This mixes up the RCU dynticks counter and the context tracking state
updates into a single atomic instruction. This may serve several
purposes:

1) Improve CPU isolation with deferring some disturbances until sensitive
   userspace workload completes and goes to the kernel. This can take
   several forms, for example smp_call_function_housekeeping() or
   on_each_housekeeping_cpu() to enqueue and execute work on all
   housekeeping CPUs. Then an atomic operation on ct->state can defer
   the work on nohz_full CPUs until they run in kernel (or IPI them
   if they are in kernel mode), see this proposal by Peter:
   https://lore.kernel.org/all/20210929151723.162004989@infradead.org/#r

2) Unearth sysidle (https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git/commit/?h=sysidle.2017.05.11a&id=fe5ac724d81a3c7803e60c2232718f212f3f38d4)
   This feature allowed to shutdown the tick on the last housekeeping
   CPU once the rest of the system is fully idle. We needed some proper
   fully ordered context tracking for that.

Inspired by Peterz: https://lore.kernel.org/all/20210929151723.162004989@infradead.org

git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
	rcu/context-tracking

HEAD: e4eaff86ec91c1cbde9a113cf5232dac9f897337

Thanks,
	Frederic
---

Frederic Weisbecker (19):
      context_tracking: Rename __context_tracking_enter/exit() to __ct_user_enter/exit()
      context_tracking: Rename context_tracking_user_enter/exit() to user_enter/exit_callable()
      context_tracking: Rename context_tracking_enter/exit() to ct_user_enter/exit()
      context_tracking: Rename context_tracking_cpu_set() to context_tracking_cpu_track_user()
      context_tracking: Split user tracking Kconfig
      context_tracking: Take idle eqs entrypoints over RCU
      context_tracking: Take IRQ eqs entrypoints over RCU
      context_tracking: Take NMI eqs entrypoints over RCU
      rcu/context-tracking: Remove rcu_irq_enter/exit()
      rcu/context_tracking: Move dynticks counter to context tracking
      rcu/context_tracking: Move dynticks_nesting to context tracking
      rcu/context_tracking: Move dynticks_nmi_nesting to context tracking
      rcu/context-tracking: Move deferred nocb resched to context tracking
      rcu/context-tracking: Move RCU-dynticks internal functions to context_tracking
      rcu/context-tracking: Remove unused and/or unecessary middle functions
      context_tracking: Convert state to atomic_t
      rcu/context-tracking: Use accessor for dynticks counter value
      rcu/context_tracking: Merge dynticks counter and context tracking states
      context_tracking: Exempt CONFIG_HAVE_CONTEXT_TRACKING_USER_OFFSTACK from non-active tracking


 .../RCU/Design/Requirements/Requirements.rst       |  10 +-
 Documentation/RCU/stallwarn.rst                    |   6 +-
 .../time/context-tracking/arch-support.txt         |   6 +-
 arch/Kconfig                                       |   8 +-
 arch/arm/Kconfig                                   |   2 +-
 arch/arm/kernel/entry-common.S                     |   4 +-
 arch/arm/kernel/entry-header.S                     |  12 +-
 arch/arm/mach-imx/cpuidle-imx6q.c                  |   5 +-
 arch/arm64/Kconfig                                 |   2 +-
 arch/arm64/kernel/entry-common.c                   |  14 +-
 arch/csky/Kconfig                                  |   2 +-
 arch/csky/kernel/entry.S                           |   8 +-
 arch/mips/Kconfig                                  |   2 +-
 arch/powerpc/Kconfig                               |   2 +-
 arch/powerpc/include/asm/context_tracking.h        |   2 +-
 arch/riscv/Kconfig                                 |   2 +-
 arch/riscv/kernel/entry.S                          |  12 +-
 arch/sparc/Kconfig                                 |   2 +-
 arch/sparc/kernel/rtrap_64.S                       |   2 +-
 arch/x86/Kconfig                                   |   4 +-
 arch/x86/mm/fault.c                                |   2 +-
 drivers/acpi/processor_idle.c                      |   5 +-
 drivers/cpuidle/cpuidle-psci.c                     |   8 +-
 drivers/cpuidle/cpuidle.c                          |   9 +-
 include/linux/context_tracking.h                   |  81 ++--
 include/linux/context_tracking_irq.h               |  21 +
 include/linux/context_tracking_state.h             |  92 +++-
 include/linux/entry-common.h                       |  10 +-
 include/linux/hardirq.h                            |  12 +-
 include/linux/rcupdate.h                           |   7 +-
 include/linux/rcutiny.h                            |   6 -
 include/linux/rcutree.h                            |  15 +-
 include/linux/tracepoint.h                         |   4 +-
 init/Kconfig                                       |   4 +-
 kernel/context_tracking.c                          | 526 +++++++++++++++++++--
 kernel/cpu_pm.c                                    |   8 +-
 kernel/entry/common.c                              |  16 +-
 kernel/extable.c                                   |   4 +-
 kernel/locking/lockdep.c                           |   2 +-
 kernel/rcu/Kconfig                                 |   2 +
 kernel/rcu/rcu.h                                   |   4 -
 kernel/rcu/tree.c                                  | 478 ++-----------------
 kernel/rcu/tree.h                                  |   8 -
 kernel/rcu/tree_exp.h                              |   2 +-
 kernel/rcu/tree_plugin.h                           |  36 +-
 kernel/rcu/tree_stall.h                            |   7 +-
 kernel/rcu/update.c                                |   2 +-
 kernel/sched/core.c                                |   2 +-
 kernel/sched/idle.c                                |  11 +-
 kernel/softirq.c                                   |   4 +-
 kernel/time/Kconfig                                |  22 +-
 kernel/time/tick-sched.c                           |   2 +-
 kernel/trace/trace.c                               |   8 +-
 53 files changed, 793 insertions(+), 734 deletions(-)

On Wed, 2022-03-02 at 16:47 +0100, Frederic Weisbecker wrote:
> This mixes up the RCU dynticks counter and the context tracking state
> updates into a single atomic instruction. This may serve several
> purposes:
> 
> 1) Improve CPU isolation with deferring some disturbances until sensitive
>    userspace workload completes and goes to the kernel. This can take
>    several forms, for example smp_call_function_housekeeping() or
>    on_each_housekeeping_cpu() to enqueue and execute work on all
>    housekeeping CPUs. Then an atomic operation on ct->state can defer
>    the work on nohz_full CPUs until they run in kernel (or IPI them
>    if they are in kernel mode), see this proposal by Peter:
>    https://lore.kernel.org/all/20210929151723.162004989@infradead.org/#r
> 
> 2) Unearth sysidle (https://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git/commit/?h=sysidle.2017.05.11a&id=fe5ac724d81a3c7803e60c2232718f212f3f38d4)
>    This feature allowed to shutdown the tick on the last housekeeping
>    CPU once the rest of the system is fully idle. We needed some proper
>    fully ordered context tracking for that.
> 
> Inspired by Peterz: https://lore.kernel.org/all/20210929151723.162004989@infradead.org
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
> 	rcu/context-tracking
> 
> HEAD: e4eaff86ec91c1cbde9a113cf5232dac9f897337
> 
> Thanks,
> 	Frederic
> ---

I've been testing patches 1 to 18 on my nohz_full setup. Everything is looking
good so far.

Regards,
Nicolas