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Message-ID: <20140608114052.GA8774@amd.pavel.ucw.cz>
Date: Sun, 8 Jun 2014 13:40:52 +0200
From: Pavel Machek <pavel@....cz>
To: Linus Torvalds <torvalds@...ux-foundation.org>,
kernel list <linux-kernel@...r.kernel.org>
Subject: per-thread wait_queue_t
Hi!
When you proposed to put wait queues into task_struct, you were
probably looking for less coding and more analysis?
Anyway, there's starter patch below... It compiles, but is otherwise
completely untested.
Signed-off-by: Pavel Machek <pavel@....cz>
Pavel
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index af90312..6dde102 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1591,7 +1591,7 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events,
int res = 0, eavail, timed_out = 0;
unsigned long flags;
long slack = 0;
- wait_queue_t wait;
+ wait_queue_t *wait;
ktime_t expires, *to = NULL;
if (timeout > 0) {
@@ -1614,13 +1614,14 @@ fetch_events:
spin_lock_irqsave(&ep->lock, flags);
if (!ep_events_available(ep)) {
+ wait = alloc_waitqueue(GFP_KERNEL);
/*
* We don't have any available event to return to the caller.
* We need to sleep here, and we will be wake up by
* ep_poll_callback() when events will become available.
*/
- init_waitqueue_entry(&wait, current);
- __add_wait_queue_exclusive(&ep->wq, &wait);
+ init_waitqueue_entry(wait, current);
+ __add_wait_queue_exclusive(&ep->wq, wait);
for (;;) {
/*
@@ -1642,7 +1643,8 @@ fetch_events:
spin_lock_irqsave(&ep->lock, flags);
}
- __remove_wait_queue(&ep->wq, &wait);
+ __remove_wait_queue(&ep->wq, wait);
+ free_waitqueue(wait);
set_current_state(TASK_RUNNING);
}
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 25f54c7..0b2be71 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -26,6 +26,7 @@ struct sched_param {
#include <linux/nodemask.h>
#include <linux/mm_types.h>
#include <linux/preempt_mask.h>
+#include <linux/slab.h>
#include <asm/page.h>
#include <asm/ptrace.h>
@@ -1607,6 +1608,8 @@ struct task_struct {
unsigned int sequential_io;
unsigned int sequential_io_avg;
#endif
+
+ wait_queue_t wait_queues[NUM_TASK_WAIT_QUEUES];
};
/* Future-safe accessor for struct task_struct's cpus_allowed. */
@@ -2991,4 +2994,26 @@ static inline unsigned long rlimit_max(unsigned int limit)
return task_rlimit_max(current, limit);
}
+static inline wait_queue_t *alloc_waitqueue(int gfp)
+{
+ int i;
+ for (i=0; i<NUM_TASK_WAIT_QUEUES; i++) {
+ if (current->wait_queues[i].flags & WQ_FLAG_FREE) {
+ current->wait_queues[i].flags &= ~WQ_FLAG_FREE;
+ return ¤t->wait_queues[i];
+ }
+ }
+ return kmalloc(sizeof(wait_queue_t), gfp);
+}
+
+static inline void free_waitqueue(wait_queue_t *q)
+{
+ if (q->flags & WQ_FLAG_HARDCODED) {
+ q->flags |= WQ_FLAG_FREE;
+ return;
+ }
+ kfree(q);
+}
+
+
#endif
diff --git a/include/linux/wait.h b/include/linux/wait.h
index bd68819..6c0dd83 100644
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -16,11 +16,15 @@ int default_wake_function(wait_queue_t *wait, unsigned mode, int flags, void *ke
struct __wait_queue {
unsigned int flags;
#define WQ_FLAG_EXCLUSIVE 0x01
+#define WQ_FLAG_FREE 0x02
+#define WQ_FLAG_HARDCODED 0x04
void *private;
wait_queue_func_t func;
struct list_head task_list;
};
+#define NUM_TASK_WAIT_QUEUES 2
+
struct wait_bit_key {
void *flags;
int bit_nr;
@@ -83,6 +87,7 @@ extern void __init_waitqueue_head(wait_queue_head_t *q, const char *name, struct
# define DECLARE_WAIT_QUEUE_HEAD_ONSTACK(name) DECLARE_WAIT_QUEUE_HEAD(name)
#endif
+
static inline void init_waitqueue_entry(wait_queue_t *q, struct task_struct *p)
{
q->flags = 0;
diff --git a/kernel/fork.c b/kernel/fork.c
index 54a8d26..c339e18 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1315,6 +1315,13 @@ static struct task_struct *copy_process(unsigned long clone_flags,
p->sequential_io = 0;
p->sequential_io_avg = 0;
#endif
+ {
+ int i;
+ for (i=0; i<NUM_TASK_WAIT_QUEUES; i++) {
+ init_waitqueue_entry(&p->wait_queues[i], p);
+ p->wait_queues[i].flags = WQ_FLAG_FREE | WQ_FLAG_HARDCODED;
+ }
+ }
/* Perform scheduler related setup. Assign this task to a CPU. */
retval = sched_fork(clone_flags, p);
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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