Re: [PATCH] rcu: make PREEMPT_RCU to be a decoration of TREE_RCU

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On 2019/10/15 10:45 上午, Lai Jiangshan wrote:


On 2019/10/15 10:00 上午, Paul E. McKenney wrote:
On Tue, Oct 15, 2019 at 09:50:21AM +0800, Lai Jiangshan wrote:
On Tue, Oct 15, 2019 at 9:46 AM Paul E. McKenney <paulmck@xxxxxxxxxx> wrote:

On Mon, Oct 14, 2019 at 02:48:32PM -0400, Joel Fernandes wrote:
On Sun, Oct 13, 2019 at 12:59:57PM +0000, Lai Jiangshan wrote:
Currently PREEMPT_RCU and TREE_RCU are "contrary" configs
when they can't be both on. But PREEMPT_RCU is actually a kind
of TREE_RCU in the implementation. It seams to be appropriate
to make PREEMPT_RCU to be a decorative option of TREE_RCU.


Looks like a nice simplification and so far I could not poke any holes in the
code...

I am in support of this patch for further review and testing. Thanks!

Reviewed-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>

Thank you both!

Lai, what is this patch against?  It does not want to apply to the current
-rcu "dev" branch.

Oh, sorry

I wrongly made the change base on upstream.
I will rebase later.

Very good, looking forward to this updated version.

                            Thanx, Paul


In my box, the patch can be applied to the -rcu "dev" well.

Oh, I first applied it by "git cherry-pick" not "git am".
It did have conflicts when using "git am". Updated patch
was sent, sorry for the nosing.

thanks
Lai


And there is nothing strange after boot.

Have I just made a mistake a again? In my box, the HEAD
of -rcu "dev" is 9725023b ("torture: Handle jitter for CPUs that cannot be offlined")

Thanks
Lai


thanks
Lai


                                                         Thanx, Paul

thanks,

  - Joel


Signed-off-by: Lai Jiangshan <jiangshanlai@xxxxxxxxx>
Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>
---
  include/linux/rcupdate.h   |  4 ++--
  include/trace/events/rcu.h |  4 ++--
  kernel/rcu/Kconfig         | 13 +++++++------
  kernel/rcu/Makefile        |  1 -
  kernel/rcu/rcu.h           |  2 +-
  kernel/rcu/update.c        |  2 +-
  kernel/sysctl.c            |  2 +-
  7 files changed, 14 insertions(+), 14 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 75a2eded7aa2..1eee9f6c27f9 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -167,7 +167,7 @@ do { \
   * TREE_RCU and rcu_barrier_() primitives in TINY_RCU.
   */

-#if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
+#if defined(CONFIG_TREE_RCU)
  #include <linux/rcutree.h>
  #elif defined(CONFIG_TINY_RCU)
  #include <linux/rcutiny.h>
@@ -583,7 +583,7 @@ do { \    * read-side critical section that would block in a !PREEMPT kernel.
   * But if you want the full story, read on!
   *
- * In non-preemptible RCU implementations (TREE_RCU and TINY_RCU),
+ * In non-preemptible RCU implementations (pure TREE_RCU and TINY_RCU),    * it is illegal to block while in an RCU read-side critical section.    * In preemptible RCU implementations (PREEMPT_RCU) in CONFIG_PREEMPTION
   * kernel builds, RCU read-side critical sections may be preempted,
diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
index 694bd040cf51..1ce15c5be4c8 100644
--- a/include/trace/events/rcu.h
+++ b/include/trace/events/rcu.h
@@ -41,7 +41,7 @@ TRACE_EVENT(rcu_utilization,
     TP_printk("%s", __entry->s)
  );

-#if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
+#if defined(CONFIG_TREE_RCU)

  /*
   * Tracepoint for grace-period events.  Takes a string identifying the
@@ -425,7 +425,7 @@ TRACE_EVENT_RCU(rcu_fqs,
               __entry->cpu, __entry->qsevent)
  );

-#endif /* #if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU) */
+#endif /* #if defined(CONFIG_TREE_RCU) */

  /*
   * Tracepoint for dyntick-idle entry/exit events.  These take a string
diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig
index 7644eda17d62..0303934e6ef0 100644
--- a/kernel/rcu/Kconfig
+++ b/kernel/rcu/Kconfig
@@ -7,7 +7,7 @@ menu "RCU Subsystem"

  config TREE_RCU
     bool
-   default y if !PREEMPTION && SMP
+   default y if SMP
     help
       This option selects the RCU implementation that is
       designed for very large SMP system with hundreds or
@@ -17,6 +17,7 @@ config TREE_RCU
  config PREEMPT_RCU
     bool
     default y if PREEMPTION
+   select TREE_RCU
     help
       This option selects the RCU implementation that is
       designed for very large SMP systems with hundreds or
@@ -78,7 +79,7 @@ config TASKS_RCU
       user-mode execution as quiescent states.

  config RCU_STALL_COMMON
-   def_bool ( TREE_RCU || PREEMPT_RCU )
+   def_bool TREE_RCU
     help
       This option enables RCU CPU stall code that is common between
       the TINY and TREE variants of RCU.  The purpose is to allow
@@ -86,13 +87,13 @@ config RCU_STALL_COMMON
       making these warnings mandatory for the tree variants.

  config RCU_NEED_SEGCBLIST
-   def_bool ( TREE_RCU || PREEMPT_RCU || TREE_SRCU )
+   def_bool ( TREE_RCU || TREE_SRCU )

  config RCU_FANOUT
     int "Tree-based hierarchical RCU fanout value"
     range 2 64 if 64BIT
     range 2 32 if !64BIT
-   depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT
+   depends on TREE_RCU && RCU_EXPERT
     default 64 if 64BIT
     default 32 if !64BIT
     help
@@ -112,7 +113,7 @@ config RCU_FANOUT_LEAF
     int "Tree-based hierarchical RCU leaf-level fanout value"
     range 2 64 if 64BIT
     range 2 32 if !64BIT
-   depends on (TREE_RCU || PREEMPT_RCU) && RCU_EXPERT
+   depends on TREE_RCU && RCU_EXPERT
     default 16
     help
       This option controls the leaf-level fanout of hierarchical
@@ -187,7 +188,7 @@ config RCU_BOOST_DELAY

  config RCU_NOCB_CPU
     bool "Offload RCU callback processing from boot-selected CPUs"
-   depends on TREE_RCU || PREEMPT_RCU
+   depends on TREE_RCU
     depends on RCU_EXPERT || NO_HZ_FULL
     default n
     help
diff --git a/kernel/rcu/Makefile b/kernel/rcu/Makefile
index 020e8b6a644b..82d5fba48b2f 100644
--- a/kernel/rcu/Makefile
+++ b/kernel/rcu/Makefile
@@ -9,6 +9,5 @@ obj-$(CONFIG_TINY_SRCU) += srcutiny.o
  obj-$(CONFIG_RCU_TORTURE_TEST) += rcutorture.o
  obj-$(CONFIG_RCU_PERF_TEST) += rcuperf.o
  obj-$(CONFIG_TREE_RCU) += tree.o
-obj-$(CONFIG_PREEMPT_RCU) += tree.o
  obj-$(CONFIG_TINY_RCU) += tiny.o
  obj-$(CONFIG_RCU_NEED_SEGCBLIST) += rcu_segcblist.o
diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 8fd4f82c9b3d..4149ba76824f 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -452,7 +452,7 @@ enum rcutorture_type {
     INVALID_RCU_FLAVOR
  };

-#if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
+#if defined(CONFIG_TREE_RCU)
  void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
                         unsigned long *gp_seq);
  void rcutorture_record_progress(unsigned long vernum);
diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
index 1861103662db..34a7452b25fd 100644
--- a/kernel/rcu/update.c
+++ b/kernel/rcu/update.c
@@ -435,7 +435,7 @@ struct debug_obj_descr rcuhead_debug_descr = {
  EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
  #endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */

-#if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE)
+#if defined(CONFIG_TREE_RCU) || defined(CONFIG_RCU_TRACE)
  void do_trace_rcu_torture_read(const char *rcutorturename, struct rcu_head *rhp,
                            unsigned long secs,
                            unsigned long c_old, unsigned long c)
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 00fcea236eba..2ace158a4d72 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1268,7 +1268,7 @@ static struct ctl_table kern_table[] = {
             .proc_handler   = proc_do_static_key,
     },
  #endif
-#if defined(CONFIG_TREE_RCU) || defined(CONFIG_PREEMPT_RCU)
+#if defined(CONFIG_TREE_RCU)
     {
             .procname       = "panic_on_rcu_stall",
             .data           = &sysctl_panic_on_rcu_stall,
--
2.20.1




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