Re: [PATCH v5] pgo: add clang's Profile Guided Optimization infrastructure
From: Bill Wendling
Date: Thu Jan 21 2021 - 03:36:38 EST
On Wed, Jan 20, 2021 at 4:51 PM Nick Desaulniers
<ndesaulniers@xxxxxxxxxx> wrote:
>
> Thanks Bill, mostly questions below. Patch looks good to me modulo
> disabling profiling for one crypto TU, mixing style of pre/post
> increment, and some comments around locking. With those addressed,
> I'm hoping akpm@ would consider picking this up.
>
> On Sat, Jan 16, 2021 at 1:44 AM Bill Wendling <morbo@xxxxxxxxxx> wrote:
> >
> > From: Sami Tolvanen <samitolvanen@xxxxxxxxxx>
> >
> > Enable the use of clang's Profile-Guided Optimization[1]. To generate a
> > profile, the kernel is instrumented with PGO counters, a representative
> > workload is run, and the raw profile data is collected from
> > /sys/kernel/debug/pgo/profraw.
> >
> > The raw profile data must be processed by clang's "llvm-profdata" tool
> > before it can be used during recompilation:
> >
> > $ cp /sys/kernel/debug/pgo/profraw vmlinux.profraw
> > $ llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw
> >
> > Multiple raw profiles may be merged during this step.
> >
> > The data can now be used by the compiler:
> >
> > $ make LLVM=1 KCFLAGS=-fprofile-use=vmlinux.profdata ...
> >
> > This initial submission is restricted to x86, as that's the platform we
> > know works. This restriction can be lifted once other platforms have
> > been verified to work with PGO.
> >
> > Note that this method of profiling the kernel is clang-native, unlike
> > the clang support in kernel/gcov.
> >
> > [1] https://clang.llvm.org/docs/UsersManual.html#profile-guided-optimization
> >
> > Signed-off-by: Sami Tolvanen <samitolvanen@xxxxxxxxxx>
> > Co-developed-by: Bill Wendling <morbo@xxxxxxxxxx>
> > Signed-off-by: Bill Wendling <morbo@xxxxxxxxxx>
> > ---
> > v2: - Added "__llvm_profile_instrument_memop" based on Nathan Chancellor's
> > testing.
> > - Corrected documentation, re PGO flags when using LTO, based on Fangrui
> > Song's comments.
> > v3: - Added change log section based on Sedat Dilek's comments.
> > v4: - Remove non-x86 Makfile changes and se "hweight64" instead of using our
> > own popcount implementation, based on Nick Desaulniers's comment.
> > v5: - Correct padding calculation, discovered by Nathan Chancellor.
> > ---
> > Documentation/dev-tools/index.rst | 1 +
> > Documentation/dev-tools/pgo.rst | 127 +++++++++
> > MAINTAINERS | 9 +
> > Makefile | 3 +
> > arch/Kconfig | 1 +
> > arch/x86/Kconfig | 1 +
> > arch/x86/boot/Makefile | 1 +
> > arch/x86/boot/compressed/Makefile | 1 +
> > arch/x86/crypto/Makefile | 2 +
> > arch/x86/entry/vdso/Makefile | 1 +
> > arch/x86/kernel/vmlinux.lds.S | 2 +
> > arch/x86/platform/efi/Makefile | 1 +
> > arch/x86/purgatory/Makefile | 1 +
> > arch/x86/realmode/rm/Makefile | 1 +
> > arch/x86/um/vdso/Makefile | 1 +
> > drivers/firmware/efi/libstub/Makefile | 1 +
> > include/asm-generic/vmlinux.lds.h | 44 +++
> > kernel/Makefile | 1 +
> > kernel/pgo/Kconfig | 35 +++
> > kernel/pgo/Makefile | 5 +
> > kernel/pgo/fs.c | 382 ++++++++++++++++++++++++++
> > kernel/pgo/instrument.c | 185 +++++++++++++
> > kernel/pgo/pgo.h | 206 ++++++++++++++
> > scripts/Makefile.lib | 10 +
> > 24 files changed, 1022 insertions(+)
> > create mode 100644 Documentation/dev-tools/pgo.rst
> > create mode 100644 kernel/pgo/Kconfig
> > create mode 100644 kernel/pgo/Makefile
> > create mode 100644 kernel/pgo/fs.c
> > create mode 100644 kernel/pgo/instrument.c
> > create mode 100644 kernel/pgo/pgo.h
> >
> > diff --git a/Documentation/dev-tools/index.rst b/Documentation/dev-tools/index.rst
> > index f7809c7b1ba9e..8d6418e858062 100644
> > --- a/Documentation/dev-tools/index.rst
> > +++ b/Documentation/dev-tools/index.rst
> > @@ -26,6 +26,7 @@ whole; patches welcome!
> > kgdb
> > kselftest
> > kunit/index
> > + pgo
> >
> >
> > .. only:: subproject and html
> > diff --git a/Documentation/dev-tools/pgo.rst b/Documentation/dev-tools/pgo.rst
> > new file mode 100644
> > index 0000000000000..b7f11d8405b73
> > --- /dev/null
> > +++ b/Documentation/dev-tools/pgo.rst
> > @@ -0,0 +1,127 @@
> > +.. SPDX-License-Identifier: GPL-2.0
> > +
> > +===============================
> > +Using PGO with the Linux kernel
> > +===============================
> > +
> > +Clang's profiling kernel support (PGO_) enables profiling of the Linux kernel
> > +when building with Clang. The profiling data is exported via the ``pgo``
> > +debugfs directory.
> > +
> > +.. _PGO: https://clang.llvm.org/docs/UsersManual.html#profile-guided-optimization
> > +
> > +
> > +Preparation
> > +===========
> > +
> > +Configure the kernel with:
> > +
> > +.. code-block:: make
> > +
> > + CONFIG_DEBUG_FS=y
> > + CONFIG_PGO_CLANG=y
> > +
> > +Note that kernels compiled with profiling flags will be significantly larger
> > +and run slower.
> > +
> > +Profiling data will only become accessible once debugfs has been mounted:
> > +
> > +.. code-block:: sh
> > +
> > + mount -t debugfs none /sys/kernel/debug
> > +
> > +
> > +Customization
> > +=============
> > +
> > +You can enable or disable profiling for individual file and directories by
> > +adding a line similar to the following to the respective kernel Makefile:
> > +
> > +- For a single file (e.g. main.o)
> > +
> > + .. code-block:: make
> > +
> > + PGO_PROFILE_main.o := y
> > +
> > +- For all files in one directory
> > +
> > + .. code-block:: make
> > +
> > + PGO_PROFILE := y
> > +
> > +To exclude files from being profiled use
> > +
> > + .. code-block:: make
> > +
> > + PGO_PROFILE_main.o := n
> > +
> > +and
> > +
> > + .. code-block:: make
> > +
> > + PGO_PROFILE := n
> > +
> > +Only files which are linked to the main kernel image or are compiled as kernel
> > +modules are supported by this mechanism.
> > +
> > +
> > +Files
> > +=====
> > +
> > +The PGO kernel support creates the following files in debugfs:
> > +
> > +``/sys/kernel/debug/pgo``
> > + Parent directory for all PGO-related files.
> > +
> > +``/sys/kernel/debug/pgo/reset``
> > + Global reset file: resets all coverage data to zero when written to.
> > +
> > +``/sys/kernel/debug/profraw``
> > + The raw PGO data that must be processed with ``llvm_profdata``.
> > +
> > +
> > +Workflow
> > +========
> > +
> > +The PGO kernel can be run on the host or test machines. The data though should
> > +be analyzed with Clang's tools from the same Clang version as the kernel was
> > +compiled. Clang's tolerant of version skew, but it's easier to use the same
> > +Clang version.
> > +
> > +The profiling data is useful for optimizing the kernel, analyzing coverage,
> > +etc. Clang offers tools to perform these tasks.
> > +
> > +Here is an example workflow for profiling an instrumented kernel with PGO and
> > +using the result to optimize the kernel:
> > +
> > +1) Install the kernel on the TEST machine.
> > +
> > +2) Reset the data counters right before running the load tests
> > +
> > + .. code-block:: sh
> > +
> > + $ echo 1 > /sys/kernel/debug/pgo/reset
> > +
> > +3) Run the load tests.
> > +
> > +4) Collect the raw profile data
> > +
> > + .. code-block:: sh
> > +
> > + $ cp -a /sys/kernel/debug/pgo/profraw /tmp/vmlinux.profraw
> > +
> > +5) (Optional) Download the raw profile data to the HOST machine.
> > +
> > +6) Process the raw profile data
> > +
> > + .. code-block:: sh
> > +
> > + $ llvm-profdata merge --output=vmlinux.profdata vmlinux.profraw
> > +
> > + Note that multiple raw profile data files can be merged during this step.
> > +
> > +7) Rebuild the kernel using the profile data (PGO disabled)
> > +
> > + .. code-block:: sh
> > +
> > + $ make LLVM=1 KCFLAGS=-fprofile-use=vmlinux.profdata ...
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index 79b400c97059f..cb1f1f2b2baf4 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -13948,6 +13948,15 @@ S: Maintained
> > F: include/linux/personality.h
> > F: include/uapi/linux/personality.h
> >
> > +PGO BASED KERNEL PROFILING
> > +M: Sami Tolvanen <samitolvanen@xxxxxxxxxx>
> > +M: Bill Wendling <wcw@xxxxxxxxxx>
> > +R: Nathan Chancellor <natechancellor@xxxxxxxxx>
> > +R: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> > +S: Supported
> > +F: Documentation/dev-tools/pgo.rst
> > +F: kernel/pgo
> > +
> > PHOENIX RC FLIGHT CONTROLLER ADAPTER
> > M: Marcus Folkesson <marcus.folkesson@xxxxxxxxx>
> > L: linux-input@xxxxxxxxxxxxxxx
> > diff --git a/Makefile b/Makefile
> > index 9e73f82e0d863..9128bfe1ccc97 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -659,6 +659,9 @@ endif # KBUILD_EXTMOD
> > # Defaults to vmlinux, but the arch makefile usually adds further targets
> > all: vmlinux
> >
> > +CFLAGS_PGO_CLANG := -fprofile-generate
> > +export CFLAGS_PGO_CLANG
> > +
> > CFLAGS_GCOV := -fprofile-arcs -ftest-coverage \
> > $(call cc-option,-fno-tree-loop-im) \
> > $(call cc-disable-warning,maybe-uninitialized,)
> > diff --git a/arch/Kconfig b/arch/Kconfig
> > index 24862d15f3a36..f39d3991f6bfe 100644
> > --- a/arch/Kconfig
> > +++ b/arch/Kconfig
> > @@ -1112,6 +1112,7 @@ config ARCH_SPLIT_ARG64
> > pairs of 32-bit arguments, select this option.
> >
> > source "kernel/gcov/Kconfig"
> > +source "kernel/pgo/Kconfig"
> >
> > source "scripts/gcc-plugins/Kconfig"
> >
> > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> > index 21f851179ff08..36305ea61dc09 100644
> > --- a/arch/x86/Kconfig
> > +++ b/arch/x86/Kconfig
> > @@ -96,6 +96,7 @@ config X86
> > select ARCH_SUPPORTS_DEBUG_PAGEALLOC
> > select ARCH_SUPPORTS_NUMA_BALANCING if X86_64
> > select ARCH_SUPPORTS_KMAP_LOCAL_FORCE_MAP if NR_CPUS <= 4096
> > + select ARCH_SUPPORTS_PGO_CLANG if X86_64
> > select ARCH_USE_BUILTIN_BSWAP
> > select ARCH_USE_QUEUED_RWLOCKS
> > select ARCH_USE_QUEUED_SPINLOCKS
> > diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile
> > index fe605205b4ce2..383853e32f673 100644
> > --- a/arch/x86/boot/Makefile
> > +++ b/arch/x86/boot/Makefile
> > @@ -71,6 +71,7 @@ KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__
> > KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=)
> > KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
> > GCOV_PROFILE := n
> > +PGO_PROFILE := n
> > UBSAN_SANITIZE := n
> >
> > $(obj)/bzImage: asflags-y := $(SVGA_MODE)
> > diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile
> > index e0bc3988c3faa..ed12ab65f6065 100644
> > --- a/arch/x86/boot/compressed/Makefile
> > +++ b/arch/x86/boot/compressed/Makefile
> > @@ -54,6 +54,7 @@ CFLAGS_sev-es.o += -I$(objtree)/arch/x86/lib/
> >
> > KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__
> > GCOV_PROFILE := n
> > +PGO_PROFILE := n
> > UBSAN_SANITIZE :=n
> >
> > KBUILD_LDFLAGS := -m elf_$(UTS_MACHINE)
> > diff --git a/arch/x86/crypto/Makefile b/arch/x86/crypto/Makefile
> > index a31de0c6ccde2..775fa0b368e98 100644
> > --- a/arch/x86/crypto/Makefile
> > +++ b/arch/x86/crypto/Makefile
> > @@ -4,6 +4,8 @@
> >
> > OBJECT_FILES_NON_STANDARD := y
> >
> > +PGO_PROFILE_curve25519-x86_64.o := n
> > +
>
> ^ Do you have more info about this?
>
This gave an error during compilation complaining about lacking
registers in some instances. This file is mostly inline asm or code
that doesn't super benefit from profiling, so I disabled it.
Note that the register issue happens only with PGO. Normal compilation is fine.
> > obj-$(CONFIG_CRYPTO_GLUE_HELPER_X86) += glue_helper.o
> >
> > obj-$(CONFIG_CRYPTO_TWOFISH_586) += twofish-i586.o
> > diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
> > index 02e3e42f380bd..26e2b3af0145c 100644
> > --- a/arch/x86/entry/vdso/Makefile
> > +++ b/arch/x86/entry/vdso/Makefile
> > @@ -179,6 +179,7 @@ quiet_cmd_vdso = VDSO $@
> > VDSO_LDFLAGS = -shared --hash-style=both --build-id=sha1 \
> > $(call ld-option, --eh-frame-hdr) -Bsymbolic
> > GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >
> > quiet_cmd_vdso_and_check = VDSO $@
> > cmd_vdso_and_check = $(cmd_vdso); $(cmd_vdso_check)
> > diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
> > index efd9e9ea17f25..f6cab2316c46a 100644
> > --- a/arch/x86/kernel/vmlinux.lds.S
> > +++ b/arch/x86/kernel/vmlinux.lds.S
> > @@ -184,6 +184,8 @@ SECTIONS
> >
> > BUG_TABLE
> >
> > + PGO_CLANG_DATA
> > +
> > ORC_UNWIND_TABLE
> >
> > . = ALIGN(PAGE_SIZE);
> > diff --git a/arch/x86/platform/efi/Makefile b/arch/x86/platform/efi/Makefile
> > index 84b09c230cbd5..5f22b31446ad4 100644
> > --- a/arch/x86/platform/efi/Makefile
> > +++ b/arch/x86/platform/efi/Makefile
> > @@ -2,6 +2,7 @@
> > OBJECT_FILES_NON_STANDARD_efi_thunk_$(BITS).o := y
> > KASAN_SANITIZE := n
> > GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >
> > obj-$(CONFIG_EFI) += quirks.o efi.o efi_$(BITS).o efi_stub_$(BITS).o
> > obj-$(CONFIG_EFI_MIXED) += efi_thunk_$(BITS).o
> > diff --git a/arch/x86/purgatory/Makefile b/arch/x86/purgatory/Makefile
> > index 95ea17a9d20cb..36f20e99da0bc 100644
> > --- a/arch/x86/purgatory/Makefile
> > +++ b/arch/x86/purgatory/Makefile
> > @@ -23,6 +23,7 @@ targets += purgatory.ro purgatory.chk
> >
> > # Sanitizer, etc. runtimes are unavailable and cannot be linked here.
> > GCOV_PROFILE := n
> > +PGO_PROFILE := n
> > KASAN_SANITIZE := n
> > UBSAN_SANITIZE := n
> > KCSAN_SANITIZE := n
> > diff --git a/arch/x86/realmode/rm/Makefile b/arch/x86/realmode/rm/Makefile
> > index 83f1b6a56449f..21797192f958f 100644
> > --- a/arch/x86/realmode/rm/Makefile
> > +++ b/arch/x86/realmode/rm/Makefile
> > @@ -76,4 +76,5 @@ KBUILD_CFLAGS := $(REALMODE_CFLAGS) -D_SETUP -D_WAKEUP \
> > KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__
> > KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
> > GCOV_PROFILE := n
> > +PGO_PROFILE := n
> > UBSAN_SANITIZE := n
> > diff --git a/arch/x86/um/vdso/Makefile b/arch/x86/um/vdso/Makefile
> > index 5943387e3f357..54f5768f58530 100644
> > --- a/arch/x86/um/vdso/Makefile
> > +++ b/arch/x86/um/vdso/Makefile
> > @@ -64,6 +64,7 @@ quiet_cmd_vdso = VDSO $@
> >
> > VDSO_LDFLAGS = -fPIC -shared -Wl,--hash-style=sysv
> > GCOV_PROFILE := n
> > +PGO_PROFILE := n
> >
> > #
> > # Install the unstripped copy of vdso*.so listed in $(vdso-install-y).
> > diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile
> > index 8a94388e38b33..2d81623b33f29 100644
> > --- a/drivers/firmware/efi/libstub/Makefile
> > +++ b/drivers/firmware/efi/libstub/Makefile
> > @@ -40,6 +40,7 @@ KBUILD_CFLAGS := $(cflags-y) -Os -DDISABLE_BRANCH_PROFILING \
> > KBUILD_CFLAGS := $(filter-out $(CC_FLAGS_SCS), $(KBUILD_CFLAGS))
> >
> > GCOV_PROFILE := n
> > +PGO_PROFILE := n
> > # Sanitizer runtimes are unavailable and cannot be linked here.
> > KASAN_SANITIZE := n
> > KCSAN_SANITIZE := n
> > diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> > index b2b3d81b1535a..3a591bb18c5fb 100644
> > --- a/include/asm-generic/vmlinux.lds.h
> > +++ b/include/asm-generic/vmlinux.lds.h
> > @@ -316,6 +316,49 @@
> > #define THERMAL_TABLE(name)
> > #endif
> >
> > +#ifdef CONFIG_PGO_CLANG
> > +#define PGO_CLANG_DATA \
> > + __llvm_prf_data : AT(ADDR(__llvm_prf_data) - LOAD_OFFSET) { \
> > + . = ALIGN(8); \
> > + __llvm_prf_start = .; \
> > + __llvm_prf_data_start = .; \
> > + KEEP(*(__llvm_prf_data)) \
> > + . = ALIGN(8); \
> > + __llvm_prf_data_end = .; \
> > + } \
> > + __llvm_prf_cnts : AT(ADDR(__llvm_prf_cnts) - LOAD_OFFSET) { \
> > + . = ALIGN(8); \
> > + __llvm_prf_cnts_start = .; \
> > + KEEP(*(__llvm_prf_cnts)) \
> > + . = ALIGN(8); \
> > + __llvm_prf_cnts_end = .; \
> > + } \
> > + __llvm_prf_names : AT(ADDR(__llvm_prf_names) - LOAD_OFFSET) { \
> > + . = ALIGN(8); \
> > + __llvm_prf_names_start = .; \
> > + KEEP(*(__llvm_prf_names)) \
> > + . = ALIGN(8); \
> > + __llvm_prf_names_end = .; \
> > + . = ALIGN(8); \
> > + } \
> > + __llvm_prf_vals : AT(ADDR(__llvm_prf_vals) - LOAD_OFFSET) { \
> > + __llvm_prf_vals_start = .; \
> > + KEEP(*(__llvm_prf_vals)) \
> > + . = ALIGN(8); \
> > + __llvm_prf_vals_end = .; \
> > + . = ALIGN(8); \
> > + } \
> > + __llvm_prf_vnds : AT(ADDR(__llvm_prf_vnds) - LOAD_OFFSET) { \
> > + __llvm_prf_vnds_start = .; \
> > + KEEP(*(__llvm_prf_vnds)) \
> > + . = ALIGN(8); \
> > + __llvm_prf_vnds_end = .; \
> > + __llvm_prf_end = .; \
> > + }
> > +#else
> > +#define PGO_CLANG_DATA
> > +#endif
> > +
> > #define KERNEL_DTB() \
> > STRUCT_ALIGN(); \
> > __dtb_start = .; \
> > @@ -1125,6 +1168,7 @@
> > CONSTRUCTORS \
> > } \
> > BUG_TABLE \
> > + PGO_CLANG_DATA
>
> ^ since dropping other arch support from v4, could probably drop this,
> too. We should be covered by the modification to
> arch/x86/kernel/vmlinux.lds.S, right?
>
Possibly, but I'd like to keep it here anyway. It's the correct place
for this info, and will benefit us when we do enable other platforms.
> >
> > #define INIT_TEXT_SECTION(inittext_align) \
> > . = ALIGN(inittext_align); \
> > diff --git a/kernel/Makefile b/kernel/Makefile
> > index aa7368c7eabf3..0b34ca228ba46 100644
> > --- a/kernel/Makefile
> > +++ b/kernel/Makefile
> > @@ -111,6 +111,7 @@ obj-$(CONFIG_BPF) += bpf/
> > obj-$(CONFIG_KCSAN) += kcsan/
> > obj-$(CONFIG_SHADOW_CALL_STACK) += scs.o
> > obj-$(CONFIG_HAVE_STATIC_CALL_INLINE) += static_call.o
> > +obj-$(CONFIG_PGO_CLANG) += pgo/
> >
> > obj-$(CONFIG_PERF_EVENTS) += events/
> >
> > diff --git a/kernel/pgo/Kconfig b/kernel/pgo/Kconfig
> > new file mode 100644
> > index 0000000000000..76a640b6cf6ed
> > --- /dev/null
> > +++ b/kernel/pgo/Kconfig
> > @@ -0,0 +1,35 @@
> > +# SPDX-License-Identifier: GPL-2.0-only
> > +menu "Profile Guided Optimization (PGO) (EXPERIMENTAL)"
> > +
> > +config ARCH_SUPPORTS_PGO_CLANG
> > + bool
> > +
> > +config PGO_CLANG
> > + bool "Enable clang's PGO-based kernel profiling"
> > + depends on DEBUG_FS
> > + depends on ARCH_SUPPORTS_PGO_CLANG
> > + depends on CC_IS_CLANG && CLANG_VERSION >= 120000
> > + help
> > + This option enables clang's PGO (Profile Guided Optimization) based
> > + code profiling to better optimize the kernel.
> > +
> > + If unsure, say N.
> > +
> > + Run a representative workload for your application on a kernel
> > + compiled with this option and download the raw profile file from
> > + /sys/kernel/debug/pgo/profraw. This file needs to be processed with
> > + llvm-profdata. It may be merged with other collected raw profiles.
> > +
> > + Copy the resulting profile file into vmlinux.profdata, and enable
> > + KCFLAGS=-fprofile-use=vmlinux.profdata to produce an optimized
> > + kernel.
> > +
> > + Note that a kernel compiled with profiling flags will be
> > + significantly larger and run slower. Also be sure to exclude files
> > + from profiling which are not linked to the kernel image to prevent
> > + linker errors.
> > +
> > + Note that the debugfs filesystem has to be mounted to access
> > + profiling data.
> > +
> > +endmenu
> > diff --git a/kernel/pgo/Makefile b/kernel/pgo/Makefile
> > new file mode 100644
> > index 0000000000000..41e27cefd9a47
> > --- /dev/null
> > +++ b/kernel/pgo/Makefile
> > @@ -0,0 +1,5 @@
> > +# SPDX-License-Identifier: GPL-2.0
> > +GCOV_PROFILE := n
> > +PGO_PROFILE := n
> > +
> > +obj-y += fs.o instrument.o
> > diff --git a/kernel/pgo/fs.c b/kernel/pgo/fs.c
> > new file mode 100644
> > index 0000000000000..68b24672be10a
> > --- /dev/null
> > +++ b/kernel/pgo/fs.c
> > @@ -0,0 +1,382 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright (C) 2019 Google, Inc.
> > + *
> > + * Author:
> > + * Sami Tolvanen <samitolvanen@xxxxxxxxxx>
> > + *
> > + * This software is licensed under the terms of the GNU General Public
> > + * License version 2, as published by the Free Software Foundation, and
> > + * may be copied, distributed, and modified under those terms.
> > + *
> > + * This program is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> > + * GNU General Public License for more details.
> > + *
> > + */
> > +
> > +#define pr_fmt(fmt) "pgo: " fmt
> > +
> > +#include <linux/kernel.h>
> > +#include <linux/debugfs.h>
> > +#include <linux/fs.h>
> > +#include <linux/module.h>
> > +#include <linux/slab.h>
> > +#include <linux/vmalloc.h>
> > +#include "pgo.h"
> > +
> > +static struct dentry *directory;
> > +
> > +struct prf_private_data {
> > + void *buffer;
> > + unsigned long size;
> > +};
> > +
> > +/*
> > + * Raw profile data format:
> > + *
> > + * - llvm_prf_header
> > + * - __llvm_prf_data
> > + * - __llvm_prf_cnts
> > + * - __llvm_prf_names
> > + * - zero padding to 8 bytes
> > + * - for each llvm_prf_data in __llvm_prf_data:
> > + * - llvm_prf_value_data
> > + * - llvm_prf_value_record + site count array
> > + * - llvm_prf_value_node_data
> > + * ...
> > + * ...
> > + * ...
> > + */
> > +
> > +static void prf_fill_header(void **buffer)
> > +{
> > + struct llvm_prf_header *header = *(struct llvm_prf_header **)buffer;
> > +
> > + header->magic = LLVM_PRF_MAGIC;
> > + header->version = LLVM_PRF_VARIANT_MASK_IR | LLVM_PRF_VERSION;
> > + header->data_size = prf_data_count();
> > + header->padding_bytes_before_counters = 0;
> > + header->counters_size = prf_cnts_count();
> > + header->padding_bytes_after_counters = 0;
> > + header->names_size = prf_names_count();
> > + header->counters_delta = (u64)__llvm_prf_cnts_start;
> > + header->names_delta = (u64)__llvm_prf_names_start;
> > + header->value_kind_last = LLVM_PRF_IPVK_LAST;
> > +
> > + *buffer += sizeof(*header);
> > +}
> > +
> > +/*
> > + * Copy the source into the buffer, incrementing the pointer into buffer in the
> > + * process.
> > + */
> > +static void prf_copy_to_buffer(void **buffer, void *src, unsigned long size)
> > +{
> > + memcpy(*buffer, src, size);
> > + *buffer += size;
> > +}
> > +
> > +static u32 __prf_get_value_size(struct llvm_prf_data *p, u32 *value_kinds)
> > +{
> > + struct llvm_prf_value_node **nodes =
> > + (struct llvm_prf_value_node **)p->values;
> > + u32 kinds = 0;
> > + u32 size = 0;
> > + unsigned int kind;
> > + unsigned int n;
> > + unsigned int s = 0;
> > +
> > + for (kind = 0; kind < ARRAY_SIZE(p->num_value_sites); kind++) {
> > + unsigned int sites = p->num_value_sites[kind];
> > +
> > + if (!sites)
> > + continue;
> > +
> > + /* Record + site count array */
> > + size += prf_get_value_record_size(sites);
> > + kinds++;
> > +
> > + if (!nodes)
> > + continue;
> > +
> > + for (n = 0; n < sites; n++) {
> > + u32 count = 0;
> > + struct llvm_prf_value_node *site = nodes[s + n];
> > +
> > + while (site && ++count <= U8_MAX)
> > + site = site->next;
> > +
> > + size += count *
> > + sizeof(struct llvm_prf_value_node_data);
> > + }
> > +
> > + s += sites;
> > + }
> > +
> > + if (size)
> > + size += sizeof(struct llvm_prf_value_data);
> > +
> > + if (value_kinds)
> > + *value_kinds = kinds;
> > +
> > + return size;
> > +}
> > +
> > +static u32 prf_get_value_size(void)
> > +{
> > + u32 size = 0;
> > + struct llvm_prf_data *p;
> > +
> > + for (p = __llvm_prf_data_start; p < __llvm_prf_data_end; p++)
> > + size += __prf_get_value_size(p, NULL);
> > +
> > + return size;
> > +}
> > +
> > +/* Serialize the profiling's value. */
> > +static void prf_serialize_value(struct llvm_prf_data *p, void **buffer)
> > +{
> > + struct llvm_prf_value_data header;
> > + struct llvm_prf_value_node **nodes =
> > + (struct llvm_prf_value_node **)p->values;
> > + unsigned int kind;
> > + unsigned int n;
> > + unsigned int s = 0;
> > +
> > + header.total_size = __prf_get_value_size(p, &header.num_value_kinds);
> > +
> > + if (!header.num_value_kinds)
> > + /* Nothing to write. */
> > + return;
> > +
> > + prf_copy_to_buffer(buffer, &header, sizeof(header));
> > +
> > + for (kind = 0; kind < ARRAY_SIZE(p->num_value_sites); kind++) {
> > + struct llvm_prf_value_record *record;
> > + u8 *counts;
> > + unsigned int sites = p->num_value_sites[kind];
> > +
> > + if (!sites)
> > + continue;
> > +
> > + /* Profiling value record. */
> > + record = *(struct llvm_prf_value_record **)buffer;
> > + *buffer += prf_get_value_record_header_size();
> > +
> > + record->kind = kind;
> > + record->num_value_sites = sites;
> > +
> > + /* Site count array. */
> > + counts = *(u8 **)buffer;
> > + *buffer += prf_get_value_record_site_count_size(sites);
> > +
> > + /*
> > + * If we don't have nodes, we can skip updating the site count
> > + * array, because the buffer is zero filled.
> > + */
> > + if (!nodes)
> > + continue;
> > +
> > + for (n = 0; n < sites; n++) {
> > + u32 count = 0;
> > + struct llvm_prf_value_node *site = nodes[s + n];
> > +
> > + while (site && ++count <= U8_MAX) {
> > + prf_copy_to_buffer(buffer, site,
> > + sizeof(struct llvm_prf_value_node_data));
> > + site = site->next;
> > + }
> > +
> > + counts[n] = (u8)count;
> > + }
> > +
> > + s += sites;
> > + }
> > +}
> > +
> > +static void prf_serialize_values(void **buffer)
> > +{
> > + struct llvm_prf_data *p;
> > +
> > + for (p = __llvm_prf_data_start; p < __llvm_prf_data_end; p++)
> > + prf_serialize_value(p, buffer);
> > +}
> > +
> > +static inline unsigned long prf_get_padding(unsigned long size)
> > +{
> > + return 7 & (8 - size % 8);
> > +}
>
> This is ugly but it looks like this corresponds with
> __llvm_profile_get_num_padding_bytes() in
> llvm-project/compiler-rt/lib/profile/InstrProfiling.c? If there are
> platforms where `sizeof(unsigned long) != 8` and are supported by the
> kernel, it might be nicer to spell out `sizeof(unsigned long)` rather
> than hardcode 8. Should we also use u64 for the parameter and u8 for
> the return type?
>
It's probably best to use what llvm uses in that function
(sizeof(uint64_t)). I can replace it.
> > +
> > +static unsigned long prf_buffer_size(void)
> > +{
> > + return sizeof(struct llvm_prf_header) +
> > + prf_data_size() +
> > + prf_cnts_size() +
> > + prf_names_size() +
> > + prf_get_padding(prf_names_size()) +
> > + prf_get_value_size();
> > +}
> > +
> > +/* Serialize the profiling data into a format LLVM's tools can understand. */
> > +static int prf_serialize(struct prf_private_data *p)
> > +{
> > + int err = 0;
> > + void *buffer;
> > +
> > + p->size = prf_buffer_size();
> > + p->buffer = vzalloc(p->size);
> > +
> > + if (!p->buffer) {
> > + err = -ENOMEM;
> > + goto out;
> > + }
> > +
> > + buffer = p->buffer;
> > +
> > + prf_fill_header(&buffer);
> > + prf_copy_to_buffer(&buffer, __llvm_prf_data_start, prf_data_size());
> > + prf_copy_to_buffer(&buffer, __llvm_prf_cnts_start, prf_cnts_size());
> > + prf_copy_to_buffer(&buffer, __llvm_prf_names_start, prf_names_size());
> > + buffer += prf_get_padding(prf_names_size());
> > +
> > + prf_serialize_values(&buffer);
> > +
> > +out:
> > + return err;
> > +}
> > +
> > +/* open() implementation for PGO. Creates a copy of the profiling data set. */
> > +static int prf_open(struct inode *inode, struct file *file)
> > +{
> > + struct prf_private_data *data;
> > + unsigned long flags;
> > + int err;
> > +
> > + data = kzalloc(sizeof(*data), GFP_KERNEL);
> > + if (!data) {
> > + err = -ENOMEM;
> > + goto out;
> > + }
> > +
> > + flags = prf_lock();
> > +
> > + err = prf_serialize(data);
> > + if (err) {
> > + kfree(data);
> > + goto out_unlock;
> > + }
> > +
> > + file->private_data = data;
> > +
> > +out_unlock:
> > + prf_unlock(flags);
>
> This is an improvement over earlier editions, but kfree() is still
> within the critical section. I wonder if it can be moved out? If not,
> why, precisely? Otherwise are we sure we have the concurrency correct?
> Might be worth pursuing in a follow up patch once the core has landed.
>
The kfree() isn't on the critical path, but done only when an error
occurs. I could add an "unlikely()" in the if-conditional hoping that
it's moved out-of-line, but the code it would be skipping would be a
couple of asm instructions. While I appreciate that performance in the
kernel is super important, we've already warned that performance with
an instrumented kernel won't be as good. :-)
> Also, it looks like the comment above the definition of pgo_lock and
> allocate_node() seem to indicate the same lock is used for
> serialization. I'm curious to know more about why we can't access
> current_node and serialize at the same time? At the least, it seems
> that `prf_serialize` should have a similar comment to `allocate_node`
> regarding the caller being expected to hold the `pgo_lock` via a call
> to `prf_lock()`, yeah?
>
> I can't help but look at the two call sites of prf_lock() and be
> suspicious that pgo_lock is technically guarding access to more
> variables than described in the comment. It would be good to explain
> exactly what is going on should we need to revisit the concurrency
> here in the future (and lower the bus factor).
>
I'll update the comments.
> > +out:
> > + return err;
> > +}
> > +
> > +/* read() implementation for PGO. */
> > +static ssize_t prf_read(struct file *file, char __user *buf, size_t count,
> > + loff_t *ppos)
> > +{
> > + struct prf_private_data *data = file->private_data;
> > +
> > + BUG_ON(!data);
> > +
> > + return simple_read_from_buffer(buf, count, ppos, data->buffer,
> > + data->size);
> > +}
> > +
> > +/* release() implementation for PGO. Release resources allocated by open(). */
> > +static int prf_release(struct inode *inode, struct file *file)
> > +{
> > + struct prf_private_data *data = file->private_data;
> > +
> > + if (data) {
> > + vfree(data->buffer);
> > + kfree(data);
> > + }
> > +
> > + return 0;
> > +}
> > +
> > +static const struct file_operations prf_fops = {
> > + .owner = THIS_MODULE,
> > + .open = prf_open,
> > + .read = prf_read,
> > + .llseek = default_llseek,
> > + .release = prf_release
> > +};
> > +
> > +/* write() implementation for resetting PGO's profile data. */
> > +static ssize_t reset_write(struct file *file, const char __user *addr,
> > + size_t len, loff_t *pos)
> > +{
> > + struct llvm_prf_data *data;
> > +
> > + memset(__llvm_prf_cnts_start, 0, prf_cnts_size());
> > +
> > + for (data = __llvm_prf_data_start; data < __llvm_prf_data_end; ++data) {
>
> ^ this patch mixes pre-increment and post-increment in loops. The
> kernel coding style docs (Documentation/process/coding-style.rst)
> don't make a call on this, but it might be nice to be internally
> consistent throughout the patch. I assume that's from having mixed
> authors. Not a huge issue, but I'm pedantic.
>
Okay.
> > + struct llvm_prf_value_node **vnodes;
> > + u64 current_vsite_count;
> > + u32 i;
> > +
> > + if (!data->values)
> > + continue;
> > +
> > + current_vsite_count = 0;
> > + vnodes = (struct llvm_prf_value_node **)data->values;
> > +
> > + for (i = LLVM_PRF_IPVK_FIRST; i <= LLVM_PRF_IPVK_LAST; ++i)
> > + current_vsite_count += data->num_value_sites[i];
> > +
> > + for (i = 0; i < current_vsite_count; ++i) {
> > + struct llvm_prf_value_node *current_vnode = vnodes[i];
> > +
> > + while (current_vnode) {
> > + current_vnode->count = 0;
> > + current_vnode = current_vnode->next;
> > + }
> > + }
> > + }
> > +
> > + return len;
> > +}
> > +
> > +static const struct file_operations prf_reset_fops = {
> > + .owner = THIS_MODULE,
> > + .write = reset_write,
> > + .llseek = noop_llseek,
> > +};
> > +
> > +/* Create debugfs entries. */
> > +static int __init pgo_init(void)
> > +{
> > + directory = debugfs_create_dir("pgo", NULL);
> > + if (!directory)
> > + goto err_remove;
> > +
> > + if (!debugfs_create_file("profraw", 0600, directory, NULL,
> > + &prf_fops))
> > + goto err_remove;
> > +
> > + if (!debugfs_create_file("reset", 0200, directory, NULL,
> > + &prf_reset_fops))
> > + goto err_remove;
> > +
> > + return 0;
> > +
> > +err_remove:
> > + pr_err("initialization failed\n");
> > + return -EIO;
> > +}
> > +
> > +/* Remove debugfs entries. */
> > +static void __exit pgo_exit(void)
> > +{
> > + debugfs_remove_recursive(directory);
> > +}
> > +
> > +module_init(pgo_init);
> > +module_exit(pgo_exit);
> > diff --git a/kernel/pgo/instrument.c b/kernel/pgo/instrument.c
> > new file mode 100644
> > index 0000000000000..6084ff0652e85
> > --- /dev/null
> > +++ b/kernel/pgo/instrument.c
> > @@ -0,0 +1,185 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright (C) 2019 Google, Inc.
> > + *
> > + * Author:
> > + * Sami Tolvanen <samitolvanen@xxxxxxxxxx>
> > + *
> > + * This software is licensed under the terms of the GNU General Public
> > + * License version 2, as published by the Free Software Foundation, and
> > + * may be copied, distributed, and modified under those terms.
> > + *
> > + * This program is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> > + * GNU General Public License for more details.
> > + *
> > + */
> > +
> > +#define pr_fmt(fmt) "pgo: " fmt
> > +
> > +#include <linux/bitops.h>
> > +#include <linux/kernel.h>
> > +#include <linux/export.h>
> > +#include <linux/spinlock.h>
> > +#include <linux/types.h>
> > +#include "pgo.h"
> > +
> > +/* Lock guarding value node access and serialization. */
> > +static DEFINE_SPINLOCK(pgo_lock);
> > +static int current_node;
> > +
> > +unsigned long prf_lock(void)
> > +{
> > + unsigned long flags;
> > +
> > + spin_lock_irqsave(&pgo_lock, flags);
> > +
> > + return flags;
> > +}
> > +
> > +void prf_unlock(unsigned long flags)
> > +{
> > + spin_unlock_irqrestore(&pgo_lock, flags);
> > +}
> > +
> > +/*
> > + * Return a newly allocated profiling value node which contains the tracked
> > + * value by the value profiler.
> > + * Note: caller *must* hold pgo_lock.
> > + */
> > +static struct llvm_prf_value_node *allocate_node(struct llvm_prf_data *p,
> > + u32 index, u64 value)
> > +{
> > + if (&__llvm_prf_vnds_start[current_node + 1] >= __llvm_prf_vnds_end)
> > + return NULL; /* Out of nodes */
> > +
> > + current_node++;
> > +
> > + /* Make sure the node is entirely within the section */
> > + if (&__llvm_prf_vnds_start[current_node] >= __llvm_prf_vnds_end ||
> > + &__llvm_prf_vnds_start[current_node + 1] > __llvm_prf_vnds_end)
> > + return NULL;
> > +
> > + return &__llvm_prf_vnds_start[current_node];
> > +}
> > +
> > +/*
> > + * Counts the number of times a target value is seen.
> > + *
> > + * Records the target value for the CounterIndex if not seen before. Otherwise,
> > + * increments the counter associated w/ the target value.
> > + */
> > +void __llvm_profile_instrument_target(u64 target_value, void *data, u32 index);
> > +void __llvm_profile_instrument_target(u64 target_value, void *data, u32 index)
> > +{
> > + struct llvm_prf_data *p = (struct llvm_prf_data *)data;
> > + struct llvm_prf_value_node **counters;
> > + struct llvm_prf_value_node *curr;
> > + struct llvm_prf_value_node *min = NULL;
> > + struct llvm_prf_value_node *prev = NULL;
> > + u64 min_count = U64_MAX;
> > + u8 values = 0;
> > + unsigned long flags;
> > +
> > + if (!p || !p->values)
> > + return;
> > +
> > + counters = (struct llvm_prf_value_node **)p->values;
> > + curr = counters[index];
> > +
> > + while (curr) {
> > + if (target_value == curr->value) {
> > + curr->count++;
> > + return;
> > + }
> > +
> > + if (curr->count < min_count) {
> > + min_count = curr->count;
> > + min = curr;
> > + }
> > +
> > + prev = curr;
> > + curr = curr->next;
> > + values++;
> > + }
> > +
> > + if (values >= LLVM_PRF_MAX_NUM_VALS_PER_SITE) {
> > + if (!min->count || !(--min->count)) {
> > + curr = min;
> > + curr->value = target_value;
> > + curr->count++;
> > + }
> > + return;
> > + }
> > +
> > + /* Lock when updating the value node structure. */
> > + flags = prf_lock();
> > +
> > + curr = allocate_node(p, index, target_value);
> > + if (!curr)
> > + goto out;
> > +
> > + curr->value = target_value;
> > + curr->count++;
> > +
> > + if (!counters[index])
> > + counters[index] = curr;
> > + else if (prev && !prev->next)
> > + prev->next = curr;
> > +
> > +out:
> > + prf_unlock(flags);
> > +}
> > +EXPORT_SYMBOL(__llvm_profile_instrument_target);
> > +
> > +/* Counts the number of times a range of targets values are seen. */
> > +void __llvm_profile_instrument_range(u64 target_value, void *data,
> > + u32 index, s64 precise_start,
> > + s64 precise_last, s64 large_value);
> > +void __llvm_profile_instrument_range(u64 target_value, void *data,
> > + u32 index, s64 precise_start,
> > + s64 precise_last, s64 large_value)
> > +{
> > + if (large_value != S64_MIN && (s64)target_value >= large_value)
> > + target_value = large_value;
> > + else if ((s64)target_value < precise_start ||
> > + (s64)target_value > precise_last)
> > + target_value = precise_last + 1;
> > +
> > + __llvm_profile_instrument_target(target_value, data, index);
> > +}
> > +EXPORT_SYMBOL(__llvm_profile_instrument_range);
> > +
> > +static u64 inst_prof_get_range_rep_value(u64 value)
> > +{
> > + if (value <= 8)
> > + /* The first ranges are individually tracked, us it as is. */
>
> ^ typo, "use"
>
> > + return value;
> > + else if (value >= 513)
> > + /* The last range is mapped to its lowest value. */
> > + return 513;
> > + else if (hweight64(value) == 1)
> > + /* If it's a power of two, use it as is. */
> > + return value;
> > +
> > + /* Otherwise, take to the previous power of two + 1. */
> > + return (1 << (64 - __builtin_clzll(value) - 1)) + 1;
> > +}
> > +
> > +/*
> > + * The target values are partitioned into multiple ranges. The range spec is
> > + * defined in compiler-rt/include/profile/InstrProfData.inc.
> > + */
> > +void __llvm_profile_instrument_memop(u64 target_value, void *data,
> > + u32 counter_index);
> > +void __llvm_profile_instrument_memop(u64 target_value, void *data,
> > + u32 counter_index)
> > +{
> > + u64 rep_value;
> > +
> > + /* Map the target value to the representative value of its range. */
> > + rep_value = inst_prof_get_range_rep_value(target_value);
> > + __llvm_profile_instrument_target(rep_value, data, counter_index);
> > +}
> > +EXPORT_SYMBOL(__llvm_profile_instrument_memop);
> > diff --git a/kernel/pgo/pgo.h b/kernel/pgo/pgo.h
> > new file mode 100644
> > index 0000000000000..df0aa278f28bd
> > --- /dev/null
> > +++ b/kernel/pgo/pgo.h
> > @@ -0,0 +1,206 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * Copyright (C) 2019 Google, Inc.
> > + *
> > + * Author:
> > + * Sami Tolvanen <samitolvanen@xxxxxxxxxx>
> > + *
> > + * This software is licensed under the terms of the GNU General Public
> > + * License version 2, as published by the Free Software Foundation, and
> > + * may be copied, distributed, and modified under those terms.
> > + *
> > + * This program is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> > + * GNU General Public License for more details.
> > + *
> > + */
> > +
> > +#ifndef _PGO_H
> > +#define _PGO_H
> > +
> > +/*
> > + * Note: These internal LLVM definitions must match the compiler version.
> > + * See llvm/include/llvm/ProfileData/InstrProfData.inc in LLVM's source code.
> > + */
> > +
> > +#ifdef CONFIG_64BIT
> > + #define LLVM_PRF_MAGIC \
> > + ((u64)255 << 56 | \
> > + (u64)'l' << 48 | \
> > + (u64)'p' << 40 | \
> > + (u64)'r' << 32 | \
> > + (u64)'o' << 24 | \
> > + (u64)'f' << 16 | \
> > + (u64)'r' << 8 | \
> > + (u64)129)
> > +#else
> > + #define LLVM_PRF_MAGIC \
> > + ((u64)255 << 56 | \
> > + (u64)'l' << 48 | \
> > + (u64)'p' << 40 | \
> > + (u64)'r' << 32 | \
> > + (u64)'o' << 24 | \
> > + (u64)'f' << 16 | \
> > + (u64)'R' << 8 | \
> > + (u64)129)
> > +#endif
> > +
> > +#define LLVM_PRF_VERSION 5
> > +#define LLVM_PRF_DATA_ALIGN 8
> > +#define LLVM_PRF_IPVK_FIRST 0
> > +#define LLVM_PRF_IPVK_LAST 1
> > +#define LLVM_PRF_MAX_NUM_VALS_PER_SITE 16
>
> llvm/include/llvm/ProfileData/InstrProfData.inc defines
> INSTR_PROF_MAX_NUM_VAL_PER_SITE as 255; does that need to match?
>
Sure. I also updated the names to better match LLVM's names.
> > +
> > +#define LLVM_PRF_VARIANT_MASK_IR (0x1ull << 56)
> > +#define LLVM_PRF_VARIANT_MASK_CSIR (0x1ull << 57)
> > +
> > +/**
> > + * struct llvm_prf_header - represents the raw profile header data structure.
> > + * @magic: the magic token for the file format.
> > + * @version: the version of the file format.
> > + * @data_size: the number of entries in the profile data section.
> > + * @padding_bytes_before_counters: the number of padding bytes before the
> > + * counters.
> > + * @counters_size: the size in bytes of the LLVM profile section containing the
> > + * counters.
> > + * @padding_bytes_after_counters: the number of padding bytes after the
> > + * counters.
> > + * @names_size: the size in bytes of the LLVM profile section containing the
> > + * counters' names.
> > + * @counters_delta: the beginning of the LLMV profile counters section.
> > + * @names_delta: the beginning of the LLMV profile names section.
> > + * @value_kind_last: the last profile value kind.
> > + */
> > +struct llvm_prf_header {
> > + u64 magic;
> > + u64 version;
> > + u64 data_size;
> > + u64 padding_bytes_before_counters;
> > + u64 counters_size;
> > + u64 padding_bytes_after_counters;
> > + u64 names_size;
> > + u64 counters_delta;
> > + u64 names_delta;
> > + u64 value_kind_last;
> > +};
> > +
> > +/**
> > + * struct llvm_prf_data - represents the per-function control structure.
> > + * @name_ref: the reference to the function's name.
> > + * @func_hash: the hash value of the function.
> > + * @counter_ptr: a pointer to the profile counter.
> > + * @function_ptr: a pointer to the function.
> > + * @values: the profiling values associated with this function.
> > + * @num_counters: the number of counters in the function.
> > + * @num_value_sites: the number of value profile sites.
> > + */
> > +struct llvm_prf_data {
> > + const u64 name_ref;
> > + const u64 func_hash;
> > + const void *counter_ptr;
> > + const void *function_ptr;
> > + void *values;
> > + const u32 num_counters;
> > + const u16 num_value_sites[LLVM_PRF_IPVK_LAST + 1];
> > +} __aligned(LLVM_PRF_DATA_ALIGN);
> > +
> > +/**
> > + * structure llvm_prf_value_node_data - represents the data part of the struct
> > + * llvm_prf_value_node data structure.
> > + * @value: the value counters.
> > + * @count: the counters' count.
> > + */
> > +struct llvm_prf_value_node_data {
> > + u64 value;
> > + u64 count;
> > +};
> > +
> > +/**
> > + * struct llvm_prf_value_node - represents an internal data structure used by
> > + * the value profiler.
> > + * @value: the value counters.
> > + * @count: the counters' count.
> > + * @next: the next value node.
> > + */
> > +struct llvm_prf_value_node {
> > + u64 value;
> > + u64 count;
> > + struct llvm_prf_value_node *next;
> > +};
> > +
> > +/**
> > + * struct llvm_prf_value_data - represents the value profiling data in indexed
> > + * format.
> > + * @total_size: the total size in bytes including this field.
> > + * @num_value_kinds: the number of value profile kinds that has value profile
> > + * data.
> > + */
> > +struct llvm_prf_value_data {
> > + u32 total_size;
> > + u32 num_value_kinds;
> > +};
> > +
> > +/**
> > + * struct llvm_prf_value_record - represents the on-disk layout of the value
> > + * profile data of a particular kind for one function.
> > + * @kind: the kind of the value profile record.
> > + * @num_value_sites: the number of value profile sites.
> > + * @site_count_array: the first element of the array that stores the number
> > + * of profiled values for each value site.
> > + */
> > +struct llvm_prf_value_record {
> > + u32 kind;
> > + u32 num_value_sites;
> > + u8 site_count_array[];
> > +};
> > +
> > +#define prf_get_value_record_header_size() \
> > + offsetof(struct llvm_prf_value_record, site_count_array)
> > +#define prf_get_value_record_site_count_size(sites) \
> > + roundup((sites), 8)
> > +#define prf_get_value_record_size(sites) \
> > + (prf_get_value_record_header_size() + \
> > + prf_get_value_record_site_count_size((sites)))
> > +
> > +/* Data sections */
> > +extern struct llvm_prf_data __llvm_prf_data_start[];
> > +extern struct llvm_prf_data __llvm_prf_data_end[];
> > +
> > +extern u64 __llvm_prf_cnts_start[];
> > +extern u64 __llvm_prf_cnts_end[];
> > +
> > +extern char __llvm_prf_names_start[];
> > +extern char __llvm_prf_names_end[];
> > +
> > +extern struct llvm_prf_value_node __llvm_prf_vnds_start[];
> > +extern struct llvm_prf_value_node __llvm_prf_vnds_end[];
> > +
> > +/* Locking for vnodes */
> > +extern unsigned long prf_lock(void);
> > +extern void prf_unlock(unsigned long flags);
> > +
> > +#define __DEFINE_PRF_SIZE(s) \
> > + static inline unsigned long prf_ ## s ## _size(void) \
> > + { \
> > + unsigned long start = \
> > + (unsigned long)__llvm_prf_ ## s ## _start; \
> > + unsigned long end = \
> > + (unsigned long)__llvm_prf_ ## s ## _end; \
> > + return roundup(end - start, \
> > + sizeof(__llvm_prf_ ## s ## _start[0])); \
> > + } \
> > + static inline unsigned long prf_ ## s ## _count(void) \
> > + { \
> > + return prf_ ## s ## _size() / \
> > + sizeof(__llvm_prf_ ## s ## _start[0]); \
> > + }
> > +
> > +__DEFINE_PRF_SIZE(data);
> > +__DEFINE_PRF_SIZE(cnts);
> > +__DEFINE_PRF_SIZE(names);
> > +__DEFINE_PRF_SIZE(vnds);
> > +
> > +#undef __DEFINE_PRF_SIZE
> > +
> > +#endif /* _PGO_H */
> > diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> > index 213677a5ed33e..9b218afb5cb87 100644
> > --- a/scripts/Makefile.lib
> > +++ b/scripts/Makefile.lib
> > @@ -143,6 +143,16 @@ _c_flags += $(if $(patsubst n%,, \
> > $(CFLAGS_GCOV))
> > endif
> >
> > +#
> > +# Enable clang's PGO profiling flags for a file or directory depending on
> > +# variables PGO_PROFILE_obj.o and PGO_PROFILE.
> > +#
> > +ifeq ($(CONFIG_PGO_CLANG),y)
> > +_c_flags += $(if $(patsubst n%,, \
> > + $(PGO_PROFILE_$(basetarget).o)$(PGO_PROFILE)y), \
> > + $(CFLAGS_PGO_CLANG))
> > +endif
> > +
> > #
> > # Enable address sanitizer flags for kernel except some files or directories
> > # we don't want to check (depends on variables KASAN_SANITIZE_obj.o, KASAN_SANITIZE)
> > --
> > 2.30.0.284.gd98b1dd5eaa7-goog
> >
Sending patch v6. PTAL.
-bw