Messages in this thread | | | Date | Sun, 26 Oct 2008 14:55:31 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH] rcupdate: reduce sys's overhead when rcu_barrier()s called simultaneous |
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On Fri, Oct 24, 2008 at 01:38:13PM +0800, Lai Jiangshan wrote: > > rcu_barrier() queues rcu_head on all cpus, it will brings > large overhead for a large system which has a lots cpu. > this fix reduces sys's overhead when rcu_barrier()s called > simultaneous.
Hello, Jiangshan,
If we were to have problems with many concurrent rcu_barrier() calls stacking up, this patch looks like it would be a reasonable was of addressing those problems.
But do we really have problems with this at the moment?
Thanx, Paul
> Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> > --- > diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c > index ad63af8..734850b 100644 > --- a/kernel/rcupdate.c > +++ b/kernel/rcupdate.c > @@ -53,6 +53,9 @@ enum rcu_barrier { > > static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL}; > static atomic_t rcu_barrier_cpu_count; > +static unsigned long rcu_barrier_completed; > +static unsigned long rcu_barrier_completed_bh; > +static unsigned long rcu_barrier_completed_sched; > static DEFINE_MUTEX(rcu_barrier_mutex); > static struct completion rcu_barrier_completion; > > @@ -60,7 +63,7 @@ static struct completion rcu_barrier_completion; > * Awaken the corresponding synchronize_rcu() instance now that a > * grace period has elapsed. > */ > -void wakeme_after_rcu(struct rcu_head *head) > +void wakeme_after_rcu(struct rcu_head *head) > { > struct rcu_synchronize *rcu; > > @@ -113,11 +116,20 @@ static void rcu_barrier_func(void *type) > * Orchestrate the specified type of RCU barrier, waiting for all > * RCU callbacks of the specified type to complete. > */ > -static void _rcu_barrier(enum rcu_barrier type) > +static void _rcu_barrier(enum rcu_barrier type, unsigned long *completed) > { > + unsigned long batch = ACCESS_ONCE(*completed); > BUG_ON(in_interrupt()); > /* Take cpucontrol mutex to protect against CPU hotplug */ > mutex_lock(&rcu_barrier_mutex); > + > + BUG_ON(*completed & 1); > + if ((*completed - batch) >= 2) { > + mutex_unlock(&rcu_barrier_mutex); > + return; > + } > + (*completed)++; > + > init_completion(&rcu_barrier_completion); > /* > * Initialize rcu_barrier_cpu_count to 1, then invoke > @@ -133,6 +145,7 @@ static void _rcu_barrier(enum rcu_barrier type) > if (atomic_dec_and_test(&rcu_barrier_cpu_count)) > complete(&rcu_barrier_completion); > wait_for_completion(&rcu_barrier_completion); > + (*completed)++; > mutex_unlock(&rcu_barrier_mutex); > } > > @@ -141,7 +154,7 @@ static void _rcu_barrier(enum rcu_barrier type) > */ > void rcu_barrier(void) > { > - _rcu_barrier(RCU_BARRIER_STD); > + _rcu_barrier(RCU_BARRIER_STD, &rcu_barrier_completed); > } > EXPORT_SYMBOL_GPL(rcu_barrier); > > @@ -150,7 +163,7 @@ EXPORT_SYMBOL_GPL(rcu_barrier); > */ > void rcu_barrier_bh(void) > { > - _rcu_barrier(RCU_BARRIER_BH); > + _rcu_barrier(RCU_BARRIER_BH, &rcu_barrier_completed_bh); > } > EXPORT_SYMBOL_GPL(rcu_barrier_bh); > > @@ -159,7 +172,7 @@ EXPORT_SYMBOL_GPL(rcu_barrier_bh); > */ > void rcu_barrier_sched(void) > { > - _rcu_barrier(RCU_BARRIER_SCHED); > + _rcu_barrier(RCU_BARRIER_SCHED, &rcu_barrier_completed_sched); > } > EXPORT_SYMBOL_GPL(rcu_barrier_sched); > > >
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