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Commit 54b11e6d authored by Rusty Russell's avatar Rusty Russell
Browse files

cpumask: smp_call_function_many() 



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: default avatarRusty Russell <rusty@rustcorp.com.au>
Signed-off-by: default avatarMike Travis <travis@sgi.com>
Cc: Hiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
Cc: npiggin@suse.de
Cc: axboe@kernel.dk
parent 3fa41520

include/linux/smp.h

+8 −7
Original line number Diff line number Diff line
@@ -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,

/* 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,

kernel/smp.c

+49 −90
Original line number Diff line number Diff line
@@ -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 {
@@ -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;
@@ -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.
@@ -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);

	/* 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;

	}



	/*

	 * 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);

	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;

	}



	data = kmalloc(sizeof(*data), GFP_ATOMIC);

	if (data) {

	spin_lock_init(&data->lock);

	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;

	}



	spin_lock_init(&data->lock);

	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);
@@ -377,18 +343,13 @@ 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.
@@ -396,7 +357,7 @@ EXPORT_SYMBOL(smp_call_function_mask); 
 * @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
@@ -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);