dect
/
linux-2.6
Archived
13
0
Fork 0
Code Releases Activity

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>
This commit is contained in:
Xiao Guangrong 2009-09-22 16:43:39 -07:00 committed by Linus Torvalds
parent 5c72513843
commit 54fdade1c3
2 changed files with 20 additions and 21 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
include/linux/cpumask.h
View File

@ -714,6 +714,18 @@ static inline int cpumask_test_and_set_cpu(int cpu, struct cpumask *cpumask)
return test_and_set_bit(cpumask_check(cpu), cpumask_bits(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

29
kernel/smp.c
View File

@ -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.