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Date:   Wed, 16 Dec 2020 07:33:42 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: [GIT PULL] TIF_NOTIFY_SIGNAL for all archs

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 <romger@...zon.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

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