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Date: Mon, 27 Oct 2008 13:49:49 +0800 From: Lai Jiangshan <laijs@...fujitsu.com> To: paulmck@...ux.vnet.ibm.com CC: Ingo Molnar <mingo@...e.hu>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] rcupdate: reduce sys's overhead when rcu_barrier()s called simultaneous Paul E. McKenney wrote: > 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 Hi, Paul, Thanks, we do not have problems with this at the moment. I suddenly had an association of ideas to synchronize_srcu(), so I made use of the ideas in synchronize_srcu() and this patch was made. Thanx, Lai. > >> Signed-off-by: Lai Jiangshan <laijs@...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); >> >> >> > > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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