[PATCH v3 13/13] irq: Optimize reschedule check in local_interrupt_enable()

[Boqun Feng]

In local_interrupt_enable(), we could avoid re-reading preempt count
because of should_resched() by using the result from
hardirq_disable_exit(), however this means __preempt_count_add_return()
and __preempt_count_sub_return() need to return all the preempt count
bits (including the PREEMPT_NEED_RESCHED bit), since the only user of
__preempt_count_{add,sub}_return() is hardirq_disable_{enter,exit}(),
hence make them return "unsigned long" to optimize this.

Signed-off-by: Boqun Feng <boqun@xxxxxxxxxx>
---
 arch/arm64/include/asm/preempt.h | 12 ++++++------
 arch/s390/include/asm/preempt.h  |  4 ++--
 arch/x86/include/asm/preempt.h   |  4 ++--
 include/asm-generic/preempt.h    |  4 ++--
 include/linux/interrupt_rc.h     | 31 ++++++++++++++++++++-----------
 5 files changed, 32 insertions(+), 23 deletions(-)

diff --git a/arch/arm64/include/asm/preempt.h b/arch/arm64/include/asm/preempt.h
index 0dd8221d1bef..e9f597d87413 100644
--- a/arch/arm64/include/asm/preempt.h
+++ b/arch/arm64/include/asm/preempt.h
@@ -55,20 +55,20 @@ static inline void __preempt_count_sub(int val)
 	WRITE_ONCE(current_thread_info()->preempt.count, pc);
 }
 
-static inline int __preempt_count_add_return(int val)
+static inline unsigned long __preempt_count_add_return(int val)
 {
-	u32 pc = READ_ONCE(current_thread_info()->preempt.count);
+	u64 pc = READ_ONCE(current_thread_info()->preempt_count);
 	pc += val;
-	WRITE_ONCE(current_thread_info()->preempt.count, pc);
+	WRITE_ONCE(current_thread_info()->preempt_count, pc);
 
 	return pc;
 }
 
-static inline int __preempt_count_sub_return(int val)
+static inline unsigned long __preempt_count_sub_return(int val)
 {
-	u32 pc = READ_ONCE(current_thread_info()->preempt.count);
+	u64 pc = READ_ONCE(current_thread_info()->preempt_count);
 	pc -= val;
-	WRITE_ONCE(current_thread_info()->preempt.count, pc);
+	WRITE_ONCE(current_thread_info()->preempt_count, pc);
 
 	return pc;
 }
diff --git a/arch/s390/include/asm/preempt.h b/arch/s390/include/asm/preempt.h
index 1d5e4d7e9e1b..d0021b979a5d 100644
--- a/arch/s390/include/asm/preempt.h
+++ b/arch/s390/include/asm/preempt.h
@@ -136,12 +136,12 @@ static __always_inline bool should_resched(int preempt_offset)
 	return unlikely(READ_ONCE(get_lowcore()->preempt_count) == preempt_offset);
 }
 
-static __always_inline int __preempt_count_add_return(int val)
+static __always_inline unsigned long __preempt_count_add_return(int val)
 {
 	return val + __atomic64_add(val, (long *)&get_lowcore()->preempt_count);
 }
 
-static __always_inline int __preempt_count_sub_return(int val)
+static __always_inline unsigned long __preempt_count_sub_return(int val)
 {
 	return __preempt_count_add_return(-val);
 }
diff --git a/arch/x86/include/asm/preempt.h b/arch/x86/include/asm/preempt.h
index 12353eeebc52..fc1a2799990a 100644
--- a/arch/x86/include/asm/preempt.h
+++ b/arch/x86/include/asm/preempt.h
@@ -103,12 +103,12 @@ static __always_inline void __preempt_count_sub(int val)
 	__pc_op(add, __preempt_count, -val);
 }
 
-static __always_inline int __preempt_count_add_return(int val)
+static __always_inline unsigned long __preempt_count_add_return(int val)
 {
 	return __pc_op(add_return, __preempt_count, val);
 }
 
-static __always_inline int __preempt_count_sub_return(int val)
+static __always_inline unsigned long __preempt_count_sub_return(int val)
 {
 	return __pc_op(add_return, __preempt_count, -val);
 }
diff --git a/include/asm-generic/preempt.h b/include/asm-generic/preempt.h
index c8683c046615..7629e23102d1 100644
--- a/include/asm-generic/preempt.h
+++ b/include/asm-generic/preempt.h
@@ -59,14 +59,14 @@ static __always_inline void __preempt_count_sub(int val)
 	*preempt_count_ptr() -= val;
 }
 
-static __always_inline int __preempt_count_add_return(int val)
+static __always_inline unsigned long __preempt_count_add_return(int val)
 {
 	*preempt_count_ptr() += val;
 
 	return *preempt_count_ptr();
 }
 
-static __always_inline int __preempt_count_sub_return(int val)
+static __always_inline unsigned long __preempt_count_sub_return(int val)
 {
 	*preempt_count_ptr() -= val;
 
diff --git a/include/linux/interrupt_rc.h b/include/linux/interrupt_rc.h
index dd4444c61330..c044dc395452 100644
--- a/include/linux/interrupt_rc.h
+++ b/include/linux/interrupt_rc.h
@@ -27,7 +27,7 @@ DECLARE_PER_CPU(struct interrupt_disable_state, local_interrupt_disable_state);
 static inline void local_interrupt_disable(void)
 {
 	unsigned long flags;
-	int new_count;
+	unsigned long new_count;
 
 	WARN_ON_ONCE(in_nmi());
 
@@ -41,9 +41,25 @@ static inline void local_interrupt_disable(void)
 	}
 }
 
+#ifdef CONFIG_PREEMPTION
+static inline void local_interrupt_enable_reched(unsigned long pc)
+{
+	if (pc)
+		return;
+	/* No PREEMPT_NEED_RESCHED bit? Check tif_need_resched() */
+#ifndef PREEMPT_NEED_RESCHED
+	if (!tif_need_resched())
+		return;
+#endif
+	__preempt_schedule();
+}
+#else
+static inline void local_interrupt_enable_reched(unsigned long pc) {}
+#endif
+
 static inline void local_interrupt_enable(void)
 {
-	int new_count;
+	unsigned long new_count;
 
 	new_count = hardirq_disable_exit();
 
@@ -52,15 +68,8 @@ static inline void local_interrupt_enable(void)
 
 		flags = raw_cpu_read(local_interrupt_disable_state.flags);
 		local_irq_restore(flags);
-		/*
-		 * TODO: re-read preempt count can be avoided, but it needs
-		 * should_resched() taking another parameter as the current
-		 * preempt count
-		 */
-#ifdef CONFIG_PREEMPTION
-		if (should_resched(0))
-			__preempt_schedule();
-#endif
+
+		local_interrupt_enable_reched(new_count);
 	}
 }
 
-- 
2.51.0