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cpumask: smp_call_function_many()
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Impact: Implementation change to remove cpumask_t from stack.

Actually change smp_call_function_mask() to smp_call_function_many().
We avoid cpumasks on the stack in this version.

(S390 has its own version, but that's going away apparently).

We have to do some dancing to figure out if 0 or 1 other cpus are in
the mask supplied and the online mask without allocating a tmp
cpumask.  It's still fairly cheap.

We allocate the cpumask at the end of the call_function_data
structure: if allocation fails we fallback to smp_call_function_single
rather than using the baroque quiescing code (which needs a cpumask on
stack).

(Thanks to Hiroshi Shimamoto for spotting several bugs in previous versions!)

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Mike Travis <travis@sgi.com>
Cc: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
Cc: npiggin@suse.de
Cc: axboe@kernel.dk
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Rusty Russell committed Dec 29, 2008
1 parent 3fa4152 commit 54b11e6
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Showing 2 changed files with 57 additions and 97 deletions.
15 changes: 8 additions & 7 deletions include/linux/smp.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -67,15 +67,16 @@ extern void smp_cpus_done(unsigned int max_cpus);
* Call a function on all other processors
*/
int smp_call_function(void(*func)(void *info), void *info, int wait);
/* Deprecated: use smp_call_function_many() which uses a cpumask ptr. */
int smp_call_function_mask(cpumask_t mask, void(*func)(void *info), void *info,
int wait);
void smp_call_function_many(const struct cpumask *mask,
void (*func)(void *info), void *info, bool wait);

static inline void smp_call_function_many(const struct cpumask *mask,
void (*func)(void *info), void *info,
int wait)
/* Deprecated: Use smp_call_function_many which takes a pointer to the mask. */
static inline int
smp_call_function_mask(cpumask_t mask, void(*func)(void *info), void *info,
int wait)
{
smp_call_function_mask(*mask, func, info, wait);
smp_call_function_many(&mask, func, info, wait);
return 0;
}

int smp_call_function_single(int cpuid, void (*func) (void *info), void *info,
Expand Down
139 changes: 49 additions & 90 deletions kernel/smp.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -24,8 +24,8 @@ struct call_function_data {
struct call_single_data csd;
spinlock_t lock;
unsigned int refs;
cpumask_t cpumask;
struct rcu_head rcu_head;
unsigned long cpumask_bits[];
};

struct call_single_queue {
Expand Down Expand Up @@ -110,13 +110,13 @@ void generic_smp_call_function_interrupt(void)
list_for_each_entry_rcu(data, &call_function_queue, csd.list) {
int refs;

if (!cpu_isset(cpu, data->cpumask))
if (!cpumask_test_cpu(cpu, to_cpumask(data->cpumask_bits)))
continue;

data->csd.func(data->csd.info);

spin_lock(&data->lock);
cpu_clear(cpu, data->cpumask);
cpumask_clear_cpu(cpu, to_cpumask(data->cpumask_bits));
WARN_ON(data->refs == 0);
data->refs--;
refs = data->refs;
Expand Down Expand Up @@ -266,51 +266,13 @@ void __smp_call_function_single(int cpu, struct call_single_data *data)
generic_exec_single(cpu, data);
}

/* Dummy function */
static void quiesce_dummy(void *unused)
{
}

/*
* Ensure stack based data used in call function mask is safe to free.
*
* This is needed by smp_call_function_mask when using on-stack data, because
* a single call function queue is shared by all CPUs, and any CPU may pick up
* the data item on the queue at any time before it is deleted. So we need to
* ensure that all CPUs have transitioned through a quiescent state after
* this call.
*
* This is a very slow function, implemented by sending synchronous IPIs to
* all possible CPUs. For this reason, we have to alloc data rather than use
* stack based data even in the case of synchronous calls. The stack based
* data is then just used for deadlock/oom fallback which will be very rare.
*
* If a faster scheme can be made, we could go back to preferring stack based
* data -- the data allocation/free is non-zero cost.
*/
static void smp_call_function_mask_quiesce_stack(cpumask_t mask)
{
struct call_single_data data;
int cpu;

data.func = quiesce_dummy;
data.info = NULL;

for_each_cpu_mask(cpu, mask) {
data.flags = CSD_FLAG_WAIT;
generic_exec_single(cpu, &data);
}
}

/**
* smp_call_function_mask(): Run a function on a set of other CPUs.
* @mask: The set of cpus to run on.
* smp_call_function_many(): Run a function on a set of other CPUs.
* @mask: The set of cpus to run on (only runs on online subset).
* @func: The function to run. This must be fast and non-blocking.
* @info: An arbitrary pointer to pass to the function.
* @wait: If true, wait (atomically) until function has completed on other CPUs.
*
* Returns 0 on success, else a negative status code.
*
* If @wait is true, then returns once @func has returned. Note that @wait
* will be implicitly turned on in case of allocation failures, since
* we fall back to on-stack allocation.
Expand All @@ -319,53 +281,57 @@ static void smp_call_function_mask_quiesce_stack(cpumask_t mask)
* hardware interrupt handler or from a bottom half handler. Preemption
* must be disabled when calling this function.
*/
int smp_call_function_mask(cpumask_t mask, void (*func)(void *), void *info,
int wait)
void smp_call_function_many(const struct cpumask *mask,
void (*func)(void *), void *info,
bool wait)
{
struct call_function_data d;
struct call_function_data *data = NULL;
cpumask_t allbutself;
struct call_function_data *data;
unsigned long flags;
int cpu, num_cpus;
int slowpath = 0;
int cpu, next_cpu;

/* Can deadlock when called with interrupts disabled */
WARN_ON(irqs_disabled());

cpu = smp_processor_id();
allbutself = cpu_online_map;
cpu_clear(cpu, allbutself);
cpus_and(mask, mask, allbutself);
num_cpus = cpus_weight(mask);

/*
* If zero CPUs, return. If just a single CPU, turn this request
* into a targetted single call instead since it's faster.
*/
if (!num_cpus)
return 0;
else if (num_cpus == 1) {
cpu = first_cpu(mask);
return smp_call_function_single(cpu, func, info, wait);
/* So, what's a CPU they want? Ignoring this one. */
cpu = cpumask_first_and(mask, cpu_online_mask);
if (cpu == smp_processor_id())
cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
/* No online cpus? We're done. */
if (cpu >= nr_cpu_ids)
return;

/* Do we have another CPU which isn't us? */
next_cpu = cpumask_next_and(cpu, mask, cpu_online_mask);
if (next_cpu == smp_processor_id())
next_cpu = cpumask_next_and(next_cpu, mask, cpu_online_mask);

/* Fastpath: do that cpu by itself. */
if (next_cpu >= nr_cpu_ids) {
smp_call_function_single(cpu, func, info, wait);
return;
}

data = kmalloc(sizeof(*data), GFP_ATOMIC);
if (data) {
data->csd.flags = CSD_FLAG_ALLOC;
if (wait)
data->csd.flags |= CSD_FLAG_WAIT;
} else {
data = &d;
data->csd.flags = CSD_FLAG_WAIT;
wait = 1;
slowpath = 1;
data = kmalloc(sizeof(*data) + cpumask_size(), GFP_ATOMIC);
if (unlikely(!data)) {
/* Slow path. */
for_each_online_cpu(cpu) {
if (cpu == smp_processor_id())
continue;
if (cpumask_test_cpu(cpu, mask))
smp_call_function_single(cpu, func, info, wait);
}
return;
}

spin_lock_init(&data->lock);
data->csd.flags = CSD_FLAG_ALLOC;
if (wait)
data->csd.flags |= CSD_FLAG_WAIT;
data->csd.func = func;
data->csd.info = info;
data->refs = num_cpus;
data->cpumask = mask;
cpumask_and(to_cpumask(data->cpumask_bits), mask, cpu_online_mask);
cpumask_clear_cpu(smp_processor_id(), to_cpumask(data->cpumask_bits));
data->refs = cpumask_weight(to_cpumask(data->cpumask_bits));

spin_lock_irqsave(&call_function_lock, flags);
list_add_tail_rcu(&data->csd.list, &call_function_queue);
Expand All @@ -377,26 +343,21 @@ int smp_call_function_mask(cpumask_t mask, void (*func)(void *), void *info,
smp_mb();

/* Send a message to all CPUs in the map */
arch_send_call_function_ipi(mask);
arch_send_call_function_ipi(*to_cpumask(data->cpumask_bits));

/* optionally wait for the CPUs to complete */
if (wait) {
if (wait)
csd_flag_wait(&data->csd);
if (unlikely(slowpath))
smp_call_function_mask_quiesce_stack(mask);
}

return 0;
}
EXPORT_SYMBOL(smp_call_function_mask);
EXPORT_SYMBOL(smp_call_function_many);

/**
* smp_call_function(): Run a function on all other CPUs.
* @func: The function to run. This must be fast and non-blocking.
* @info: An arbitrary pointer to pass to the function.
* @wait: If true, wait (atomically) until function has completed on other CPUs.
*
* Returns 0 on success, else a negative status code.
* Returns 0.
*
* If @wait is true, then returns once @func has returned; otherwise
* it returns just before the target cpu calls @func. In case of allocation
Expand All @@ -407,12 +368,10 @@ EXPORT_SYMBOL(smp_call_function_mask);
*/
int smp_call_function(void (*func)(void *), void *info, int wait)
{
int ret;

preempt_disable();
ret = smp_call_function_mask(cpu_online_map, func, info, wait);
smp_call_function_many(cpu_online_mask, func, info, wait);
preempt_enable();
return ret;
return 0;
}
EXPORT_SYMBOL(smp_call_function);

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