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Date: Mon, 22 Sep 2014 09:44:58 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Josh Triplett <josh@...htriplett.org>
Cc: Pranith Kumar <bobby.prani@...il.com>,
Steven Rostedt <rostedt@...dmis.org>,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Lai Jiangshan <laijs@...fujitsu.com>,
open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] rcu: Remove redundant CONFIG_PREEMPT_RCU option
On Mon, Sep 22, 2014 at 09:25:34AM -0700, Josh Triplett wrote:
> On Sun, Sep 21, 2014 at 12:49:54PM -0400, Pranith Kumar wrote:
> > PREEMPT_RCU and TREE_PREEMPT_RCU serve the same function after TINY_PREEMPT_RCU
> > has been removed. This patch removes CONFIG_PREEMPT_RCU and uses
> > CONFIG_TREE_PREEMPT_RCU in its place.
> >
> > Signed-off-by: Pranith Kumar <bobby.prani@...il.com>
>
> I think it would actually make more sense to do this the other way
> around, if at all: drop TREE_PREEMPT_RCU in favor of PREEMPT_RCU. The
> instances shown here don't care about *which* preemptible RCU
> implementation the kernel uses, they just need to behave differently
> when preemptible. Let's also not assume that no new RCU implementation
> will ever arise superceding TREE_PREEMPT_RCU.
Given that there has thus far been no fewer than three distinct
implementations of PREEMPT_RCU (one in -rt, the first in mainline, and the
current one in mainline), it would indeed be quite wise to avoid assuming
that there never will be some new PREEMPT_RCU implementation. ;-)
Thanx, Paul
> - Josh Triplett
>
> > arch/xtensa/configs/s6105_defconfig | 2 +-
> > include/linux/init_task.h | 2 +-
> > include/linux/rcupdate.h | 16 ++++++++--------
> > include/linux/sched.h | 10 +++++-----
> > init/Kconfig | 6 ------
> > kernel/rcu/update.c | 4 ++--
> > tools/testing/selftests/rcutorture/doc/TINY_RCU.txt | 2 +-
> > .../selftests/rcutorture/doc/TREE_RCU-kconfig.txt | 2 +-
> > 8 files changed, 19 insertions(+), 25 deletions(-)
> >
> > diff --git a/arch/xtensa/configs/s6105_defconfig b/arch/xtensa/configs/s6105_defconfig
> > index 12a492a..dab1a99 100644
> > --- a/arch/xtensa/configs/s6105_defconfig
> > +++ b/arch/xtensa/configs/s6105_defconfig
> > @@ -35,7 +35,7 @@ CONFIG_SYSVIPC_SYSCTL=y
> > #
> > # CONFIG_CLASSIC_RCU is not set
> > # CONFIG_TREE_RCU is not set
> > -CONFIG_PREEMPT_RCU=y
> > +CONFIG_TREE_PREEMPT_RCU=y
> > # CONFIG_RCU_TRACE is not set
> > # CONFIG_TREE_RCU_TRACE is not set
> > # CONFIG_PREEMPT_RCU_TRACE is not set
> > diff --git a/include/linux/init_task.h b/include/linux/init_task.h
> > index 77fc43f..39600f4 100644
> > --- a/include/linux/init_task.h
> > +++ b/include/linux/init_task.h
> > @@ -108,7 +108,7 @@ extern struct group_info init_groups;
> > #else
> > #define INIT_TASK_RCU_TREE_PREEMPT(tsk)
> > #endif
> > -#ifdef CONFIG_PREEMPT_RCU
> > +#ifdef CONFIG_TREE_PREEMPT_RCU
> > #define INIT_TASK_RCU_PREEMPT(tsk) \
> > .rcu_read_lock_nesting = 0, \
> > .rcu_read_unlock_special.s = 0, \
> > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> > index a4a819f..17a15d5 100644
> > --- a/include/linux/rcupdate.h
> > +++ b/include/linux/rcupdate.h
> > @@ -103,7 +103,7 @@ void do_trace_rcu_torture_read(const char *rcutorturename,
> >
> > /* Exported common interfaces */
> >
> > -#ifdef CONFIG_PREEMPT_RCU
> > +#ifdef CONFIG_TREE_PREEMPT_RCU
> >
> > /**
> > * call_rcu() - Queue an RCU callback for invocation after a grace period.
> > @@ -140,12 +140,12 @@ void do_trace_rcu_torture_read(const char *rcutorturename,
> > void call_rcu(struct rcu_head *head,
> > void (*func)(struct rcu_head *head));
> >
> > -#else /* #ifdef CONFIG_PREEMPT_RCU */
> > +#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
> >
> > /* In classic RCU, call_rcu() is just call_rcu_sched(). */
> > #define call_rcu call_rcu_sched
> >
> > -#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
> > +#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
> >
> > /**
> > * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period.
> > @@ -217,7 +217,7 @@ void call_rcu_tasks(struct rcu_head *head, void (*func)(struct rcu_head *head));
> > void synchronize_rcu_tasks(void);
> > void rcu_barrier_tasks(void);
> >
> > -#ifdef CONFIG_PREEMPT_RCU
> > +#ifdef CONFIG_TREE_PREEMPT_RCU
> >
> > void __rcu_read_lock(void);
> > void __rcu_read_unlock(void);
> > @@ -227,12 +227,12 @@ void synchronize_rcu(void);
> > /*
> > * Defined as a macro as it is a very low level header included from
> > * areas that don't even know about current. This gives the rcu_read_lock()
> > - * nesting depth, but makes sense only if CONFIG_PREEMPT_RCU -- in other
> > + * nesting depth, but makes sense only if CONFIG_TREE_PREEMPT_RCU -- in other
> > * types of kernel builds, the rcu_read_lock() nesting depth is unknowable.
> > */
> > #define rcu_preempt_depth() (current->rcu_read_lock_nesting)
> >
> > -#else /* #ifdef CONFIG_PREEMPT_RCU */
> > +#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
> >
> > static inline void __rcu_read_lock(void)
> > {
> > @@ -254,7 +254,7 @@ static inline int rcu_preempt_depth(void)
> > return 0;
> > }
> >
> > -#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
> > +#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
> >
> > /* Internal to kernel */
> > void rcu_init(void);
> > @@ -530,7 +530,7 @@ static inline int rcu_read_lock_sched_held(void)
> > } \
> > } while (0)
> >
> > -#if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_PREEMPT_RCU)
> > +#if defined(CONFIG_PROVE_RCU) && !defined(CONFIG_TREE_PREEMPT_RCU)
> > static inline void rcu_preempt_sleep_check(void)
> > {
> > rcu_lockdep_assert(!lock_is_held(&rcu_lock_map),
> > diff --git a/include/linux/sched.h b/include/linux/sched.h
> > index 42888d7..6acaa30 100644
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -1269,11 +1269,11 @@ struct task_struct {
> > int nr_cpus_allowed;
> > cpumask_t cpus_allowed;
> >
> > -#ifdef CONFIG_PREEMPT_RCU
> > +#ifdef CONFIG_TREE_PREEMPT_RCU
> > int rcu_read_lock_nesting;
> > union rcu_special rcu_read_unlock_special;
> > struct list_head rcu_node_entry;
> > -#endif /* #ifdef CONFIG_PREEMPT_RCU */
> > +#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
> > #ifdef CONFIG_TREE_PREEMPT_RCU
> > struct rcu_node *rcu_blocked_node;
> > #endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
> > @@ -2014,12 +2014,12 @@ extern void task_clear_jobctl_pending(struct task_struct *task,
> >
> > static inline void rcu_copy_process(struct task_struct *p)
> > {
> > -#ifdef CONFIG_PREEMPT_RCU
> > +#ifdef CONFIG_TREE_PREEMPT_RCU
> > p->rcu_read_lock_nesting = 0;
> > p->rcu_read_unlock_special.s = 0;
> > p->rcu_blocked_node = NULL;
> > INIT_LIST_HEAD(&p->rcu_node_entry);
> > -#endif /* #ifdef CONFIG_PREEMPT_RCU */
> > +#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
> > #ifdef CONFIG_TASKS_RCU
> > p->rcu_tasks_holdout = false;
> > INIT_LIST_HEAD(&p->rcu_tasks_holdout_list);
> > @@ -2752,7 +2752,7 @@ extern int __cond_resched_softirq(void);
> >
> > static inline void cond_resched_rcu(void)
> > {
> > -#if defined(CONFIG_DEBUG_ATOMIC_SLEEP) || !defined(CONFIG_PREEMPT_RCU)
> > +#if defined(CONFIG_DEBUG_ATOMIC_SLEEP) || !defined(CONFIG_TREE_PREEMPT_RCU)
> > rcu_read_unlock();
> > cond_resched();
> > rcu_read_lock();
> > diff --git a/init/Kconfig b/init/Kconfig
> > index 8a2b97c..27ad03c 100644
> > --- a/init/Kconfig
> > +++ b/init/Kconfig
> > @@ -501,12 +501,6 @@ config TINY_RCU
> >
> > endchoice
> >
> > -config PREEMPT_RCU
> > - def_bool TREE_PREEMPT_RCU
> > - help
> > - This option enables preemptible-RCU code that is common between
> > - TREE_PREEMPT_RCU and, in the old days, TINY_PREEMPT_RCU.
> > -
> > config TASKS_RCU
> > bool "Task_based RCU implementation using voluntary context switch"
> > default n
> > diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
> > index 3ef8ba5..8848a32 100644
> > --- a/kernel/rcu/update.c
> > +++ b/kernel/rcu/update.c
> > @@ -62,7 +62,7 @@ MODULE_ALIAS("rcupdate");
> >
> > module_param(rcu_expedited, int, 0);
> >
> > -#ifdef CONFIG_PREEMPT_RCU
> > +#ifdef CONFIG_TREE_PREEMPT_RCU
> >
> > /*
> > * Preemptible RCU implementation for rcu_read_lock().
> > @@ -108,7 +108,7 @@ void __rcu_read_unlock(void)
> > }
> > EXPORT_SYMBOL_GPL(__rcu_read_unlock);
> >
> > -#endif /* #ifdef CONFIG_PREEMPT_RCU */
> > +#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
> >
> > #ifdef CONFIG_DEBUG_LOCK_ALLOC
> > static struct lock_class_key rcu_lock_key;
> > diff --git a/tools/testing/selftests/rcutorture/doc/TINY_RCU.txt b/tools/testing/selftests/rcutorture/doc/TINY_RCU.txt
> > index 28db67b..4fea92d 100644
> > --- a/tools/testing/selftests/rcutorture/doc/TINY_RCU.txt
> > +++ b/tools/testing/selftests/rcutorture/doc/TINY_RCU.txt
> > @@ -31,7 +31,7 @@ CONFIG_RCU_TORTURE_TEST
> >
> > CONFIG_HOTPLUG_CPU
> > CONFIG_PREEMPT
> > -CONFIG_PREEMPT_RCU
> > +CONFIG_TREE_PREEMPT_RCU
> > CONFIG_SMP
> > CONFIG_TINY_RCU
> > CONFIG_TREE_PREEMPT_RCU
> > diff --git a/tools/testing/selftests/rcutorture/doc/TREE_RCU-kconfig.txt b/tools/testing/selftests/rcutorture/doc/TREE_RCU-kconfig.txt
> > index f85c45e..081dece 100644
> > --- a/tools/testing/selftests/rcutorture/doc/TREE_RCU-kconfig.txt
> > +++ b/tools/testing/selftests/rcutorture/doc/TREE_RCU-kconfig.txt
> > @@ -62,7 +62,7 @@ CONFIG_NO_HZ_FULL_SYSIDLE_SMALL
> > Defer until Frederic uses this.
> >
> > CONFIG_PREEMPT_COUNT
> > -CONFIG_PREEMPT_RCU
> > +CONFIG_TREE_PREEMPT_RCU
> >
> > Redundant with CONFIG_PREEMPT, ignore.
> >
> > --
> > 2.1.0
> >
>
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