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Subject[PATCH 1/1] cpumask: smp_call_function_many()

Actually change smp_call_function_mask() to smp_call_function_many().

S390 has its own version, so we do trivial conversion on that too.

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.

(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: schwidefsky@de.ibm.com
Cc: heiko.carstens@de.ibm.com
Cc: npiggin@suse.de
Cc: axboe@kernel.dk
---
arch/s390/include/asm/smp.h | 3
arch/s390/kernel/smp.c | 9 +-
include/linux/smp.h | 15 ++--
kernel/smp.c | 137 +++++++++++++++-----------------------------
4 files changed, 60 insertions(+), 104 deletions(-)

diff -r a701ec4491ec arch/s390/include/asm/smp.h
--- a/arch/s390/include/asm/smp.h Tue Nov 18 12:08:41 2008 +1030
+++ b/arch/s390/include/asm/smp.h Tue Nov 18 12:10:56 2008 +1030
@@ -90,9 +90,6 @@

extern struct mutex smp_cpu_state_mutex;
extern int smp_cpu_polarization[];
-
-extern int smp_call_function_mask(cpumask_t mask, void (*func)(void *),
- void *info, int wait);
#endif

#ifndef CONFIG_SMP
diff -r a701ec4491ec arch/s390/kernel/smp.c
--- a/arch/s390/kernel/smp.c Tue Nov 18 12:08:41 2008 +1030
+++ b/arch/s390/kernel/smp.c Tue Nov 18 12:10:56 2008 +1030
@@ -199,7 +199,7 @@
EXPORT_SYMBOL(smp_call_function_single);

/**
- * smp_call_function_mask(): Run a function on a set of other CPUs.
+ * smp_call_function_many(): Run a function on a set of other CPUs.
* @mask: The set of cpus to run on. Must not include the current cpu.
* @func: The function to run. This must be fast and non-blocking.
* @info: An arbitrary pointer to pass to the function.
@@ -213,16 +213,17 @@
* You must not call this function with disabled interrupts or from a
* hardware interrupt handler or from a bottom half handler.
*/
-int smp_call_function_mask(cpumask_t mask, void (*func)(void *), void *info,
- int wait)
+int smp_call_function_many(const struct cpumask *maskp,
+ void (*func)(void *), void *info, bool wait)
{
+ cpumask_t mask = *maskp;
spin_lock(&call_lock);
cpu_clear(smp_processor_id(), mask);
__smp_call_function_map(func, info, wait, mask);
spin_unlock(&call_lock);
return 0;
}
-EXPORT_SYMBOL(smp_call_function_mask);
+EXPORT_SYMBOL(smp_call_function_many);

void smp_send_stop(void)
{
diff -r a701ec4491ec include/linux/smp.h
--- a/include/linux/smp.h Tue Nov 18 12:08:41 2008 +1030
+++ b/include/linux/smp.h Tue Nov 18 12:10:56 2008 +1030
@@ -64,15 +64,16 @@
* 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,
diff -r a701ec4491ec kernel/smp.c
--- a/kernel/smp.c Tue Nov 18 12:08:41 2008 +1030
+++ b/kernel/smp.c Tue Nov 18 12:10:56 2008 +1030
@@ -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;
@@ -266,50 +266,12 @@
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
@@ -319,53 +281,55 @@
* 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);

- 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;
+ /* Fastpath: do that cpu by itself. */
+ if (next_cpu >= nr_cpu_ids)
+ 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;
}

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 +341,13 @@
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 +355,7 @@
* @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 +366,10 @@
*/
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);



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