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SubjectRe: [PATCH 6/7] kernel: use lockless list for smp_call_function_single
On Thu 24-10-13 08:19:27, Christoph Hellwig wrote:
> Make smp_call_function_single and friends more efficient by using
> a lockless list.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> include/linux/blkdev.h | 5 +----
> include/linux/smp.h | 6 +++++-
> kernel/smp.c | 51 ++++++++++++------------------------------------
> 3 files changed, 19 insertions(+), 43 deletions(-)
>
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index f26ec20f..287bf7c 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -95,10 +95,7 @@ enum rq_cmd_type_bits {
> * as well!
> */
> struct request {
> - union {
> - struct list_head queuelist;
> - struct llist_node ll_list;
> - };
> + struct list_head queuelist;
> union {
> struct call_single_data csd;
> struct work_struct mq_flush_data;
> diff --git a/include/linux/smp.h b/include/linux/smp.h
> index 7885151..10755dd 100644
> --- a/include/linux/smp.h
> +++ b/include/linux/smp.h
> @@ -11,12 +11,16 @@
> #include <linux/list.h>
> #include <linux/cpumask.h>
> #include <linux/init.h>
> +#include <linux/llist.h>
>
> extern void cpu_idle(void);
>
> typedef void (*smp_call_func_t)(void *info);
> struct call_single_data {
> - struct list_head list;
> + union {
> + struct list_head list;
> + struct llist_node llist;
> + };
I'm wondering: Who's still using the normal list_head? I was grepping for
a while and I couldn't find any user. Otherwise the patch looks good to me.
You can add:
Reviewed-by: Jan Kara <jack@suse.cz>

Honza

> smp_call_func_t func;
> void *info;
> u16 flags;
> diff --git a/kernel/smp.c b/kernel/smp.c
> index 53644e6..a735c66 100644
> --- a/kernel/smp.c
> +++ b/kernel/smp.c
> @@ -28,12 +28,7 @@ struct call_function_data {
>
> static DEFINE_PER_CPU_SHARED_ALIGNED(struct call_function_data, cfd_data);
>
> -struct call_single_queue {
> - struct list_head list;
> - raw_spinlock_t lock;
> -};
> -
> -static DEFINE_PER_CPU_SHARED_ALIGNED(struct call_single_queue, call_single_queue);
> +static DEFINE_PER_CPU_SHARED_ALIGNED(struct llist_head, call_single_queue);
>
> static int
> hotplug_cfd(struct notifier_block *nfb, unsigned long action, void *hcpu)
> @@ -85,12 +80,8 @@ void __init call_function_init(void)
> void *cpu = (void *)(long)smp_processor_id();
> int i;
>
> - for_each_possible_cpu(i) {
> - struct call_single_queue *q = &per_cpu(call_single_queue, i);
> -
> - raw_spin_lock_init(&q->lock);
> - INIT_LIST_HEAD(&q->list);
> - }
> + for_each_possible_cpu(i)
> + init_llist_head(&per_cpu(call_single_queue, i));
>
> hotplug_cfd(&hotplug_cfd_notifier, CPU_UP_PREPARE, cpu);
> register_cpu_notifier(&hotplug_cfd_notifier);
> @@ -141,18 +132,9 @@ static void csd_unlock(struct call_single_data *csd)
> */
> static void generic_exec_single(int cpu, struct call_single_data *csd, int wait)
> {
> - struct call_single_queue *dst = &per_cpu(call_single_queue, cpu);
> - unsigned long flags;
> - int ipi;
> -
> if (wait)
> csd->flags |= CSD_FLAG_WAIT;
>
> - raw_spin_lock_irqsave(&dst->lock, flags);
> - ipi = list_empty(&dst->list);
> - list_add_tail(&csd->list, &dst->list);
> - raw_spin_unlock_irqrestore(&dst->lock, flags);
> -
> /*
> * The list addition should be visible before sending the IPI
> * handler locks the list to pull the entry off it because of
> @@ -164,7 +146,7 @@ static void generic_exec_single(int cpu, struct call_single_data *csd, int wait)
> * locking and barrier primitives. Generic code isn't really
> * equipped to do the right thing...
> */
> - if (ipi)
> + if (llist_add(&csd->llist, &per_cpu(call_single_queue, cpu)))
> arch_send_call_function_single_ipi(cpu);
>
> if (wait)
> @@ -177,27 +159,26 @@ static void generic_exec_single(int cpu, struct call_single_data *csd, int wait)
> */
> void generic_smp_call_function_single_interrupt(void)
> {
> - struct call_single_queue *q = &__get_cpu_var(call_single_queue);
> - LIST_HEAD(list);
> + struct llist_node *entry, *next;
>
> /*
> * Shouldn't receive this interrupt on a cpu that is not yet online.
> */
> WARN_ON_ONCE(!cpu_online(smp_processor_id()));
>
> - raw_spin_lock(&q->lock);
> - list_replace_init(&q->list, &list);
> - raw_spin_unlock(&q->lock);
> + entry = llist_del_all(&__get_cpu_var(call_single_queue));
> + entry = llist_reverse_order(entry);
>
> - while (!list_empty(&list)) {
> + while (entry) {
> struct call_single_data *csd;
>
> - csd = list_entry(list.next, struct call_single_data, list);
> - list_del(&csd->list);
> + next = entry->next;
>
> + csd = llist_entry(entry, struct call_single_data, llist);
> csd->func(csd->info);
> -
> csd_unlock(csd);
> +
> + entry = next;
> }
> }
>
> @@ -410,17 +391,11 @@ void smp_call_function_many(const struct cpumask *mask,
>
> for_each_cpu(cpu, cfd->cpumask) {
> struct call_single_data *csd = per_cpu_ptr(cfd->csd, cpu);
> - struct call_single_queue *dst =
> - &per_cpu(call_single_queue, cpu);
> - unsigned long flags;
>
> csd_lock(csd);
> csd->func = func;
> csd->info = info;
> -
> - raw_spin_lock_irqsave(&dst->lock, flags);
> - list_add_tail(&csd->list, &dst->list);
> - raw_spin_unlock_irqrestore(&dst->lock, flags);
> + llist_add(&csd->llist, &per_cpu(call_single_queue, cpu));
> }
>
> /* Send a message to all CPUs in the map */
> --
> 1.7.10.4
>
>
> --
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--
Jan Kara <jack@suse.cz>
SUSE Labs, CR


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