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authorXiao Guangrong <xiaoguangrong@cn.fujitsu.com>2009-09-22 16:43:39 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2009-09-23 07:39:28 -0700
commit54fdade1c3332391948ec43530c02c4794a38172 (patch)
treea44cfa6888bbe702321e4d4737786e5292d72eaa
parent5c725138437837291db5c25f4a076ee852e806e3 (diff)
generic-ipi: make struct call_function_data lockless
This patch can remove spinlock from struct call_function_data, the reasons are below: 1: add a new interface for cpumask named cpumask_test_and_clear_cpu(), it can atomically test and clear specific cpu, we can use it instead of cpumask_test_cpu() and cpumask_clear_cpu() and no need data->lock to protect those in generic_smp_call_function_interrupt(). 2: in smp_call_function_many(), after csd_lock() return, the current's cfd_data is deleted from call_function list, so it not have race between other cpus, then cfs_data is only used in smp_call_function_many() that must disable preemption and not from a hardware interrupthandler or from a bottom half handler to call, only the correspond cpu can use it, so it not have race in current cpu, no need cfs_data->lock to protect it. 3: after 1 and 2, cfs_data->lock is only use to protect cfs_data->refs in generic_smp_call_function_interrupt(), so we can define cfs_data->refs to atomic_t, and no need cfs_data->lock any more. Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Jens Axboe <jens.axboe@oracle.com> Cc: Nick Piggin <nickpiggin@yahoo.com.au> Cc: Peter Zijlstra <peterz@infradead.org> Acked-by: Rusty Russell <rusty@rustcorp.com.au> [akpm@linux-foundation.org: use atomic_dec_return()] Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--include/linux/cpumask.h12
-rw-r--r--kernel/smp.c29
2 files changed, 20 insertions, 21 deletions
diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index 796df12091b7..9b1d458aac6e 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -715,6 +715,18 @@ static inline int cpumask_test_and_set_cpu(int cpu, struct cpumask *cpumask)
}
/**
+ * cpumask_test_and_clear_cpu - atomically test and clear a cpu in a cpumask
+ * @cpu: cpu number (< nr_cpu_ids)
+ * @cpumask: the cpumask pointer
+ *
+ * test_and_clear_bit wrapper for cpumasks.
+ */
+static inline int cpumask_test_and_clear_cpu(int cpu, struct cpumask *cpumask)
+{
+ return test_and_clear_bit(cpumask_check(cpu), cpumask_bits(cpumask));
+}
+
+/**
* cpumask_setall - set all cpus (< nr_cpu_ids) in a cpumask
* @dstp: the cpumask pointer
*/
diff --git a/kernel/smp.c b/kernel/smp.c
index 8e218500ab14..fd47a256a24e 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -29,8 +29,7 @@ enum {
struct call_function_data {
struct call_single_data csd;
- spinlock_t lock;
- unsigned int refs;
+ atomic_t refs;
cpumask_var_t cpumask;
};
@@ -39,9 +38,7 @@ struct call_single_queue {
spinlock_t lock;
};
-static DEFINE_PER_CPU(struct call_function_data, cfd_data) = {
- .lock = __SPIN_LOCK_UNLOCKED(cfd_data.lock),
-};
+static DEFINE_PER_CPU(struct call_function_data, cfd_data);
static int
hotplug_cfd(struct notifier_block *nfb, unsigned long action, void *hcpu)
@@ -196,25 +193,18 @@ void generic_smp_call_function_interrupt(void)
list_for_each_entry_rcu(data, &call_function.queue, csd.list) {
int refs;
- spin_lock(&data->lock);
- if (!cpumask_test_cpu(cpu, data->cpumask)) {
- spin_unlock(&data->lock);
+ if (!cpumask_test_and_clear_cpu(cpu, data->cpumask))
continue;
- }
- cpumask_clear_cpu(cpu, data->cpumask);
- spin_unlock(&data->lock);
data->csd.func(data->csd.info);
- spin_lock(&data->lock);
- WARN_ON(data->refs == 0);
- refs = --data->refs;
+ refs = atomic_dec_return(&data->refs);
+ WARN_ON(refs < 0);
if (!refs) {
spin_lock(&call_function.lock);
list_del_rcu(&data->csd.list);
spin_unlock(&call_function.lock);
}
- spin_unlock(&data->lock);
if (refs)
continue;
@@ -419,23 +409,20 @@ void smp_call_function_many(const struct cpumask *mask,
data = &__get_cpu_var(cfd_data);
csd_lock(&data->csd);
- spin_lock_irqsave(&data->lock, flags);
data->csd.func = func;
data->csd.info = info;
cpumask_and(data->cpumask, mask, cpu_online_mask);
cpumask_clear_cpu(this_cpu, data->cpumask);
- data->refs = cpumask_weight(data->cpumask);
+ atomic_set(&data->refs, cpumask_weight(data->cpumask));
- spin_lock(&call_function.lock);
+ spin_lock_irqsave(&call_function.lock, flags);
/*
* Place entry at the _HEAD_ of the list, so that any cpu still
* observing the entry in generic_smp_call_function_interrupt()
* will not miss any other list entries:
*/
list_add_rcu(&data->csd.list, &call_function.queue);
- spin_unlock(&call_function.lock);
-
- spin_unlock_irqrestore(&data->lock, flags);
+ spin_unlock_irqrestore(&call_function.lock, flags);
/*
* Make the list addition visible before sending the ipi.