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: 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
diff --git a/kernel/smp.c b/kernel/smp.c
index 75c8dde..9f0eafe 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -24,8 +24,8 @@
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 @@
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 @@
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 @@
* 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;
- /*
- * 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);
+ /* 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);
@@ -377,18 +343,13 @@
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 @@
* @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 @@
*/
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);