linux-stable/include/linux/rcutiny.h
Tejun Heo 969c79215a sched: replace migration_thread with cpu_stop
Currently migration_thread is serving three purposes - migration
pusher, context to execute active_load_balance() and forced context
switcher for expedited RCU synchronize_sched.  All three roles are
hardcoded into migration_thread() and determining which job is
scheduled is slightly messy.

This patch kills migration_thread and replaces all three uses with
cpu_stop.  The three different roles of migration_thread() are
splitted into three separate cpu_stop callbacks -
migration_cpu_stop(), active_load_balance_cpu_stop() and
synchronize_sched_expedited_cpu_stop() - and each use case now simply
asks cpu_stop to execute the callback as necessary.

synchronize_sched_expedited() was implemented with private
preallocated resources and custom multi-cpu queueing and waiting
logic, both of which are provided by cpu_stop.
synchronize_sched_expedited_count is made atomic and all other shared
resources along with the mutex are dropped.

synchronize_sched_expedited() also implemented a check to detect cases
where not all the callback got executed on their assigned cpus and
fall back to synchronize_sched().  If called with cpu hotplug blocked,
cpu_stop already guarantees that and the condition cannot happen;
otherwise, stop_machine() would break.  However, this patch preserves
the paranoid check using a cpumask to record on which cpus the stopper
ran so that it can serve as a bisection point if something actually
goes wrong theree.

Because the internal execution state is no longer visible,
rcu_expedited_torture_stats() is removed.

This patch also renames cpu_stop threads to from "stopper/%d" to
"migration/%d".  The names of these threads ultimately don't matter
and there's no reason to make unnecessary userland visible changes.

With this patch applied, stop_machine() and sched now share the same
resources.  stop_machine() is faster without wasting any resources and
sched migration users are much cleaner.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Dipankar Sarma <dipankar@in.ibm.com>
Cc: Josh Triplett <josh@freedesktop.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Dimitri Sivanich <sivanich@sgi.com>
2010-05-06 18:49:21 +02:00

115 lines
2.4 KiB
C

/*
* Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*
* Copyright IBM Corporation, 2008
*
* Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
*
* For detailed explanation of Read-Copy Update mechanism see -
* Documentation/RCU
*/
#ifndef __LINUX_TINY_H
#define __LINUX_TINY_H
#include <linux/cache.h>
void rcu_sched_qs(int cpu);
void rcu_bh_qs(int cpu);
#define __rcu_read_lock() preempt_disable()
#define __rcu_read_unlock() preempt_enable()
#define __rcu_read_lock_bh() local_bh_disable()
#define __rcu_read_unlock_bh() local_bh_enable()
#define call_rcu_sched call_rcu
#define rcu_init_sched() do { } while (0)
extern void rcu_check_callbacks(int cpu, int user);
static inline int rcu_needs_cpu(int cpu)
{
return 0;
}
/*
* Return the number of grace periods.
*/
static inline long rcu_batches_completed(void)
{
return 0;
}
/*
* Return the number of bottom-half grace periods.
*/
static inline long rcu_batches_completed_bh(void)
{
return 0;
}
static inline void rcu_force_quiescent_state(void)
{
}
static inline void rcu_bh_force_quiescent_state(void)
{
}
static inline void rcu_sched_force_quiescent_state(void)
{
}
#define synchronize_rcu synchronize_sched
static inline void synchronize_rcu_expedited(void)
{
synchronize_sched();
}
static inline void synchronize_rcu_bh_expedited(void)
{
synchronize_sched();
}
struct notifier_block;
#ifdef CONFIG_NO_HZ
extern void rcu_enter_nohz(void);
extern void rcu_exit_nohz(void);
#else /* #ifdef CONFIG_NO_HZ */
static inline void rcu_enter_nohz(void)
{
}
static inline void rcu_exit_nohz(void)
{
}
#endif /* #else #ifdef CONFIG_NO_HZ */
static inline void exit_rcu(void)
{
}
static inline int rcu_preempt_depth(void)
{
return 0;
}
#endif /* __LINUX_RCUTINY_H */