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Date: Wed, 30 Mar 2016 16:53:05 +0200
From: Daniel Wagner <wagi@...om.org>
To: linux-kernel@...r.kernel.org, linux-rt-users@...r.kernel.org
Cc: "Peter Zijlstra (Intel)" <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Daniel Wagner <daniel.wagner@...-carit.de>
Subject: [RFC v1] sched/completion: convert completions to use simple wait queues
From: Daniel Wagner <daniel.wagner@...-carit.de>
Completions have no long lasting callbacks and therefore do not need
the complex waitqueue variant. Use simple waitqueues which reduces
the contention on the waitqueue lock.
This was a carry forward from v3.10-rt, with some RT specific chunks,
dropped, and updated to align with names that were chosen to match the
simple waitqueue support.
[wagi: Added flag to defer swake_up_all() from irq context]
Signed-off-by: Daniel Wagner <daniel.wagner@...-carit.de>
---
include/linux/completion.h | 23 ++++++++++++++++-------
include/linux/swait.h | 1 +
kernel/sched/completion.c | 43 ++++++++++++++++++++++++++-----------------
kernel/sched/swait.c | 24 ++++++++++++++++++++++++
4 files changed, 67 insertions(+), 24 deletions(-)
diff --git a/include/linux/completion.h b/include/linux/completion.h
index 5d5aaae..45fd91a 100644
--- a/include/linux/completion.h
+++ b/include/linux/completion.h
@@ -8,7 +8,7 @@
* See kernel/sched/completion.c for details.
*/
-#include <linux/wait.h>
+#include <linux/swait.h>
/*
* struct completion - structure used to maintain state for a "completion"
@@ -22,13 +22,22 @@
* reinit_completion(), and macros DECLARE_COMPLETION(),
* DECLARE_COMPLETION_ONSTACK().
*/
+
+#define COMPLETION_DEFER (1 << 0)
+
struct completion {
- unsigned int done;
- wait_queue_head_t wait;
+ union {
+ struct {
+ unsigned short flags;
+ unsigned short done;
+ };
+ unsigned int val;
+ };
+ struct swait_queue_head wait;
};
#define COMPLETION_INITIALIZER(work) \
- { 0, __WAIT_QUEUE_HEAD_INITIALIZER((work).wait) }
+ { 0, 0, __SWAIT_QUEUE_HEAD_INITIALIZER((work).wait) }
#define COMPLETION_INITIALIZER_ONSTACK(work) \
({ init_completion(&work); work; })
@@ -72,8 +81,8 @@ struct completion {
*/
static inline void init_completion(struct completion *x)
{
- x->done = 0;
- init_waitqueue_head(&x->wait);
+ x->val = 0;
+ init_swait_queue_head(&x->wait);
}
/**
@@ -85,7 +94,7 @@ static inline void init_completion(struct completion *x)
*/
static inline void reinit_completion(struct completion *x)
{
- x->done = 0;
+ x->val = 0;
}
extern void wait_for_completion(struct completion *);
diff --git a/include/linux/swait.h b/include/linux/swait.h
index c1f9c62..83f004a 100644
--- a/include/linux/swait.h
+++ b/include/linux/swait.h
@@ -87,6 +87,7 @@ static inline int swait_active(struct swait_queue_head *q)
extern void swake_up(struct swait_queue_head *q);
extern void swake_up_all(struct swait_queue_head *q);
extern void swake_up_locked(struct swait_queue_head *q);
+extern void swake_up_all_locked(struct swait_queue_head *q);
extern void __prepare_to_swait(struct swait_queue_head *q, struct swait_queue *wait);
extern void prepare_to_swait(struct swait_queue_head *q, struct swait_queue *wait, int state);
diff --git a/kernel/sched/completion.c b/kernel/sched/completion.c
index 8d0f35d..d4dccd3 100644
--- a/kernel/sched/completion.c
+++ b/kernel/sched/completion.c
@@ -30,10 +30,10 @@ void complete(struct completion *x)
{
unsigned long flags;
- spin_lock_irqsave(&x->wait.lock, flags);
+ raw_spin_lock_irqsave(&x->wait.lock, flags);
x->done++;
- __wake_up_locked(&x->wait, TASK_NORMAL, 1);
- spin_unlock_irqrestore(&x->wait.lock, flags);
+ swake_up_locked(&x->wait);
+ raw_spin_unlock_irqrestore(&x->wait.lock, flags);
}
EXPORT_SYMBOL(complete);
@@ -50,10 +50,15 @@ void complete_all(struct completion *x)
{
unsigned long flags;
- spin_lock_irqsave(&x->wait.lock, flags);
- x->done += UINT_MAX/2;
- __wake_up_locked(&x->wait, TASK_NORMAL, 0);
- spin_unlock_irqrestore(&x->wait.lock, flags);
+ raw_spin_lock_irqsave(&x->wait.lock, flags);
+ x->done += USHRT_MAX/2;
+ if (irqs_disabled_flags(flags)) {
+ x->flags = COMPLETION_DEFER;
+ swake_up_locked(&x->wait);
+ } else {
+ swake_up_all_locked(&x->wait);
+ }
+ raw_spin_unlock_irqrestore(&x->wait.lock, flags);
}
EXPORT_SYMBOL(complete_all);
@@ -62,20 +67,20 @@ do_wait_for_common(struct completion *x,
long (*action)(long), long timeout, int state)
{
if (!x->done) {
- DECLARE_WAITQUEUE(wait, current);
+ DECLARE_SWAITQUEUE(wait);
- __add_wait_queue_tail_exclusive(&x->wait, &wait);
+ __prepare_to_swait(&x->wait, &wait);
do {
if (signal_pending_state(state, current)) {
timeout = -ERESTARTSYS;
break;
}
__set_current_state(state);
- spin_unlock_irq(&x->wait.lock);
+ raw_spin_unlock_irq(&x->wait.lock);
timeout = action(timeout);
- spin_lock_irq(&x->wait.lock);
+ raw_spin_lock_irq(&x->wait.lock);
} while (!x->done && timeout);
- __remove_wait_queue(&x->wait, &wait);
+ __finish_swait(&x->wait, &wait);
if (!x->done)
return timeout;
}
@@ -89,9 +94,13 @@ __wait_for_common(struct completion *x,
{
might_sleep();
- spin_lock_irq(&x->wait.lock);
+ raw_spin_lock_irq(&x->wait.lock);
timeout = do_wait_for_common(x, action, timeout, state);
- spin_unlock_irq(&x->wait.lock);
+ raw_spin_unlock_irq(&x->wait.lock);
+ if (x->flags & COMPLETION_DEFER) {
+ x->flags = 0;
+ swake_up_all(&x->wait);
+ }
return timeout;
}
@@ -277,12 +286,12 @@ bool try_wait_for_completion(struct completion *x)
if (!READ_ONCE(x->done))
return 0;
- spin_lock_irqsave(&x->wait.lock, flags);
+ raw_spin_lock_irqsave(&x->wait.lock, flags);
if (!x->done)
ret = 0;
else
x->done--;
- spin_unlock_irqrestore(&x->wait.lock, flags);
+ raw_spin_unlock_irqrestore(&x->wait.lock, flags);
return ret;
}
EXPORT_SYMBOL(try_wait_for_completion);
@@ -311,7 +320,7 @@ bool completion_done(struct completion *x)
* after it's acquired the lock.
*/
smp_rmb();
- spin_unlock_wait(&x->wait.lock);
+ raw_spin_unlock_wait(&x->wait.lock);
return true;
}
EXPORT_SYMBOL(completion_done);
diff --git a/kernel/sched/swait.c b/kernel/sched/swait.c
index 82f0dff..efe366b 100644
--- a/kernel/sched/swait.c
+++ b/kernel/sched/swait.c
@@ -72,6 +72,30 @@ void swake_up_all(struct swait_queue_head *q)
}
EXPORT_SYMBOL(swake_up_all);
+void swake_up_all_locked(struct swait_queue_head *q)
+{
+ struct swait_queue *curr;
+ LIST_HEAD(tmp);
+
+ if (!swait_active(q))
+ return;
+
+ list_splice_init(&q->task_list, &tmp);
+ while (!list_empty(&tmp)) {
+ curr = list_first_entry(&tmp, typeof(*curr), task_list);
+
+ wake_up_state(curr->task, TASK_NORMAL);
+ list_del_init(&curr->task_list);
+
+ if (list_empty(&tmp))
+ break;
+
+ raw_spin_unlock_irq(&q->lock);
+ raw_spin_lock_irq(&q->lock);
+ }
+}
+EXPORT_SYMBOL(swake_up_all_locked);
+
void __prepare_to_swait(struct swait_queue_head *q, struct swait_queue *wait)
{
wait->task = current;
--
2.5.5
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