Re: [PATCH 2/2] wait: introduce prepare_to_wait_event()

[Oleg Nesterov <oleg@redhat.com>]

Hi Tejun,

On 06/06, Tejun Heo wrote:
>
> Which tree are the patches based on?  I'm getting conflicts on
> linus#master, mmotd and next.

Hmm. linus#master. I just verified that the patches apply cleanly
after git-pull.

> Reviewed-by: Tejun Heo <tj@kernel.org>

Thanks,

> But a couple nits.
>
> > +int
>
> I don't think we need to keep the unnecessary line break here.  All
> other functions in the file don't do it except for the two
> prepare_to_wait functions.  No need to give the weirdos more power. :)

Yes, I tried to follow the style around the new helper, but the extra
line is not needed.

Please see v2 below, no other changes.

> > +prepare_to_wait_event(wait_queue_head_t *q, wait_queue_t *wait, int state)
> > +{
> > +	if (signal_pending_state(state, current))
> > +		return -ERESTARTSYS;
> > +
> > +	wait->private = current;
> > +	wait->func = autoremove_wake_function;
> > +	prepare_to_wait(q, wait, state);
>
> I wonder whether it'd be worthwhile to make prepare_to_wait() inline
> so that it can be inlined into the above.  I think gcc is smart enough
> to emit inline for in-file stuff and then build a proper function for
> external references.  No biggie.  Just wondering.

Not sure... As you can see from this patch, I like -Os more than -O2 ;)


------------------------------------------------------------------------------
Subject: [PATCH v2 2/2] wait: introduce prepare_to_wait_event()

Add the new helper, prepare_to_wait_event() which should only be used
by wait_event_common/etc.

prepare_to_wait_event() returns -ERESTARTSYS if signal_pending_state()
is true, otherwise it calls prepare_to_wait(). This allows to uninline
the signal-pending checks in wait_event_*.

Also, it can initialize wait->private/func. We do not care they were
already initialized, the values are the same. This also shaves a couple
of insns from the inlined code.

Unlike the previous change, this patch "reliably" shrinks the size of
generated code for every wait_event*() call.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Tejun Heo <tj@kernel.org>
---
 include/linux/wait.h |   22 +++++++++++-----------
 kernel/wait.c        |   13 +++++++++++++
 2 files changed, 24 insertions(+), 11 deletions(-)

diff --git a/include/linux/wait.h b/include/linux/wait.h
index 392c54d..a2314dd 100644
--- a/include/linux/wait.h
+++ b/include/linux/wait.h
@@ -176,28 +176,27 @@ wait_queue_head_t *bit_waitqueue(void *, int);
 #define __wait_no_timeout(tout)	\
 	(__builtin_constant_p(tout) && (tout) == MAX_SCHEDULE_TIMEOUT)
 
-/* uglified signal_pending_state() optimized for constant state */
-#define __wait_signal_pending(state)					\
-	((state == TASK_INTERRUPTIBLE) ? signal_pending(current) :	\
-	 (state == TASK_KILLABLE) ? fatal_signal_pending(current) :	\
-	  0)
+#define __wait_interruptible(state)					\
+	(!__builtin_constant_p(state) ||				\
+	 	state == TASK_INTERRUPTIBLE || state == TASK_KILLABLE)
 
 #define __wait_event_common(wq, condition, state, tout)			\
 ({									\
-	DEFINE_WAIT(__wait);						\
-	long __ret = 0, __tout = tout;					\
+	long __ret, __tout = tout;					\
+	wait_queue_t __wait;						\
+									\
+	INIT_LIST_HEAD(&__wait.task_list);				\
+	__wait.flags = 0;						\
 									\
 	for (;;) {							\
-		prepare_to_wait(&wq, &__wait, state);			\
+		__ret = prepare_to_wait_event(&wq, &__wait, state);	\
 		if (condition) {					\
 			__ret = __wait_no_timeout(tout) ?: __tout ?: 1;	\
 			break;						\
 		}							\
 									\
-		if (__wait_signal_pending(state)) {			\
-			__ret = -ERESTARTSYS;				\
+		if (__wait_interruptible(state) && __ret)		\
 			break;						\
-		}							\
 									\
 		if (__wait_no_timeout(tout))				\
 			schedule();					\
@@ -781,6 +780,7 @@ extern long interruptible_sleep_on_timeout(wait_queue_head_t *q,
  * Waitqueues which are removed from the waitqueue_head at wakeup time
  */
 void prepare_to_wait(wait_queue_head_t *q, wait_queue_t *wait, int state);
+int prepare_to_wait_event(wait_queue_head_t *q, wait_queue_t *wait, int state);
 void prepare_to_wait_exclusive(wait_queue_head_t *q, wait_queue_t *wait, int state);
 void finish_wait(wait_queue_head_t *q, wait_queue_t *wait);
 void abort_exclusive_wait(wait_queue_head_t *q, wait_queue_t *wait,
diff --git a/kernel/wait.c b/kernel/wait.c
index 6698e0c..3b8619a 100644
--- a/kernel/wait.c
+++ b/kernel/wait.c
@@ -78,6 +78,19 @@ prepare_to_wait(wait_queue_head_t *q, wait_queue_t *wait, int state)
 }
 EXPORT_SYMBOL(prepare_to_wait);
 
+int prepare_to_wait_event(wait_queue_head_t *q, wait_queue_t *wait, int state)
+{
+	if (signal_pending_state(state, current))
+		return -ERESTARTSYS;
+
+	wait->private = current;
+	wait->func = autoremove_wake_function;
+	prepare_to_wait(q, wait, state);
+
+	return 0;
+}
+EXPORT_SYMBOL(prepare_to_wait_event);
+
 void
 prepare_to_wait_exclusive(wait_queue_head_t *q, wait_queue_t *wait, int state)
 {
-- 
1.5.5.1