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Date: Wed, 18 Dec 2013 21:51:13 +0100
From: Jan Kara <jack@...e.cz>
To: Jens Axboe <jaxboe@...ionio.com>
Cc: Christoph Hellwig <hch@...radead.org>,
LKML <linux-kernel@...r.kernel.org>,
Christoph Hellwig <hch@....de>, Jan Kara <jack@...e.cz>
Subject: Re: [PATCH 3/3] kernel: use lockless list for
smp_call_function_single()
On Wed 18-12-13 18:23:38, Jan Kara wrote:
> From: Christoph Hellwig <hch@....de>
>
> Make smp_call_function_single and friends more efficient by using
> a lockless list.
This is the correct patch 3/3.
Honza
>
> Signed-off-by: Christoph Hellwig <hch@....de>
> Signed-off-by: Jan Kara <jack@...e.cz>
> ---
> include/linux/elevator.h | 2 +-
> include/linux/smp.h | 3 ++-
> kernel/smp.c | 51 ++++++++++--------------------------------------
> 3 files changed, 13 insertions(+), 43 deletions(-)
>
> diff --git a/include/linux/elevator.h b/include/linux/elevator.h
> index 0bdfd46f4735..06860e2a25c3 100644
> --- a/include/linux/elevator.h
> +++ b/include/linux/elevator.h
> @@ -205,7 +205,7 @@ enum {
> #define rq_entry_fifo(ptr) list_entry((ptr), struct request, queuelist)
> #define rq_fifo_clear(rq) do { \
> list_del_init(&(rq)->queuelist); \
> - INIT_LIST_HEAD(&(rq)->csd.list); \
> + (rq)->csd.llist.next = NULL; \
> } while (0)
>
> #else /* CONFIG_BLOCK */
> diff --git a/include/linux/smp.h b/include/linux/smp.h
> index 5da22ee42e16..9a1b8ba05924 100644
> --- a/include/linux/smp.h
> +++ b/include/linux/smp.h
> @@ -11,12 +11,13 @@
> #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;
> + struct llist_node llist;
> smp_call_func_t func;
> void *info;
> u16 flags;
> diff --git a/kernel/smp.c b/kernel/smp.c
> index bd9f94028838..47b415e16c24 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)
> @@ -177,26 +159,19 @@ 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;
> + struct call_single_data *csd, *csd_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);
> -
> - while (!list_empty(&list)) {
> - struct call_single_data *csd;
> -
> - csd = list_entry(list.next, struct call_single_data, list);
> - list_del(&csd->list);
> + entry = llist_del_all(&__get_cpu_var(call_single_queue));
> + entry = llist_reverse_order(entry);
>
> + llist_for_each_entry_safe(csd, csd_next, entry, llist) {
> csd->func(csd->info);
> -
> csd_unlock(csd);
> }
> }
> @@ -411,17 +386,11 @@ 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 */
> --
> 1.8.1.4
>
--
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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