On Fri, Jan 22, 2021 at 2:34 AM Nick Desaulniers <ndesaulniers@xxxxxxxxxx> wrote: > > On Wed, Jan 20, 2021 at 6:21 PM Sedat Dilek <sedat.dilek@xxxxxxxxx> wrote: > > > > Hi, > > > > When I looked through the code I wondered why we do not add a > > "CONFIG_PGO_CLANG_PROFDATA" which can be helpful when doing the PGO > > rebuild with a vmlinux.profdata. > > > > This introduces a "PGO_PROFDATA" to turn on/off to pass > > "-fprofile-use=vmlinux.profdata" (see CFLAGS_PGO_CLANG_PROFDATA in > > top-level Makefile). > > > > If we turn off via "PGO_PROFILE := n" in several Makefiles - we should > > do the same and add "PGO_PROFDATA := n" to the same Makefiles? > > > > Please see the attached diff. > > This is a good idea; something that I brought up in initial code > review (on github). Would it be ok with you to land the core first, > then follow up with this suggestion? > > Also, AutoFDO production builds are so incredibly similar to PGO > builds that I could see a possible path forward: > 1. land PGO upstream > 2. adds docs for AutoFDO > 3. consider a config for hardcoding the location of the profiling data > so that we don't need to specify it at the command line invocation of > make. > I made a v3 - with some small nits. The idea was to do the "PGO-rebuild" handling a bit easier. But as you say that can wait. Some personal notes: I will be very happy when people verify/confirm what's going on with PGO-rebuild + LLVM_IAS=1. As said GNU/AS and PGO-rebuild is fine. ( This seems to be independent of clang-12 or clang-11. ) ( This seems to be independent of DWARF v4 or v5 enabled. ) The benefit here I saw was a reduction in build-time of 00:30 seen from a total 04:30 when using a PGO-rebuilt Linux-kernel. Approx. 10%? This is not much compared to a ThinLTO + PGO optimized LLVM toolchain whcih saved here 40% of build-time. - Sedat -
