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Date: Wed, 20 Oct 2010 21:39:53 -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 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.
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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