN_DIST
 	  module-specific compiler options, and simplifies debugging.
 endchoice
 
-config ARCH_SUPPORTS_AUTOFDO_CLANG
-	bool
-
 config AUTOFDO_CLANG
 	bool "Enable Clang's AutoFDO build (EXPERIMENTAL)"
-	depends on ARCH_SUPPORTS_AUTOFDO_CLANG
 	depends on CC_IS_CLANG
 	help
 	  This option enables Clang’s AutoFDO build. When
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index f3f7cb01d69d..10bf3984102e 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -130,7 +130,6 @@ config X86
 	select ARCH_SUPPORTS_LTO_CLANG
 	select ARCH_SUPPORTS_LTO_CLANG_THIN
 	select ARCH_SUPPORTS_RT
-	select ARCH_SUPPORTS_AUTOFDO_CLANG
 	select ARCH_SUPPORTS_PROPELLER_CLANG    if X86_64
 	select ARCH_USE_BUILTIN_BSWAP
 	select ARCH_USE_CMPXCHG_LOCKREF		if X86_CX8
-- 
2.54.0.1032.g2f8565e1d1-goog