Messages in this thread | | | Date | Tue, 19 Oct 2010 10:06:45 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH 1/2] rcu,cleanup: move synchronize_sched_expedited() out of sched.c |
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On Tue, Oct 19, 2010 at 03:56:56PM +0800, Lai Jiangshan wrote: > > The first version of synchronize_sched_expedited() use the migration code > of the scheduler code, so it have to be implemented in sched.c > > but now, the synchronize_sched_expedited() does not use such code, > it is time to move it out of sched.c. > > Different rcu implementation' synchronize_sched_expedited() are also > different. so we move synchronize_sched_expedited() to kernel/rcu{tree,tiny}_plugin.h > instead of kerenl/rcupdate.c
Good stuff, Lai!!!
Please see below for one small but important comment.
Thanx, Paul
> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> > --- > rcutiny_plugin.h | 6 ++++ > rcutree_plugin.h | 71 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ > sched.c | 69 ----------------------------------------------------- > 3 files changed, 77 insertions(+), 69 deletions(-) > diff --git a/kernel/rcutiny_plugin.h b/kernel/rcutiny_plugin.h > index 6ceca4f..87e226c 100644 > --- a/kernel/rcutiny_plugin.h > +++ b/kernel/rcutiny_plugin.h > @@ -461,6 +461,12 @@ void synchronize_rcu(void) > } > EXPORT_SYMBOL_GPL(synchronize_rcu); > > +void synchronize_sched_expedited(void) > +{ > + barrier(); > +} > +EXPORT_SYMBOL_GPL(synchronize_sched_expedited); > +
It would be better to put this in include/linux/rcutiny.h under #ifdef CONFIG_TINY_PREEMPT_RCU. The reason is that this would allow the EXPORT_SYMBOL_GPL() to be dropped, saving significant memory, at least from a TINY_RCU viewpoint. Could you please resubmit with this change?
(The reason we don't do the same for synchronize_sched() is that it needs cond_resched() in the CONFIG_TINY_RCU case.)
> static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq); > static unsigned long sync_rcu_preempt_exp_count; > static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex); > diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h > index 71a4147..9e62b01 100644 > --- a/kernel/rcutree_plugin.h > +++ b/kernel/rcutree_plugin.h > @@ -25,6 +25,7 @@ > */ > > #include <linux/delay.h> > +#include <linux/stop_machine.h> > > /* > * Check the RCU kernel configuration parameters and print informative > @@ -581,6 +582,76 @@ void synchronize_rcu(void) > } > EXPORT_SYMBOL_GPL(synchronize_rcu); > > +#ifndef CONFIG_SMP > + > +void synchronize_sched_expedited(void) > +{ > + barrier(); > +} > +EXPORT_SYMBOL_GPL(synchronize_sched_expedited); > + > +#else /* #ifndef CONFIG_SMP */ > + > +static atomic_t synchronize_sched_expedited_count = ATOMIC_INIT(0); > + > +static int synchronize_sched_expedited_cpu_stop(void *data) > +{ > + /* > + * There must be a full memory barrier on each affected CPU > + * between the time that try_stop_cpus() is called and the > + * time that it returns. > + * > + * In the current initial implementation of cpu_stop, the > + * above condition is already met when the control reaches > + * this point and the following smp_mb() is not strictly > + * necessary. Do smp_mb() anyway for documentation and > + * robustness against future implementation changes. > + */ > + smp_mb(); /* See above comment block. */ > + return 0; > +} > + > +/* > + * Wait for an rcu-sched grace period to elapse, but use "big hammer" > + * approach to force grace period to end quickly. This consumes > + * significant time on all CPUs, and is thus not recommended for > + * any sort of common-case code. > + * > + * Note that it is illegal to call this function while holding any > + * lock that is acquired by a CPU-hotplug notifier. Failing to > + * observe this restriction will result in deadlock. > + */ > +void synchronize_sched_expedited(void) > +{ > + int snap, trycount = 0; > + > + smp_mb(); /* ensure prior mod happens before capturing snap. */ > + snap = atomic_read(&synchronize_sched_expedited_count) + 1; > + get_online_cpus(); > + while (try_stop_cpus(cpu_online_mask, > + synchronize_sched_expedited_cpu_stop, > + NULL) == -EAGAIN) { > + put_online_cpus(); > + if (trycount++ < 10) > + udelay(trycount * num_online_cpus()); > + else { > + synchronize_sched(); > + return; > + } > + if (atomic_read(&synchronize_sched_expedited_count) - snap > 0) { > + smp_mb(); /* ensure test happens before caller kfree */ > + return; > + } > + get_online_cpus(); > + } > + atomic_inc(&synchronize_sched_expedited_count); > + smp_mb__after_atomic_inc(); /* ensure post-GP actions seen after GP. */ > + put_online_cpus(); > +} > +EXPORT_SYMBOL_GPL(synchronize_sched_expedited); > + > +#endif /* #else #ifndef CONFIG_SMP */ > + > static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq); > static long sync_rcu_preempt_exp_count; > static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex); > diff --git a/kernel/sched.c b/kernel/sched.c > index abf8440..9dc7775 100644 > --- a/kernel/sched.c > +++ b/kernel/sched.c > @@ -9332,72 +9332,3 @@ struct cgroup_subsys cpuacct_subsys = { > }; > #endif /* CONFIG_CGROUP_CPUACCT */ > > -#ifndef CONFIG_SMP > - > -void synchronize_sched_expedited(void) > -{ > - barrier(); > -} > -EXPORT_SYMBOL_GPL(synchronize_sched_expedited); > - > -#else /* #ifndef CONFIG_SMP */ > - > -static atomic_t synchronize_sched_expedited_count = ATOMIC_INIT(0); > - > -static int synchronize_sched_expedited_cpu_stop(void *data) > -{ > - /* > - * There must be a full memory barrier on each affected CPU > - * between the time that try_stop_cpus() is called and the > - * time that it returns. > - * > - * In the current initial implementation of cpu_stop, the > - * above condition is already met when the control reaches > - * this point and the following smp_mb() is not strictly > - * necessary. Do smp_mb() anyway for documentation and > - * robustness against future implementation changes. > - */ > - smp_mb(); /* See above comment block. */ > - return 0; > -} > - > -/* > - * Wait for an rcu-sched grace period to elapse, but use "big hammer" > - * approach to force grace period to end quickly. This consumes > - * significant time on all CPUs, and is thus not recommended for > - * any sort of common-case code. > - * > - * Note that it is illegal to call this function while holding any > - * lock that is acquired by a CPU-hotplug notifier. Failing to > - * observe this restriction will result in deadlock. > - */ > -void synchronize_sched_expedited(void) > -{ > - int snap, trycount = 0; > - > - smp_mb(); /* ensure prior mod happens before capturing snap. */ > - snap = atomic_read(&synchronize_sched_expedited_count) + 1; > - get_online_cpus(); > - while (try_stop_cpus(cpu_online_mask, > - synchronize_sched_expedited_cpu_stop, > - NULL) == -EAGAIN) { > - put_online_cpus(); > - if (trycount++ < 10) > - udelay(trycount * num_online_cpus()); > - else { > - synchronize_sched(); > - return; > - } > - if (atomic_read(&synchronize_sched_expedited_count) - snap > 0) { > - smp_mb(); /* ensure test happens before caller kfree */ > - return; > - } > - get_online_cpus(); > - } > - atomic_inc(&synchronize_sched_expedited_count); > - smp_mb__after_atomic_inc(); /* ensure post-GP actions seen after GP. */ > - put_online_cpus(); > -} > -EXPORT_SYMBOL_GPL(synchronize_sched_expedited); > - > -#endif /* #else #ifndef CONFIG_SMP */
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