On Wed, May 27, 2020 at 9:15 PM Marco Elver wrote: > > On Wed, 27 May 2020 at 21:11, Sedat Dilek wrote: > > > > On Wed, May 27, 2020 at 3:57 PM Marco Elver wrote: > > > > > > On Wed, 27 May 2020 at 15:37, Sedat Dilek wrote: > > > > > > > > On Wed, May 27, 2020 at 3:30 PM Marco Elver wrote: > > > > > > > > > > On Wed, 27 May 2020 at 15:11, Sedat Dilek wrote: > > > > > > > > > > > > On Wed, May 27, 2020 at 2:50 PM Arnd Bergmann wrote: > > > > > > > > > > > > > > On Wed, May 27, 2020 at 2:35 PM Sedat Dilek wrote: > > > > > > > > On Wed, May 27, 2020 at 2:31 PM Arnd Bergmann wrote: > > > > > > > > > On Wed, May 27, 2020 at 1:36 PM Sedat Dilek wrote: > > > > > > > > > > On Wed, May 27, 2020 at 1:27 PM Arnd Bergmann wrote: > > > > > > > > > > > On Wed, May 27, 2020 at 12:33 PM Marco Elver 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 > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > 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. > I was able to build with clang-11 from apt.llvm.org. [ build-time ] Normally, it takes me approx. 05:00 to build with clang-10 (10.0.1-rc1) and Linux v5.7-rc7. This time start: 21:18 and stop: 03:45 means 06:27 - took 01:27 longer. Samsung Ultrabook 2nd generation aka Intel Sandybridge CPU with 'make -j3'. [ diffconfig ] 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 y +KCSAN_ASSUME_PLAIN_WRITES_ATOMIC y +KCSAN_DEBUG n +KCSAN_DELAY_RANDOMIZE y +KCSAN_EARLY_ENABLE y +KCSAN_IGNORE_ATOMICS n +KCSAN_INTERRUPT_WATCHER n +KCSAN_NUM_WATCHPOINTS 64 +KCSAN_REPORT_ONCE_IN_MS 3000 +KCSAN_REPORT_RACE_UNKNOWN_ORIGIN y +KCSAN_REPORT_VALUE_CHANGE_ONLY y +KCSAN_SELFTEST y +KCSAN_SKIP_WATCH 4000 +KCSAN_SKIP_WATCH_RANDOMIZE y +KCSAN_UDELAY_INTERRUPT 20 +KCSAN_UDELAY_TASK 80 I am seeing this data-races: root@iniza:~# LC_ALL=C dmesg -T | grep 'BUG: KCSAN: data-race' [Thu May 28 03:51:53 2020] BUG: KCSAN: data-race in mutex_spin_on_owner+0xe0/0x1b0 [Thu May 28 03:52:00 2020] BUG: KCSAN: data-race in mark_page_accessed / workingset_activation [Thu May 28 03:52:02 2020] BUG: KCSAN: data-race in mutex_spin_on_owner+0xe0/0x1b0 [Thu May 28 03:52:08 2020] BUG: KCSAN: data-race in blk_mq_sched_dispatch_requests / blk_mq_sched_dispatch_requests [Thu May 28 03:52:10 2020] BUG: KCSAN: data-race in dd_has_work / dd_insert_requests [Thu May 28 03:52:11 2020] BUG: KCSAN: data-race in mutex_spin_on_owner+0xe0/0x1b0 [Thu May 28 03:52:13 2020] BUG: KCSAN: data-race in page_counter_try_charge / page_counter_try_charge [Thu May 28 03:52:15 2020] BUG: KCSAN: data-race in ep_poll_callback / ep_send_events_proc [Thu May 28 03:52:21 2020] BUG: KCSAN: data-race in mutex_spin_on_owner+0xe0/0x1b0 [Thu May 28 03:52:25 2020] BUG: KCSAN: data-race in mutex_spin_on_owner+0xe0/0x1b0 [Thu May 28 03:52:26 2020] BUG: KCSAN: data-race in dd_has_work / deadline_remove_request [Thu May 28 03:52:31 2020] BUG: KCSAN: data-race in dd_has_work / deadline_remove_request [Thu May 28 03:52:38 2020] BUG: KCSAN: data-race in dd_has_work / deadline_remove_request [Thu May 28 03:52:53 2020] BUG: KCSAN: data-race in dd_has_work / dd_insert_requests [Thu May 28 03:52:56 2020] BUG: KCSAN: data-race in dd_has_work / deadline_remove_request [Thu May 28 03:52:59 2020] BUG: KCSAN: data-race in blk_mq_sched_dispatch_requests / blk_mq_sched_dispatch_requests [Thu May 28 03:53:25 2020] BUG: KCSAN: data-race in rwsem_spin_on_owner+0x102/0x1a0 [Thu May 28 03:53:25 2020] BUG: KCSAN: data-race in page_counter_try_charge / page_counter_try_charge [Thu May 28 03:53:39 2020] BUG: KCSAN: data-race in do_epoll_wait / ep_poll_callback [Thu May 28 03:53:39 2020] BUG: KCSAN: data-race in find_next_and_bit+0x30/0xd0 [Thu May 28 03:53:41 2020] BUG: KCSAN: data-race in dd_has_work / dd_insert_requests [Thu May 28 03:53:43 2020] BUG: KCSAN: data-race in do_epoll_wait / ep_poll_callback [Thu May 28 03:53:45 2020] BUG: KCSAN: data-race in dd_has_work / dd_insert_requests [Thu May 28 03:53:46 2020] BUG: KCSAN: data-race in blk_mq_sched_dispatch_requests / blk_mq_sched_dispatch_requests [Thu May 28 03:53:47 2020] BUG: KCSAN: data-race in rwsem_spin_on_owner+0x102/0x1a0 [Thu May 28 03:54:02 2020] BUG: KCSAN: data-race in dd_has_work / deadline_remove_request [Thu May 28 03:54:11 2020] BUG: KCSAN: data-race in find_next_and_bit+0x30/0xd0 [Thu May 28 03:54:19 2020] BUG: KCSAN: data-race in rwsem_spin_on_owner+0x102/0x1a0 [Thu May 28 03:55:00 2020] BUG: KCSAN: data-race in mutex_spin_on_owner+0xe0/0x1b0 [Thu May 28 03:56:14 2020] BUG: KCSAN: data-race in dd_has_work / deadline_remove_request [Thu May 28 03:56:50 2020] BUG: KCSAN: data-race in dd_has_work / deadline_remove_request [Thu May 28 03:56:50 2020] BUG: KCSAN: data-race in dd_has_work / deadline_remove_request [Thu May 28 03:56:52 2020] BUG: KCSAN: data-race in tick_nohz_next_event / tick_nohz_stop_tick [Thu May 28 03:56:58 2020] BUG: KCSAN: data-race in blk_mq_sched_dispatch_requests / blk_mq_sched_dispatch_requests [Thu May 28 03:57:58 2020] BUG: KCSAN: data-race in blk_mq_sched_dispatch_requests / blk_mq_sched_dispatch_requests [Thu May 28 03:58:00 2020] BUG: KCSAN: data-race in dd_has_work / deadline_remove_request [Thu May 28 03:58:07 2020] BUG: KCSAN: data-race in tick_nohz_next_event / tick_nohz_stop_tick [Thu May 28 03:58:44 2020] BUG: KCSAN: data-race in mutex_spin_on_owner+0xe0/0x1b0 [Thu May 28 03:58:49 2020] BUG: KCSAN: data-race in __bitmap_subset+0x38/0xd0 [Thu May 28 03:59:46 2020] BUG: KCSAN: data-race in tick_nohz_next_event / tick_nohz_stop_tick [Thu May 28 04:00:25 2020] BUG: KCSAN: data-race in dd_has_work / deadline_remove_request [Thu May 28 04:00:26 2020] BUG: KCSAN: data-race in tick_nohz_next_event / tick_nohz_stop_tick Full dmesg output and linux-config attached. - Sedat -