On Wed, Apr 07, 2021 at 02:17:04PM -0700, 'Bill Wendling' via Clang Built Linux 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> > Tested-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > Reviewed-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > Reviewed-by: Fangrui Song <maskray@xxxxxxxxxx> Thanks for sending this again! I'm looking forward to using it. Masahiro and Andrew, unless one of you would prefer to take this in your tree, I figure I can snag it to send to Linus. Anyone else have feedback? Thanks! -Kees -- Kees Cook
