linux-kernel - [PATCH 4/7] preempt: Disable preemption from preempt

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Message-Id: <1431356904-4624-5-git-send-email-fweisbec@gmail.com>
Date:	Mon, 11 May 2015 17:08:21 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 4/7] preempt: Disable preemption from preempt_schedule*() callers

Lets gather the preempt operations (set PREEMPT_ACTIVE and disable
preemption) in a single operation. This way we prepare to remove the
preemption disablement in __schedule() in order to omptimize this
duty on the caller.

Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
---
 include/linux/preempt.h | 12 ++++++++++++
 kernel/sched/core.c     | 20 ++++++--------------
 2 files changed, 18 insertions(+), 14 deletions(-)

diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index 4689ef2..45da394 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -137,6 +137,18 @@ extern void preempt_count_sub(int val);
 #define preempt_count_inc() preempt_count_add(1)
 #define preempt_count_dec() preempt_count_sub(1)
 
+#define preempt_active_enter() \
+do { \
+	preempt_count_add(PREEMPT_ACTIVE + PREEMPT_DISABLE_OFFSET); \
+	barrier(); \
+} while (0)
+
+#define preempt_active_exit() \
+do { \
+	barrier(); \
+	preempt_count_sub(PREEMPT_ACTIVE + PREEMPT_DISABLE_OFFSET); \
+} while (0)
+
 #ifdef CONFIG_PREEMPT_COUNT
 
 #define preempt_disable() \
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 8027cfd..182127a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2859,15 +2859,14 @@ void __sched schedule_preempt_disabled(void)
 static void __sched notrace preempt_schedule_common(void)
 {
 	do {
-		__preempt_count_add(PREEMPT_ACTIVE);
+		preempt_active_enter();
 		__schedule();
-		__preempt_count_sub(PREEMPT_ACTIVE);
+		preempt_active_exit();
 
 		/*
 		 * Check again in case we missed a preemption opportunity
 		 * between schedule and now.
 		 */
-		barrier();
 	} while (need_resched());
 }
 
@@ -2914,7 +2913,7 @@ asmlinkage __visible void __sched notrace preempt_schedule_context(void)
 		return;
 
 	do {
-		__preempt_count_add(PREEMPT_ACTIVE);
+		preempt_active_enter();
 		/*
 		 * Needs preempt disabled in case user_exit() is traced
 		 * and the tracer calls preempt_enable_notrace() causing
@@ -2924,8 +2923,7 @@ asmlinkage __visible void __sched notrace preempt_schedule_context(void)
 		__schedule();
 		exception_exit(prev_ctx);
 
-		__preempt_count_sub(PREEMPT_ACTIVE);
-		barrier();
+		preempt_active_exit();
 	} while (need_resched());
 }
 EXPORT_SYMBOL_GPL(preempt_schedule_context);
@@ -2949,17 +2947,11 @@ asmlinkage __visible void __sched preempt_schedule_irq(void)
 	prev_state = exception_enter();
 
 	do {
-		__preempt_count_add(PREEMPT_ACTIVE);
+		preempt_active_enter();
 		local_irq_enable();
 		__schedule();
 		local_irq_disable();
-		__preempt_count_sub(PREEMPT_ACTIVE);
-
-		/*
-		 * Check again in case we missed a preemption opportunity
-		 * between schedule and now.
-		 */
-		barrier();
+		preempt_active_exit();
 	} while (need_resched());
 
 	exception_exit(prev_state);
-- 
2.1.4

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