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SubjectRe: [PATCH 1/1] cpumask: smp_call_function_many()
Rusty Russell wrote:
> 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);

Hi Rusty,

I think, return is needed here. If not func will be called twice.

if (next_cpu >= nr_cpu_ids) {
smp_call_function_single(cpu, func, info, wait);
return;
}

thanks,
Hiroshi Shimamoto

> +
> + 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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