Messages in this thread Patch in this message | | | Date | Fri, 24 Oct 2008 13:38:13 +0800 | From | Lai Jiangshan <> | Subject | [PATCH] rcupdate: reduce sys's overhead when rcu_barrier()s called simultaneous |
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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.
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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