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* [PATCH V2 0/7] rcu: introduce percpu rcu_preempt_depth
@ 2019-11-02 12:45 Lai Jiangshan
  2019-11-02 12:45 ` [PATCH V2 1/7] rcu: use preempt_count to test whether scheduler locks is held Lai Jiangshan
                   ` (7 more replies)
  0 siblings, 8 replies; 39+ messages in thread
From: Lai Jiangshan @ 2019-11-02 12:45 UTC (permalink / raw)
  To: linux-kernel
  Cc: Lai Jiangshan, Paul E. McKenney, Josh Triplett, Steven Rostedt,
	Mathieu Desnoyers, Lai Jiangshan, Joel Fernandes, rcu

Rather than using the generic version of preempt_count, x86 uses
a special version of preempt_count implementation that take advantage
of x86 (single instruction to access/add/decl/flip-bits of percpu
counter). It makes the preempt_count operations really cheap.

For x86, rcu_preempt_depth can also take the same advantage by
using the same technique.

After the patchset:
 - No function call when using rcu_read_[un]lock().
     It is minor improvement, other arch can also achieve it via
     moving ->rcu_read_lock_nesting and ->rcu_read_unlock_special
     to thread_info, but inlined rcu_read_[un]lock() generates
     more instructions and footprint in other arch generally.
 - Only single instruction for rcu_read_lock().
 - Only 2 instructions for the fast path of rcu_read_unlock().

Patch4 simplifies rcu_read_unlock() by avoid using negative
->rcu_read_lock_nesting, Patch7 introduces the percpu rcu_preempt_depth.
Other patches are for preparation.

changed from v1:
  drop patch1/2 of the v1
  drop merged patches

  Using special.b.deferred_qs to avoid wakeup in v1 is changed to using
  preempt_count. And special.b.deferred_qs is removed.

Lai Jiangshan (7):
  rcu: use preempt_count to test whether scheduler locks is held
  rcu: cleanup rcu_preempt_deferred_qs()
  rcu: remove useless special.b.deferred_qs
  rcu: don't use negative ->rcu_read_lock_nesting
  rcu: wrap usages of rcu_read_lock_nesting
  rcu: clear the special.b.need_qs in rcu_note_context_switch()
  x86,rcu: use percpu rcu_preempt_depth

 arch/x86/Kconfig                         |   2 +
 arch/x86/include/asm/rcu_preempt_depth.h |  87 +++++++++++++++++++
 arch/x86/kernel/cpu/common.c             |   7 ++
 arch/x86/kernel/process_32.c             |   2 +
 arch/x86/kernel/process_64.c             |   2 +
 include/linux/rcupdate.h                 |  24 ++++++
 include/linux/sched.h                    |   2 +-
 init/init_task.c                         |   2 +-
 kernel/fork.c                            |   2 +-
 kernel/rcu/Kconfig                       |   3 +
 kernel/rcu/tree_exp.h                    |  35 ++------
 kernel/rcu/tree_plugin.h                 | 101 ++++++++++++++---------
 12 files changed, 196 insertions(+), 73 deletions(-)
 create mode 100644 arch/x86/include/asm/rcu_preempt_depth.h

-- 
2.20.1


^ permalink raw reply	[flat|nested] 39+ messages in thread

end of thread, other threads:[~2020-02-19  3:59 UTC | newest]

Thread overview: 39+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-11-02 12:45 [PATCH V2 0/7] rcu: introduce percpu rcu_preempt_depth Lai Jiangshan
2019-11-02 12:45 ` [PATCH V2 1/7] rcu: use preempt_count to test whether scheduler locks is held Lai Jiangshan
2019-11-15 16:53   ` Paul E. McKenney
2020-02-19  3:31   ` Joel Fernandes
2020-02-19  3:59     ` Paul E. McKenney
2019-11-02 12:45 ` [PATCH V2 2/7] rcu: cleanup rcu_preempt_deferred_qs() Lai Jiangshan
2019-11-03  2:01   ` Boqun Feng
2019-11-03  5:01     ` Lai Jiangshan
2019-11-04 14:55       ` Paul E. McKenney
2019-11-05  2:09         ` Lai Jiangshan
2019-11-05  7:19           ` Paul E. McKenney
2019-11-11 14:32             ` Paul E. McKenney
2019-11-12  1:28               ` Lai Jiangshan
2020-02-17 23:23                 ` Paul E. McKenney
2020-02-18 14:41                   ` Steven Rostedt
2020-02-18 16:43                     ` Paul E. McKenney
2019-11-15 16:55   ` Paul E. McKenney
2019-11-02 12:45 ` [PATCH V2 3/7] rcu: remove useless special.b.deferred_qs Lai Jiangshan
2020-02-17 23:23   ` Paul E. McKenney
2019-11-02 12:45 ` [PATCH V2 4/7] rcu: don't use negative ->rcu_read_lock_nesting Lai Jiangshan
2020-02-17 23:26   ` Paul E. McKenney
2019-11-02 12:45 ` [PATCH V2 5/7] rcu: wrap usages of rcu_read_lock_nesting Lai Jiangshan
2019-11-15 22:25   ` Paul E. McKenney
2019-11-02 12:45 ` [PATCH V2 6/7] rcu: clear the special.b.need_qs in rcu_note_context_switch() Lai Jiangshan
2019-11-16 15:46   ` Paul E. McKenney
2019-11-02 12:45 ` [PATCH V2 7/7] x86,rcu: use percpu rcu_preempt_depth Lai Jiangshan
2019-11-02 16:30   ` Borislav Petkov
2019-11-03  4:33     ` Lai Jiangshan
2019-11-04  9:25   ` Sebastian Andrzej Siewior
2019-11-04 11:41     ` Lai Jiangshan
2019-11-04 12:09       ` Sebastian Andrzej Siewior
2019-11-16 15:48   ` Paul E. McKenney
2019-11-18  2:02     ` Lai Jiangshan
2019-11-18 14:59       ` Paul E. McKenney
2019-11-19  1:59         ` Lai Jiangshan
2019-11-19 21:14           ` Paul E. McKenney
2019-11-20  2:47             ` Lai Jiangshan
2019-11-21  4:02               ` Paul E. McKenney
2019-11-02 15:05 ` [PATCH V2 0/7] rcu: introduce " Paul E. McKenney

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