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Message-ID: <u2w7b6bb4a51004280047s8748cbfbi7ed8e2a238121fa9@mail.gmail.com>
Date: Wed, 28 Apr 2010 15:47:54 +0800
From: Xiaotian Feng <xtfeng@...il.com>
To: Changli Gao <xiaosuo@...il.com>
Cc: Ingo Molnar <mingo@...e.hu>,
Alexander Viro <viro@...iv.linux.org.uk>,
Andrew Morton <akpm@...ux-foundation.org>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
Davide Libenzi <davidel@...ilserver.org>,
Roland Dreier <rolandd@...co.com>,
Stefan Richter <stefanr@...6.in-berlin.de>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
"David S. Miller" <davem@...emloft.net>,
Eric Dumazet <dada1@...mosbay.com>,
Christoph Lameter <cl@...ux.com>,
Andreas Herrmann <andreas.herrmann3@....com>,
Thomas Gleixner <tglx@...utronix.de>,
David Howells <dhowells@...hat.com>,
Takashi Iwai <tiwai@...e.de>, linux-fsdevel@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [RFC] sched: implement the exclusive wait queue as a LIFO queue
On Wed, Apr 28, 2010 at 1:03 PM, Changli Gao <xiaosuo@...il.com> wrote:
> implement the exclusive wait queue as a LIFO queue
>
> If the exclusive wait queue is also a LIFO queue as the normal wait queue, the
> process who goes to sleep recently, will be woke up first. As its memory is
> more likely in cache, we will get better performance. And when there are many
> processes waiting on a exclusive wait queue, some of them may not be woke up,
> if the others can handle the workload, and it will reduce the load of
> the scheduler.
>
Starve some processes for performance?
> Note: before applying this patch, you need my previous patch patched first.
> https://patchwork.kernel.org/patch/95600/
>
> Signed-off-by: Changli Gao <xiaosuo@...il.com>
> ----
> fs/eventpoll.c | 3 +--
> include/linux/wait.h | 17 +++++++----------
> kernel/sched.c | 8 ++++----
> kernel/wait.c | 9 +++------
> 4 files changed, 15 insertions(+), 22 deletions(-)
> diff --git a/fs/eventpoll.c b/fs/eventpoll.c
> index bd056a5..e9b3ebe 100644
> --- a/fs/eventpoll.c
> +++ b/fs/eventpoll.c
> @@ -1140,8 +1140,7 @@ retry:
> * ep_poll_callback() when events will become available.
> */
> init_waitqueue_entry(&wait, current);
> - wait.flags |= WQ_FLAG_EXCLUSIVE;
> - __add_wait_queue(&ep->wq, &wait);
> + __add_wait_queue_ex(&ep->wq, &wait);
>
> for (;;) {
> /*
> diff --git a/include/linux/wait.h b/include/linux/wait.h
> index a48e16b..95c127d 100644
> --- a/include/linux/wait.h
> +++ b/include/linux/wait.h
> @@ -30,8 +30,6 @@ typedef int (*wait_queue_func_t)(wait_queue_t *wait, unsigned mode, int flags, v
> int default_wake_function(wait_queue_t *wait, unsigned mode, int flags, void *key);
>
> struct __wait_queue {
> - unsigned int flags;
> -#define WQ_FLAG_EXCLUSIVE 0x01
> void *private;
> wait_queue_func_t func;
> struct list_head task_list;
> @@ -50,6 +48,7 @@ struct wait_bit_queue {
> struct __wait_queue_head {
> spinlock_t lock;
> struct list_head task_list;
> + struct list_head task_list_ex;
> };
> typedef struct __wait_queue_head wait_queue_head_t;
>
> @@ -69,7 +68,8 @@ struct task_struct;
>
> #define __WAIT_QUEUE_HEAD_INITIALIZER(name) { \
> .lock = __SPIN_LOCK_UNLOCKED(name.lock), \
> - .task_list = { &(name).task_list, &(name).task_list } }
> + .task_list = { &(name).task_list, &(name).task_list }, \
> + .task_list_ex = { &(name).task_list_ex, &(name).task_list_ex } }
>
> #define DECLARE_WAIT_QUEUE_HEAD(name) \
> wait_queue_head_t name = __WAIT_QUEUE_HEAD_INITIALIZER(name)
> @@ -97,7 +97,6 @@ extern void __init_waitqueue_head(wait_queue_head_t *q, struct lock_class_key *)
>
> static inline void init_waitqueue_entry(wait_queue_t *q, struct task_struct *p)
> {
> - q->flags = 0;
> q->private = p;
> q->func = default_wake_function;
> }
> @@ -105,14 +104,13 @@ static inline void init_waitqueue_entry(wait_queue_t *q, struct task_struct *p)
> static inline void init_waitqueue_func_entry(wait_queue_t *q,
> wait_queue_func_t func)
> {
> - q->flags = 0;
> q->private = NULL;
> q->func = func;
> }
>
> static inline int waitqueue_active(wait_queue_head_t *q)
> {
> - return !list_empty(&q->task_list);
> + return !list_empty(&q->task_list) || !list_empty(&q->task_list);
> }
>
> extern void add_wait_queue(wait_queue_head_t *q, wait_queue_t *wait);
> @@ -127,10 +125,10 @@ static inline void __add_wait_queue(wait_queue_head_t *head, wait_queue_t *new)
> /*
> * Used for wake-one threads:
> */
> -static inline void __add_wait_queue_tail(wait_queue_head_t *head,
> +static inline void __add_wait_queue_ex(wait_queue_head_t *head,
> wait_queue_t *new)
> {
> - list_add_tail(&new->task_list, &head->task_list);
> + list_add(&new->task_list, &head->task_list_ex);
> }
>
> static inline void __remove_wait_queue(wait_queue_head_t *head,
> @@ -409,8 +407,7 @@ do { \
> static inline void add_wait_queue_exclusive_locked(wait_queue_head_t *q,
> wait_queue_t * wait)
> {
> - wait->flags |= WQ_FLAG_EXCLUSIVE;
> - __add_wait_queue_tail(q, wait);
> + __add_wait_queue_ex(q, wait);
> }
>
> /*
> diff --git a/kernel/sched.c b/kernel/sched.c
> index be5ab70..59b1534 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -3903,11 +3903,11 @@ static void __wake_up_common(wait_queue_head_t *q, unsigned int mode,
> {
> wait_queue_t *curr, *next;
>
> - list_for_each_entry_safe(curr, next, &q->task_list, task_list) {
> - unsigned flags = curr->flags;
> + list_for_each_entry_safe(curr, next, &q->task_list, task_list)
> + curr->func(curr, mode, wake_flags, key);
>
> - if (curr->func(curr, mode, wake_flags, key) &&
> - (flags & WQ_FLAG_EXCLUSIVE) && !--nr_exclusive)
> + list_for_each_entry_safe(curr, next, &q->task_list_ex, task_list) {
> + if (curr->func(curr, mode, wake_flags, key) && !--nr_exclusive)
> break;
> }
> }
> diff --git a/kernel/wait.c b/kernel/wait.c
> index c4bd3d8..a0559df 100644
> --- a/kernel/wait.c
> +++ b/kernel/wait.c
> @@ -15,6 +15,7 @@ void __init_waitqueue_head(wait_queue_head_t *q, struct lock_class_key *key)
> spin_lock_init(&q->lock);
> lockdep_set_class(&q->lock, key);
> INIT_LIST_HEAD(&q->task_list);
> + INIT_LIST_HEAD(&q->task_list_ex);
> }
>
> EXPORT_SYMBOL(__init_waitqueue_head);
> @@ -23,7 +24,6 @@ void add_wait_queue(wait_queue_head_t *q, wait_queue_t *wait)
> {
> unsigned long flags;
>
> - wait->flags &= ~WQ_FLAG_EXCLUSIVE;
> spin_lock_irqsave(&q->lock, flags);
> __add_wait_queue(q, wait);
> spin_unlock_irqrestore(&q->lock, flags);
> @@ -34,9 +34,8 @@ void add_wait_queue_exclusive(wait_queue_head_t *q, wait_queue_t *wait)
> {
> unsigned long flags;
>
> - wait->flags |= WQ_FLAG_EXCLUSIVE;
> spin_lock_irqsave(&q->lock, flags);
> - __add_wait_queue_tail(q, wait);
> + __add_wait_queue_ex(q, wait);
> spin_unlock_irqrestore(&q->lock, flags);
> }
> EXPORT_SYMBOL(add_wait_queue_exclusive);
> @@ -69,7 +68,6 @@ prepare_to_wait(wait_queue_head_t *q, wait_queue_t *wait, int state)
> {
> unsigned long flags;
>
> - wait->flags &= ~WQ_FLAG_EXCLUSIVE;
> spin_lock_irqsave(&q->lock, flags);
> if (list_empty(&wait->task_list))
> __add_wait_queue(q, wait);
> @@ -83,10 +81,9 @@ prepare_to_wait_exclusive(wait_queue_head_t *q, wait_queue_t *wait, int state)
> {
> unsigned long flags;
>
> - wait->flags |= WQ_FLAG_EXCLUSIVE;
> spin_lock_irqsave(&q->lock, flags);
> if (list_empty(&wait->task_list))
> - __add_wait_queue_tail(q, wait);
> + __add_wait_queue_ex(q, wait);
> set_current_state(state);
> spin_unlock_irqrestore(&q->lock, flags);
> }
> --
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