Messages in this thread | | | From | Marco Elver <> | Date | Wed, 27 May 2020 21:14:54 +0200 | Subject | Re: [PATCH -tip] compiler_types.h: Optimize __unqual_scalar_typeof compilation time |
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On Wed, 27 May 2020 at 21:11, Sedat Dilek <sedat.dilek@gmail.com> wrote: > > On Wed, May 27, 2020 at 3:57 PM Marco Elver <elver@google.com> wrote: > > > > On Wed, 27 May 2020 at 15:37, Sedat Dilek <sedat.dilek@gmail.com> wrote: > > > > > > On Wed, May 27, 2020 at 3:30 PM Marco Elver <elver@google.com> wrote: > > > > > > > > On Wed, 27 May 2020 at 15:11, Sedat Dilek <sedat.dilek@gmail.com> wrote: > > > > > > > > > > On Wed, May 27, 2020 at 2:50 PM Arnd Bergmann <arnd@arndb.de> wrote: > > > > > > > > > > > > On Wed, May 27, 2020 at 2:35 PM Sedat Dilek <sedat.dilek@gmail.com> wrote: > > > > > > > On Wed, May 27, 2020 at 2:31 PM Arnd Bergmann <arnd@arndb.de> wrote: > > > > > > > > On Wed, May 27, 2020 at 1:36 PM Sedat Dilek <sedat.dilek@gmail.com> wrote: > > > > > > > > > On Wed, May 27, 2020 at 1:27 PM Arnd Bergmann <arnd@arndb.de> wrote: > > > > > > > > > > On Wed, May 27, 2020 at 12:33 PM Marco Elver <elver@google.com> wrote: > > > > > > > > > > > > > > > > > > > > This gives us back 80% of the performance drop on clang, and 50% > > > > > > > > > > of the drop I saw with gcc, compared to current mainline. > > > > > > > > > > > > > > > > > > > > Tested-by: Arnd Bergmann <arnd@arndb.de> > > > > > > > > > > > > > > > > > > > > > > > > > > > > Hi Arnd, > > > > > > > > > > > > > > > > > > with "mainline" you mean Linux-next aka Linux v5.8 - not v5.7? > > > > > > > > > > > > > > > > I meant v5.7. > > > > > > > > > > > > > > > > > I have not seen __unqual_scalar_typeof(x) in compiler_types.h in Linux v5.7. > > > > > > > > > > > > > > > > > > Is there a speedup benefit also for Linux v5.7? > > > > > > > > > Which patches do I need? > > > > > > > > > > > > > > > > v5.7-rc is the baseline and is the fastest I currently see. On certain files, > > > > > > > > I saw an intermittent 10x slowdown that was already fixed earlier, now > > > > > > > > linux-next > > > > > > > > is more like 2x slowdown for me and 1.2x with this patch on top, so we're > > > > > > > > almost back to the speed of linux-5.7. > > > > > > > > > > > > > > > > > > > > > > Which clang version did you use - and have you set KCSAN kconfigs - > > > > > > > AFAICS this needs clang-11? > > > > > > > > > > > > I'm currently using clang-11, but I see the same problem with older > > > > > > versions, and both with and without KCSAN enabled. I think the issue > > > > > > is mostly the deep nesting of macros that leads to code bloat. > > > > > > > > > > > > > > > > Thanks. > > > > > > > > > > With clang-10: > > > > > > > > > > $ scripts/diffconfig /boot/config-5.7.0-rc7-2-amd64-clang .config > > > > > BUILD_SALT "5.7.0-rc7-2-amd64-clang" -> "5.7.0-rc7-3-amd64-clang" > > > > > +HAVE_ARCH_KCSAN y > > > > > > > > Clang 10 doesn't support KCSAN (HAVE_KCSAN_COMPILER unset). > > > > > > > > > With clang-11: > > > > > > > > > > $ scripts/diffconfig /boot/config-5.7.0-rc7-2-amd64-clang .config > > > > > BUILD_SALT "5.7.0-rc7-2-amd64-clang" -> "5.7.0-rc7-3-amd64-clang" > > > > > CLANG_VERSION 100001 -> 110000 > > > > > +CC_HAS_ASM_INLINE y > > > > > +HAVE_ARCH_KCSAN y > > > > > +HAVE_KCSAN_COMPILER y > > > > > +KCSAN n > > > > > > > > > > Which KCSAN kconfigs did you enable? > > > > > > > > To clarify: as said in [1], KCSAN (or any other instrumentation) is no > > > > longer relevant to the issue here, and the compile-time regression is > > > > observable with most configs. The problem is due to pre-processing and > > > > parsing, which came about due to new READ_ONCE() and the > > > > __unqual_scalar_typeof() macro (which this patch optimizes). > > > > > > > > KCSAN and new ONCEs got tangled up because we first attempted to > > > > annotate {READ,WRITE}_ONCE() with data_race(), but that turned out to > > > > have all kinds of other issues (explanation in [2]). So we decided to > > > > drop all the KCSAN-specific bits from ONCE, and require KCSAN to be > > > > Clang 11. Those fixes were applied to the first version of new > > > > {READ,WRITE}_ONCE() in -tip, which actually restored the new ONCEs to > > > > the pre-KCSAN version (now that KCSAN can deal with them without > > > > annotations). > > > > > > > > Hope this makes more sense now. > > > > > > > > [1] https://lore.kernel.org/lkml/CANpmjNOUdr2UG3F45=JaDa0zLwJ5ukPc1MMKujQtmYSmQnjcXg@mail.gmail.com/ > > > > [2] https://lore.kernel.org/lkml/20200521142047.169334-1-elver@google.com/ > > > > > > > > > > Thanks, Marco. > > > > > > I pulled tip.git#locking/kcsan on top of Linux v5.7-rc7 and applied this patch. > > > Just wanted to try KCSAN for the first time and it will also be my > > > first building with clang-11. > > > That's why I asked. > > > > In general, CONFIG_KCSAN=y and the defaults for the other KCSAN > > options should be good. Depending on the size of your system, you > > could also tweak KCSAN runtime performance: > > https://lwn.net/Articles/816850/#Interacting%20with%20KCSAN%20at%20Runtime > > -- the defaults should be good for most systems though. > > Hope this helps. Any more questions, do let me know. > > > > Which "projects" and packages do I need? > > I have installed: > > # LC_ALL=C apt-get install llvm-11 clang-11 lld-11 > --no-install-recommends -t llvm-toolchain -y > > # dpkg -l | grep > 1:11~++20200527111130+65030821d4a-1~exp1~20200527091804.3261 | awk > '/^ii/ {print $1 " " $2 " " $3}' | column -t > ii clang-11 > 1:11~++20200527111130+65030821d4a-1~exp1~20200527091804.3261 > ii libclang-common-11-dev > 1:11~++20200527111130+65030821d4a-1~exp1~20200527091804.3261 > ii libclang-cpp11 > 1:11~++20200527111130+65030821d4a-1~exp1~20200527091804.3261 > ii libclang1-11 > 1:11~++20200527111130+65030821d4a-1~exp1~20200527091804.3261 > ii libllvm11:amd64 > 1:11~++20200527111130+65030821d4a-1~exp1~20200527091804.3261 > ii lld-11 > 1:11~++20200527111130+65030821d4a-1~exp1~20200527091804.3261 > ii llvm-11 > 1:11~++20200527111130+65030821d4a-1~exp1~20200527091804.3261 > ii llvm-11-runtime > 1:11~++20200527111130+65030821d4a-1~exp1~20200527091804.3261 > > Is that enough?
Just clang-11 (and its transitive dependencies) is enough. Unsure what your installed binary is, likely "clang-11", so if you can do "make CC=clang-11 defconfig" (and check for CONFIG_HAVE_KCSAN_COMPILER) you're good to go.
Thanks, -- Marco
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