linux-kernel - [RFC][PATCH]: wait: don't resched in prepare_to

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Date:	Fri, 06 Mar 2009 15:39:37 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	Oleg Nesterov <onestero@...hat.com>,
	Nick Piggin <npiggin@...e.de>
Cc:	lkml <linux-kernel@...r.kernel.org>
Subject: [RFC][PATCH]: wait: don't resched in prepare_to_wait()

Does the below make sense?

After prepare to wait, we either call schedule() or find !cond in which
case we'll call finish_wait() which contains another preemption check.

Not-signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
---
 kernel/wait.c |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/kernel/wait.c b/kernel/wait.c
index 42a2dbc..7b866ab 100644
--- a/kernel/wait.c
+++ b/kernel/wait.c
@@ -73,7 +73,9 @@ prepare_to_wait(wait_queue_head_t *q, wait_queue_t *wait, int state)
 	if (list_empty(&wait->task_list))
 		__add_wait_queue(q, wait);
 	set_current_state(state);
+	preempt_disable();
 	spin_unlock_irqrestore(&q->lock, flags);
+	preempt_enable_no_resched();
 }
 EXPORT_SYMBOL(prepare_to_wait);
 
@@ -87,7 +89,9 @@ prepare_to_wait_exclusive(wait_queue_head_t *q, wait_queue_t *wait, int state)
 	if (list_empty(&wait->task_list))
 		__add_wait_queue_tail(q, wait);
 	set_current_state(state);
+	preempt_disable();
 	spin_unlock_irqrestore(&q->lock, flags);
+	preempt_enable_no_resched();
 }
 EXPORT_SYMBOL(prepare_to_wait_exclusive);
 


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