Hi Linus, This pull sits on top of of the core entry/exit and x86 entry branch from the tip tree, which contains the generic and x86 parts of this work. Here we convert the rest of the archs to support TIF_NOTIFY_SIGNAL. With that done, we can get rid of JOBCTL_TASK_WORK from task_work and signal.c, and also remove a deadlock work-around in io_uring around knowing that signal based task_work waking is invoked with the sighand wait queue head lock.
The motivation for this work is to decouple signal notify based task_work, of which io_uring is a heavy user of, from sighand. The sighand lock becomes a huge contention point, particularly for threaded workloads where it's shared between threads. Even outside of threaded applications it's slower than it needs to be. Roman Gershman <rom...@amazon.com> reported that his networked workload dropped from 1.6M QPS at 80% CPU to 1.0M QPS at 100% CPU after io_uring was changed to use TIF_NOTIFY_SIGNAL. The time was all spent hammering on the sighand lock, showing 57% of the CPU time there [1]. There are further cleanups possible on top of this. One example is TIF_PATCH_PENDING, where a patch already exists to use TIF_NOTIFY_SIGNAL instead. Hopefully this will also lead to more consolidation, but the work stands on its own as well. This throws a trivial merge conflict with arm64 since you pulled that, which is just a renumbering exercise and fiddling with _TIF_WORK_MASK in that same file (arch/arm64/include/asm/thread_info.h). [1] https://github.com/axboe/liburing/issues/215 Please pull! The following changes since commit f8394f232b1eab649ce2df5c5f15b0e528c92091: Linux 5.10-rc3 (2020-11-08 16:10:16 -0800) are available in the Git repository at: git://git.kernel.dk/linux-block.git tags/tif-task_work.arch-2020-12-14 for you to fetch changes up to 355fb9e2b78e78b38ec00f5cd9b05c6aceb98335: io_uring: remove 'twa_signal_ok' deadlock work-around (2020-12-12 09:17:38 -0700) ---------------------------------------------------------------- tif-task_work.arch-2020-12-14 ---------------------------------------------------------------- Jens Axboe (30): Merge tag 'core-entry-notify-signal' of git://git.kernel.org/.../tip/tip into tif-task_work.arch Merge branch 'x86/entry' of git://git.kernel.org/.../tip/tip into tif-task_work.arch arc: add support for TIF_NOTIFY_SIGNAL arm64: add support for TIF_NOTIFY_SIGNAL m68k: add support for TIF_NOTIFY_SIGNAL nios32: add support for TIF_NOTIFY_SIGNAL parisc: add support for TIF_NOTIFY_SIGNAL powerpc: add support for TIF_NOTIFY_SIGNAL mips: add support for TIF_NOTIFY_SIGNAL s390: add support for TIF_NOTIFY_SIGNAL um: add support for TIF_NOTIFY_SIGNAL sh: add support for TIF_NOTIFY_SIGNAL openrisc: add support for TIF_NOTIFY_SIGNAL csky: add support for TIF_NOTIFY_SIGNAL hexagon: add support for TIF_NOTIFY_SIGNAL microblaze: add support for TIF_NOTIFY_SIGNAL arm: add support for TIF_NOTIFY_SIGNAL xtensa: add support for TIF_NOTIFY_SIGNAL alpha: add support for TIF_NOTIFY_SIGNAL c6x: add support for TIF_NOTIFY_SIGNAL h8300: add support for TIF_NOTIFY_SIGNAL ia64: add support for TIF_NOTIFY_SIGNAL nds32: add support for TIF_NOTIFY_SIGNAL riscv: add support for TIF_NOTIFY_SIGNAL sparc: add support for TIF_NOTIFY_SIGNAL task_work: remove legacy TWA_SIGNAL path io_uring: JOBCTL_TASK_WORK is no longer used by task_work signal: kill JOBCTL_TASK_WORK kernel: remove checking for TIF_NOTIFY_SIGNAL io_uring: remove 'twa_signal_ok' deadlock work-around arch/alpha/include/asm/thread_info.h | 2 ++ arch/alpha/kernel/entry.S | 2 +- arch/alpha/kernel/signal.c | 2 +- arch/arc/include/asm/thread_info.h | 4 ++- arch/arc/kernel/entry.S | 3 ++- arch/arc/kernel/signal.c | 2 +- arch/arm/include/asm/thread_info.h | 7 +++++- arch/arm/kernel/entry-common.S | 6 ++--- arch/arm/kernel/entry-v7m.S | 2 +- arch/arm/kernel/signal.c | 2 +- arch/arm64/include/asm/thread_info.h | 5 +++- arch/arm64/kernel/signal.c | 2 +- arch/c6x/include/asm/thread_info.h | 1 + arch/c6x/kernel/asm-offsets.c | 1 + arch/c6x/kernel/signal.c | 3 ++- arch/csky/include/asm/thread_info.h | 5 +++- arch/csky/kernel/signal.c | 2 +- arch/h8300/include/asm/thread_info.h | 4 ++- arch/h8300/kernel/signal.c | 2 +- arch/hexagon/include/asm/thread_info.h | 2 ++ arch/hexagon/kernel/process.c | 2 +- arch/ia64/include/asm/thread_info.h | 4 ++- arch/ia64/kernel/process.c | 3 ++- arch/m68k/include/asm/thread_info.h | 1 + arch/m68k/kernel/signal.c | 3 ++- arch/microblaze/include/asm/thread_info.h | 2 ++ arch/microblaze/kernel/signal.c | 3 ++- arch/mips/include/asm/thread_info.h | 4 ++- arch/mips/kernel/signal.c | 2 +- arch/nds32/include/asm/thread_info.h | 2 ++ arch/nds32/kernel/ex-exit.S | 2 +- arch/nds32/kernel/signal.c | 2 +- arch/nios2/include/asm/thread_info.h | 2 ++ arch/nios2/kernel/signal.c | 3 ++- arch/openrisc/include/asm/thread_info.h | 2 ++ arch/openrisc/kernel/signal.c | 2 +- arch/parisc/include/asm/thread_info.h | 4 ++- arch/parisc/kernel/signal.c | 3 ++- arch/powerpc/include/asm/thread_info.h | 5 +++- arch/powerpc/kernel/signal.c | 2 +- arch/riscv/include/asm/thread_info.h | 5 +++- arch/riscv/kernel/signal.c | 2 +- arch/s390/include/asm/thread_info.h | 2 ++ arch/s390/kernel/entry.S | 11 +++++---- arch/s390/kernel/signal.c | 2 +- arch/sh/include/asm/thread_info.h | 4 ++- arch/sh/kernel/signal_32.c | 2 +- arch/sparc/include/asm/thread_info_32.h | 4 ++- arch/sparc/include/asm/thread_info_64.h | 6 +++-- arch/sparc/kernel/signal_32.c | 2 +- arch/sparc/kernel/signal_64.c | 2 +- arch/um/include/asm/thread_info.h | 2 ++ arch/um/kernel/process.c | 3 ++- arch/xtensa/include/asm/thread_info.h | 5 +++- arch/xtensa/kernel/entry.S | 4 +-- arch/xtensa/kernel/signal.c | 3 ++- fs/io_uring.c | 30 ++++++----------------- include/linux/entry-common.h | 4 --- include/linux/sched/jobctl.h | 4 +-- include/linux/sched/signal.h | 2 -- include/linux/tracehook.h | 4 --- kernel/signal.c | 22 ----------------- kernel/task_work.c | 30 +---------------------- 63 files changed, 128 insertions(+), 139 deletions(-) -- Jens Axboe
