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Message-ID: <20101021161627.GA8004@linux.vnet.ibm.com>
Date: Thu, 21 Oct 2010 09:16:27 -0700
From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To: Lai Jiangshan <laijs@...fujitsu.com>
Cc: Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2 v2] rcu,cleanup: move synchronize_sched_expedited()
out of sched.c
On Wed, Oct 20, 2010 at 09:39:53PM -0700, Paul E. McKenney wrote:
> On Thu, Oct 21, 2010 at 11:29:05AM +0800, Lai Jiangshan wrote:
> > On 10/21/2010 08:19 AM, Paul E. McKenney wrote:
> > > On Wed, Oct 20, 2010 at 12:15:12PM -0700, Paul E. McKenney wrote:
> > >> On Wed, Oct 20, 2010 at 02:12:58PM +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/rcutree_plugin.h
> > >>> or include/linux/rcutiny.h instead of kerenl/rcupdate.c
> > >>
> > >> Queued, thank you!!!
> > >
> > > Hello again, Lai,
> > >
> > > I hit the following build error during testing:
> > >
> > > kernel/built-in.o: In function `.synchronize_rcu_expedited':
> > > (.text+0x787d8): undefined reference to `.synchronize_sched_expedited'
> > > kernel/built-in.o:(.toc1+0x1fe0): undefined reference to `synchronize_sched_expedited'
> > >
> > > This build uses defconfig with the following applied:
> > >
> > > CONFIG_RCU_TRACE=y
> > > CONFIG_RCU_FAST_NO_HZ=y
> > > CONFIG_NO_HZ=y
> > > CONFIG_RCU_CPU_STALL_DETECTOR=y
> > > CONFIG_SMP=y
> > > CONFIG_RCU_FANOUT=8
> > > CONFIG_NR_CPUS=8
> > > CONFIG_RCU_FANOUT_EXACT=n
> > > CONFIG_HOTPLUG_CPU=y
> > > CONFIG_PREEMPT_NONE=y
> > > CONFIG_PREEMPT_VOLUNTARY=n
> > > CONFIG_PREEMPT=n
> > > CONFIG_TREE_RCU=y
> > > CONFIG_TREE_PREEMPT_RCU=n
> > > CONFIG_RCU_TORTURE_TEST=m
> > > CONFIG_MODULE_UNLOAD=y
> > > CONFIG_SYSFS_DEPRECATED_V2=y
> > > CONFIG_IKCONFIG=y
> > > CONFIG_IKCONFIG_PROC=y
> > >
> > > Thoughts?
> > >
> > > Thanx, Paul
> > >
> > >
> >
> > I moved the code into CONFIG_TREE_PREEMPT_RCU=y codes. fixed version:
>
> Thank you, queued and am retesting.
And the new version works much better, thank you! Any news on the
cpumask_any() issue?
Thanx, Paul
> > Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
> > ---
> > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> > index 0d0b640..ead36da 100644
> > --- a/include/linux/rcupdate.h
> > +++ b/include/linux/rcupdate.h
> > @@ -66,7 +66,6 @@ extern void call_rcu_sched(struct rcu_head *head,
> > extern void synchronize_sched(void);
> > extern void rcu_barrier_bh(void);
> > extern void rcu_barrier_sched(void);
> > -extern void synchronize_sched_expedited(void);
> > extern int sched_expedited_torture_stats(char *page);
> >
> > static inline void __rcu_read_lock_bh(void)
> > diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
> > index 13877cb..4d84452 100644
> > --- a/include/linux/rcutiny.h
> > +++ b/include/linux/rcutiny.h
> > @@ -58,6 +58,11 @@ static inline void synchronize_rcu_bh_expedited(void)
> > synchronize_sched();
> > }
> >
> > +static inline void synchronize_sched_expedited(void)
> > +{
> > + synchronize_sched();
> > +}
> > +
> > #ifdef CONFIG_TINY_RCU
> >
> > static inline void rcu_preempt_note_context_switch(void)
> > diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
> > index 95518e6..9a1fd6c 100644
> > --- a/include/linux/rcutree.h
> > +++ b/include/linux/rcutree.h
> > @@ -47,6 +47,7 @@ static inline void exit_rcu(void)
> > #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
> >
> > extern void synchronize_rcu_bh(void);
> > +extern void synchronize_sched_expedited(void);
> > extern void synchronize_rcu_expedited(void);
> >
> > static inline void synchronize_rcu_bh_expedited(void)
> > diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
> > index 0e75d60..0de359b 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
> > @@ -1014,6 +1015,76 @@ static void __init __rcu_init_preempt(void)
> >
> > #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
> >
> > +#ifndef CONFIG_SMP
> > +
> > +void synchronize_sched_expedited(void)
> > +{
> > + cond_resched();
> > +}
> > +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 */
> > +
> > #if !defined(CONFIG_RCU_FAST_NO_HZ)
> >
> > /*
> > 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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