Message-ID: <20241002233409.2857999-7-xur@google.com>
Date: Wed,  2 Oct 2024 16:34:05 -0700
From: Rong Xu <xur@...gle.com>
To: Rong Xu <xur@...gle.com>, Han Shen <shenhan@...gle.com>, 
	Sriraman Tallam <tmsriram@...gle.com>, David Li <davidxl@...gle.com>, 
	Krzysztof Pszeniczny <kpszeniczny@...gle.com>, Alice Ryhl <aliceryhl@...gle.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Arnd Bergmann <arnd@...db.de>, 
	Bill Wendling <morbo@...gle.com>, Borislav Petkov <bp@...en8.de>, Breno Leitao <leitao@...ian.org>, 
	Brian Gerst <brgerst@...il.com>, Dave Hansen <dave.hansen@...ux.intel.com>, 
	Heiko Carstens <hca@...ux.ibm.com>, "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>, 
	Jann Horn <jannh@...gle.com>, Jonathan Corbet <corbet@....net>, Josh Poimboeuf <jpoimboe@...nel.org>, 
	Juergen Gross <jgross@...e.com>, Justin Stitt <justinstitt@...gle.com>, Kees Cook <kees@...nel.org>, 
	linux-arch@...r.kernel.org, linux-doc@...r.kernel.org, 
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org, 
	llvm@...ts.linux.dev, Masahiro Yamada <masahiroy@...nel.org>, 
	"Mike Rapoport (IBM)" <rppt@...nel.org>, Nathan Chancellor <nathan@...nel.org>, 
	Nick Desaulniers <ndesaulniers@...gle.com>, Nicolas Schier <nicolas@...sle.eu>, 
	"Paul E. McKenney" <paulmck@...nel.org>, Peter Zijlstra <peterz@...radead.org>, 
	Samuel Holland <samuel.holland@...ive.com>, Thomas Gleixner <tglx@...utronix.de>, 
	Wei Yang <richard.weiyang@...il.com>, workflows@...r.kernel.org, x86@...nel.org, 
	"Xin Li (Intel)" <xin@...or.com>
Cc: Stephane Eranian <eranian@...gle.com>
Subject: [PATCH v2 6/6] Add Propeller configuration for kernel build.

Add the build support for using Clang's Propeller optimizer. Like
AutoFDO, Propeller uses hardware sampling to gather information
about the frequency of execution of different code paths within a
binary. This information is then used to guide the compiler's
optimization decisions, resulting in a more efficient binary.

The support requires a Clang compiler LLVM 19 or later, and the
create_llvm_prof tool
(https://github.com/google/autofdo/releases/tag/v0.30.1). This
submission is limited to x86 platforms that support PMU features
like LBR on Intel machines and AMD Zen3 BRS.

For Arm, we plan to send patches for SPE-based Propeller when
AutoFDO for Arm is ready.

Here is an example workflow for building an AutoFDO+Propeller
optimized kernel:

1) Build the kernel on the HOST machine, with AutoFDO and Propeller
   build config
      CONFIG_AUTOFDO_CLANG=y
      CONFIG_PROPELLER_CLANG=y
   then
      $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<autofdo_profile>

“<autofdo_profile>” is the profile collected when doing a non-Propeller
AutoFDO build. This step builds a kernel that has the same optimization
level as AutoFDO, plus a metadata section that records basic block
information. This kernel image runs as fast as an AutoFDO optimized
kernel.

2) Install the kernel on test/production machines.

3) Run the load tests. The '-c' option in perf specifies the sample
   event period. We suggest using a suitable prime number,
   like 500009, for this purpose.
   For Intel platforms:
      $ perf record -e BR_INST_RETIRED.NEAR_TAKEN:k -a -N -b -c <count> \
        -o <perf_file> -- <loadtest>
   For AMD platforms:
      The supported system are: Zen3 with BRS, or Zen4 with amd_lbr_v2
      # To see if Zen3 support LBR:
      $ cat proc/cpuinfo | grep " brs"
      # To see if Zen4 support LBR:
      $ cat proc/cpuinfo | grep amd_lbr_v2
      # If the result is yes, then collect the profile using:
      $ perf record --pfm-events RETIRED_TAKEN_BRANCH_INSTRUCTIONS:k -a \
        -N -b -c <count> -o <perf_file> -- <loadtest>

4) (Optional) Download the raw perf file to the HOST machine.

5) Generate Propeller profile:
   $ create_llvm_prof --binary=<vmlinux> --profile=<perf_file> \
     --format=propeller --propeller_output_module_name \
     --out=<propeller_profile_prefix>_cc_profile.txt \
     --propeller_symorder=<propeller_profile_prefix>_ld_profile.txt

   “create_llvm_prof” is the profile conversion tool, and a prebuilt
   binary for linux can be found on
   https://github.com/google/autofdo/releases/tag/v0.30.1 (can also build
   from source).

   "<propeller_profile_prefix>" can be something like
   "/home/user/dir/any_string".

   This command generates a pair of Propeller profiles:
   "<propeller_profile_prefix>_cc_profile.txt" and
   "<propeller_profile_prefix>_ld_profile.txt".

6) Rebuild the kernel using the AutoFDO and Propeller profile files.
      CONFIG_AUTOFDO_CLANG=y
      CONFIG_PROPELLER_CLANG=y
   and
      $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<autofdo_profile> \
        CLANG_PROPELLER_PROFILE_PREFIX=<propeller_profile_prefix>

Co-developed-by: Han Shen <shenhan@...gle.com>
Signed-off-by: Han Shen <shenhan@...gle.com>
Signed-off-by: Rong Xu <xur@...gle.com>
Suggested-by: Sriraman Tallam <tmsriram@...gle.com>
Suggested-by: Krzysztof Pszeniczny <kpszeniczny@...gle.com>
Suggested-by: Nick Desaulniers <ndesaulniers@...gle.com>
Suggested-by: Stephane Eranian <eranian@...gle.com>
---
 Documentation/dev-tools/index.rst     |   1 +
 Documentation/dev-tools/propeller.rst | 188 ++++++++++++++++++++++++++
 MAINTAINERS                           |   7 +
 Makefile                              |   1 +
 arch/Kconfig                          |  22 +++
 arch/x86/Kconfig                      |   1 +
 arch/x86/kernel/vmlinux.lds.S         |   4 +
 include/asm-generic/vmlinux.lds.h     |  10 +-
 scripts/Makefile.lib                  |  10 ++
 scripts/Makefile.propeller            |  28 ++++
 tools/objtool/check.c                 |   1 +
 11 files changed, 268 insertions(+), 5 deletions(-)
 create mode 100644 Documentation/dev-tools/propeller.rst
 create mode 100644 scripts/Makefile.propeller

diff --git a/Documentation/dev-tools/index.rst b/Documentation/dev-tools/index.rst
index 6945644f7008..3c0ac08b2709 100644
--- a/Documentation/dev-tools/index.rst
+++ b/Documentation/dev-tools/index.rst
@@ -35,6 +35,7 @@ Documentation/dev-tools/testing-overview.rst
    checkuapi
    gpio-sloppy-logic-analyzer
    autofdo
+   propeller
 
 
 .. only::  subproject and html
diff --git a/Documentation/dev-tools/propeller.rst b/Documentation/dev-tools/propeller.rst
new file mode 100644
index 000000000000..15ef0e6d973e
--- /dev/null
+++ b/Documentation/dev-tools/propeller.rst
@@ -0,0 +1,188 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=====================================
+Using Propeller with the Linux kernel
+=====================================
+
+This enables Propeller build support for the kernel when using Clang
+compiler. Propeller is a profile-guided optimization (PGO) method used
+to optimize binary executables. Like AutoFDO, it utilizes hardware
+sampling to gather information about the frequency of execution of
+different code paths within a binary. Unlike AutoFDO, this information
+is then used right before linking phase to optimize (among others)
+block layout within and across functions.
+
+A few important notes about adopting Propeller optimization:
+
+#. Although it can be used as a standalone optimization step, it is
+   strongly recommended to apply Propeller on top of AutoFDO,
+   AutoFDO+ThinLTO or Instrument FDO. The rest of this document
+   assumes this paradigm.
+
+#. Propeller uses another round of profiling on top of
+   AutoFDO/AutoFDO+ThinLTO/iFDO. The whole build process involves
+   "build-afdo - train-afdo - build-propeller - train-propeller -
+   build-optimized".
+
+#. Propeller requires LLVM 19 release or later for Clang/Clang++
+   and the linker(ld.lld).
+
+#. In addition to LLVM toolchain, Propeller requires a profiling
+   conversion tool: https://github.com/google/autofdo with a release
+   after v0.30.1: https://github.com/google/autofdo/releases/tag/v0.30.1.
+
+The Propeller optimization process involves the following steps:
+
+#. Initial building: Build the AutoFDO or AutoFDO+ThinLTO binary as
+   you would normally do, but with a set of compile-time / link-time
+   flags, so that a special metadata section is created within the
+   kernel binary. The special section is only intend to be used by the
+   profiling tool, it is not part of the runtime image, nor does it
+   change kernel run time text sections.
+
+#. Profiling: The above kernel is then run with a representative
+   workload to gather execution frequency data. This data is collected
+   using hardware sampling, via perf. Propeller is most effective on
+   platforms supporting advanced PMU features like LBR on Intel
+   machines. This step is the same as profiling the kernel for AutoFDO
+   (the exact perf parameters can be different).
+
+#. Propeller profile generation: Perf output file is converted to a
+   pair of Propeller profiles via an offline tool.
+
+#. Optimized build: Build the AutoFDO or AutoFDO+ThinLTO optimized
+   binary as you would normally do, but with a compile-time /
+   link-time flag to pick up the Propeller compile time and link time
+   profiles. This build step uses 3 profiles - the AutoFDO profile,
+   the Propeller compile-time profile and the Propeller link-time
+   profile.
+
+#. Deployment: The optimized kernel binary is deployed and used
+   in production environments, providing improved performance
+   and reduced latency.
+
+Preparation
+===========
+
+Configure the kernel with:
+
+   .. code-block:: make
+
+      CONFIG_AUTOFDO_CLANG=y
+      CONFIG_PROPELLER_CLANG=y
+
+Customization
+=============
+
+You can enable or disable Propeller build for individual file and
+directories by adding a line similar to the following to the
+respective kernel Makefile:
+
+- For enabling a single file (e.g. foo.o)
+
+     .. code-block:: make
+
+        PROPELLER_PROFILE_foo.o := y
+
+- For enabling all files in one directory
+
+     .. code-block:: make
+
+        PROPELLER_PROFILE := y
+
+- For disabling one file
+
+     .. code-block:: make
+
+        PROPELLER_PROFILE_foo.o := n
+
+- For disabling all files in one directory
+
+     .. code-block:: make
+
+        PROPELLER__PROFILE := n
+
+
+Workflow
+========
+
+Here is an example workflow for building an AutoFDO+Propeller kernel:
+
+1) Assuming an AutoFDO profile is already collected following
+   instructions in the AutoFDO document, build the kernel on the HOST
+   machine, with AutoFDO and Propeller build configs:
+
+      .. code-block:: make
+
+         CONFIG_AUTOFDO_CLANG=y
+         CONFIG_PROPELLER_CLANG=y
+
+   and
+
+      .. code-block:: sh
+
+         $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<autofdo-profile-name>
+
+2) Install the kernel on the TEST machine.
+
+3) Run the load tests. The '-c' option in perf specifies the sample
+   event period. We suggest using a suitable prime number, like 500009,
+   for this purpose.
+
+   - For Intel platforms:
+
+      .. code-block:: sh
+
+         $ perf record -e BR_INST_RETIRED.NEAR_TAKEN:k -a -N -b -c \
+           <count> -o <perf_file> -- <loadtest>
+
+   - For AMD platforms:
+
+      .. code-block:: sh
+
+         $ perf record --pfm-event RETIRED_TAKEN_BRANCH_INSTRUCTIONS:k \
+           -a -N -b -c <count> -o <perf_file> -- <loadtest>
+
+   Note you can repeat the above steps to collect multiple <perf_file>s.
+
+4) (Optional) Download the raw perf file(s) to the HOST machine.
+
+5) Use the create_llvm_prof tool (https://github.com/google/autofdo) to Generate Propeller profile.
+
+      .. code-block:: sh
+
+         $ create_llvm_prof --binary=<vmlinux> --profile=<perf_file> \
+                            --format=propeller --propeller_output_module_name \
+                            --out=<propeller_profile_prefix>_cc_profile.txt \
+                            --propeller_symorder=<propeller_profile_prefix>_ld_profile.txt
+
+   "<propeller_profile_prefix>" can be something like
+   "/home/user/dir/any_string".
+
+   This command generates a pair of Propeller profiles:
+   "<propeller_profile_prefix>_cc_profile.txt" and
+   "<propeller_profile_prefix>_ld_profile.txt".
+
+   If there are more than 1 perf_file collected in the previous step,
+   you can create a temp list file "<perf_file_list>" with each line
+   containing one perf file name and run:
+
+      .. code-block:: sh
+
+         $ create_llvm_prof --binary=<vmlinux> --profile=@<perf_file_list> \
+                            --format=propeller --propeller_output_module_name \
+                            --out=<propeller_profile_prefix>_cc_profile.txt \
+                            --propeller_symorder=<propeller_profile_prefix>_ld_profile.txt
+
+6) Rebuild the kernel using the AutoFDO and Propeller profiles.
+
+      .. code-block:: make
+
+         CONFIG_AUTOFDO_CLANG=y
+         CONFIG_PROPELLER_CLANG=y
+
+   and
+
+      .. code-block:: sh
+
+         $ make LLVM=1 CLANG_AUTOFDO_PROFILE=<profile_file> CLANG_PROPELLER_PROFILE_PREFIX=<propeller_profile_prefix>
diff --git a/MAINTAINERS b/MAINTAINERS
index 62b798c20128..022b8d233558 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -18556,6 +18556,13 @@ S:	Maintained
 F:	include/linux/psi*
 F:	kernel/sched/psi.c
 
+PROPELLER BUILD
+M:	Rong Xu <xur@...gle.com>
+M:	Han Shen <shenhan@...gle.com>
+S:	Supported
+F:	Documentation/dev-tools/propeller.rst
+F:	scripts/Makefile.propeller
+
 PRINTK
 M:	Petr Mladek <pmladek@...e.com>
 R:	Steven Rostedt <rostedt@...dmis.org>
diff --git a/Makefile b/Makefile
index 55d19c81b382..0fa6d35602a4 100644
--- a/Makefile
+++ b/Makefile
@@ -1019,6 +1019,7 @@ include-$(CONFIG_UBSAN)		+= scripts/Makefile.ubsan
 include-$(CONFIG_KCOV)		+= scripts/Makefile.kcov
 include-$(CONFIG_RANDSTRUCT)	+= scripts/Makefile.randstruct
 include-$(CONFIG_AUTOFDO_CLANG)	+= scripts/Makefile.autofdo
+include-$(CONFIG_PROPELLER_CLANG)	+= scripts/Makefile.propeller
 include-$(CONFIG_GCC_PLUGINS)	+= scripts/Makefile.gcc-plugins
 
 include $(addprefix $(srctree)/, $(include-y))
diff --git a/arch/Kconfig b/arch/Kconfig
index 106d09fc42ce..5aacd9c8a0d2 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -831,6 +831,28 @@ config AUTOFDO_CLANG
 
 	  If unsure, say N.
 
+config ARCH_SUPPORTS_PROPELLER_CLANG
+	bool
+
+config PROPELLER_CLANG
+	bool "Enable Clang's Propeller build"
+	depends on ARCH_SUPPORTS_PROPELLER_CLANG
+	depends on AUTOFDO_CLANG
+	depends on CC_IS_CLANG && CLANG_VERSION >= 190000
+	help
+	  This option enables Clang’s Propeller build which
+	  is on top of AutoFDO build. When the Propeller profiles
+	  is specified in variable CLANG_PROPELLER_PROFILE_PREFIX
+	  during the build process, Clang uses the profiles to
+	  optimize the kernel.
+
+	  If no profile is specified, Proepller options are
+	  still passed to Clang to facilitate the collection
+	  of perf data for creating the Propeller profiles in
+	  subsequent builds.
+
+	  If unsure, say N.
+
 config ARCH_SUPPORTS_CFI_CLANG
 	bool
 	help
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 503a0268155a..da47164bfddc 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -127,6 +127,7 @@ config X86
 	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_CMPXCHG64
 	select ARCH_USE_MEMTEST
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 6726be89b7a6..7ecc21c569be 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -442,6 +442,10 @@ SECTIONS
 
 	STABS_DEBUG
 	DWARF_DEBUG
+#ifdef CONFIG_PROPELLER_CLANG
+	.llvm_bb_addr_map : { *(.llvm_bb_addr_map) }
+#endif
+
 	ELF_DETAILS
 
 	DISCARDS
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 20e46c0917db..5986dd4cfb14 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -95,14 +95,14 @@
  * With LTO_CLANG, the linker also splits sections by default, so we need
  * these macros to combine the sections during the final link.
  *
- * With LTO_CLANG, the linker also splits sections by default, so we need
- * these macros to combine the sections during the final link.
+ * CONFIG_AUTOFD_CLANG and CONFIG_PROPELLER_CLANG will also split text sections
+ * and cluster them in the linking time.
  *
  * RODATA_MAIN is not used because existing code already defines .rodata.x
  * sections to be brought in with rodata.
  */
 #if defined(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION) || defined(CONFIG_LTO_CLANG) || \
-defined(CONFIG_AUTOFDO_CLANG)
+defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG)
 #define TEXT_MAIN .text .text.[0-9a-zA-Z_]*
 #else
 #define TEXT_MAIN .text
@@ -556,7 +556,7 @@ defined(CONFIG_AUTOFDO_CLANG)
 		__cpuidle_text_end = .;					\
 		__noinstr_text_end = .;
 
-#ifdef CONFIG_AUTOFDO_CLANG
+#if defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG)
 #define TEXT_HOT							\
 		__hot_text_start = .;					\
 		*(.text.hot .text.hot.*)				\
@@ -584,7 +584,7 @@ defined(CONFIG_AUTOFDO_CLANG)
  * first when in these builds.
  */
 #if defined(CONFIG_LD_DEAD_CODE_DATA_ELIMINATION) || defined(CONFIG_LTO_CLANG) || \
-defined(CONFIG_AUTOFDO_CLANG)
+defined(CONFIG_AUTOFDO_CLANG) || defined(CONFIG_PROPELLER_CLANG)
 #define TEXT_TEXT							\
 		ALIGN_FUNCTION();					\
 		*(.text.asan.* .text.tsan.*)				\
diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
index e85d6ac31bd9..60354c476956 100644
--- a/scripts/Makefile.lib
+++ b/scripts/Makefile.lib
@@ -201,6 +201,16 @@ _c_flags += $(if $(patsubst n%,, \
 	$(CFLAGS_AUTOFDO_CLANG))
 endif
 
+#
+# Enable Clang's Propeller build flags for a file or directory depending on
+# variables AUTOFDO_PROPELLER_obj.o and PROPELLER_PROFILE.
+#
+ifeq ($(CONFIG_PROPELLER_CLANG),y)
+_c_flags += $(if $(patsubst n%,, \
+	$(AUTOFDO_PROFILE_$(target-stem).o)$(AUTOFDO_PROFILE)$(PROPELLER_PROFILE))$(is-kernel-object), \
+	$(CFLAGS_PROPELLER_CLANG))
+endif
+
 # $(src) for including checkin headers from generated source files
 # $(obj) for including generated headers from checkin source files
 ifeq ($(KBUILD_EXTMOD),)
diff --git a/scripts/Makefile.propeller b/scripts/Makefile.propeller
new file mode 100644
index 000000000000..344190717e47
--- /dev/null
+++ b/scripts/Makefile.propeller
@@ -0,0 +1,28 @@
+# SPDX-License-Identifier: GPL-2.0
+
+# Enable available and selected Clang Propeller features.
+ifdef CLANG_PROPELLER_PROFILE_PREFIX
+  CFLAGS_PROPELLER_CLANG := -fbasic-block-sections=list=$(CLANG_PROPELLER_PROFILE_PREFIX)_cc_profile.txt -ffunction-sections
+  KBUILD_LDFLAGS += --symbol-ordering-file=$(CLANG_PROPELLER_PROFILE_PREFIX)_ld_profile.txt --no-warn-symbol-ordering
+else
+  CFLAGS_PROPELLER_CLANG := -fbasic-block-sections=labels
+endif
+
+# Propeller requires debug information to embed module names in the profiles.
+# If CONFIG_DEBUG_INFO is not enabled, set -gmlt option. Skip this for AutoFDO,
+# as the option should already be set.
+ifndef CONFIG_DEBUG_INFO
+  ifndef CONFIG_AUTOFDO_CLANG
+    CFLAGS_PROPELLER_CLANG += -gmlt
+  endif
+endif
+
+ifdef CONFIG_LTO_CLANG_THIN
+  ifdef CLANG_PROPELLER_PROFILE_PREFIX
+    KBUILD_LDFLAGS += --lto-basic-block-sections=$(CLANG_PROPELLER_PROFILE_PREFIX)_cc_profile.txt
+  else
+    KBUILD_LDFLAGS += --lto-basic-block-sections=labels
+  endif
+endif
+
+export CFLAGS_PROPELLER_CLANG
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 4c5229991e1e..05a0fb4a3d1a 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -4558,6 +4558,7 @@ static int validate_ibt(struct objtool_file *file)
 		    !strcmp(sec->name, "__mcount_loc")			||
 		    !strcmp(sec->name, ".kcfi_traps")			||
 		    !strcmp(sec->name, ".llvm.call-graph-profile")	||
+		    !strcmp(sec->name, ".llvm_bb_addr_map")		||
 		    strstr(sec->name, "__patchable_function_entries"))
 			continue;
 
-- 
2.46.1.824.gd892dcdcdd-goog

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