[4/8] preempt, locking: Rework local_bh_{dis,en}able()

Commit Message

Peter Zijlstra Nov. 26, 2013, 3:57 p.m. UTC

Currently local_bh_disable() is out-of-line for no apparent reason.
So inline it to save a few cycles on call/return nonsense, the
function body is a single add on x86 (a few loads and store extra on
load/store archs).

Also expose two new local_bh functions:

  __local_bh_{dis,en}able_ip(unsigned long ip, unsigned int cnt);

Which implement the actual local_bh_{dis,en}able() behaviour.

The next patch uses the exposed @cnt argument to optimize bh lock
functions.

With build fixes from Jacob Pan.

Cc: Arjan van de Ven <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: Mike Galbraith <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: [e-mail]
Reviewed-by: Thomas Gleixner <[e-mail]>
Signed-off-by: Peter Zijlstra <[e-mail]>
---
 include/linux/bottom_half.h  |   32 +++++++++++++++++++++++++++++---
 include/linux/hardirq.h      |    1 +
 include/linux/preempt_mask.h |    1 -
 kernel/softirq.c             |   35 ++++++-----------------------------
 4 files changed, 36 insertions(+), 33 deletions(-)



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Patch

--- a/include/linux/bottom_half.h
+++ b/include/linux/bottom_half.h
@@ -1,9 +1,35 @@ 
 #ifndef _LINUX_BH_H
 #define _LINUX_BH_H
 
-extern void local_bh_disable(void);
+#include <linux/preempt.h>
+#include <linux/preempt_mask.h>
+
+#ifdef CONFIG_TRACE_IRQFLAGS
+extern void __local_bh_disable_ip(unsigned long ip, unsigned int cnt);
+#else
+static __always_inline void __local_bh_disable_ip(unsigned long ip, unsigned int cnt)
+{
+	preempt_count_add(cnt);
+	barrier();
+}
+#endif
+
+static inline void local_bh_disable(void)
+{
+	__local_bh_disable_ip(_THIS_IP_, SOFTIRQ_DISABLE_OFFSET);
+}
+
 extern void _local_bh_enable(void);
-extern void local_bh_enable(void);
-extern void local_bh_enable_ip(unsigned long ip);
+extern void __local_bh_enable_ip(unsigned long ip, unsigned int cnt);
+
+static inline void local_bh_enable_ip(unsigned long ip)
+{
+	__local_bh_enable_ip(ip, SOFTIRQ_DISABLE_OFFSET);
+}
+
+static inline void local_bh_enable(void)
+{
+	__local_bh_enable_ip(_THIS_IP_, SOFTIRQ_DISABLE_OFFSET);
+}
 
 #endif /* _LINUX_BH_H */
--- a/include/linux/hardirq.h
+++ b/include/linux/hardirq.h
@@ -5,6 +5,7 @@ 
 #include <linux/lockdep.h>
 #include <linux/ftrace_irq.h>
 #include <linux/vtime.h>
+#include <asm/hardirq.h>
 
 
 extern void synchronize_irq(unsigned int irq);
--- a/include/linux/preempt_mask.h
+++ b/include/linux/preempt_mask.h
@@ -2,7 +2,6 @@ 
 #define LINUX_PREEMPT_MASK_H
 
 #include <linux/preempt.h>
-#include <asm/hardirq.h>
 
 /*
  * We put the hardirq and softirq counter into the preemption
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -89,7 +89,7 @@  static void wakeup_softirqd(void)
  * where hardirqs are disabled legitimately:
  */
 #ifdef CONFIG_TRACE_IRQFLAGS
-static void __local_bh_disable(unsigned long ip, unsigned int cnt)
+void __local_bh_disable_ip(unsigned long ip, unsigned int cnt)
 {
 	unsigned long flags;
 
@@ -114,21 +114,9 @@  static void __local_bh_disable(unsigned
 	if (preempt_count() == cnt)
 		trace_preempt_off(CALLER_ADDR0, get_parent_ip(CALLER_ADDR1));
 }
-#else /* !CONFIG_TRACE_IRQFLAGS */
-static inline void __local_bh_disable(unsigned long ip, unsigned int cnt)
-{
-	preempt_count_add(cnt);
-	barrier();
-}
+EXPORT_SYMBOL(__local_bh_disable_ip);
 #endif /* CONFIG_TRACE_IRQFLAGS */
 
-void local_bh_disable(void)
-{
-	__local_bh_disable(_RET_IP_, SOFTIRQ_DISABLE_OFFSET);
-}
-
-EXPORT_SYMBOL(local_bh_disable);
-
 static void __local_bh_enable(unsigned int cnt)
 {
 	WARN_ON_ONCE(!irqs_disabled());
@@ -151,7 +139,7 @@  void _local_bh_enable(void)
 
 EXPORT_SYMBOL(_local_bh_enable);
 
-static inline void _local_bh_enable_ip(unsigned long ip)
+void __local_bh_enable_ip(unsigned long ip, unsigned int cnt)
 {
 	WARN_ON_ONCE(in_irq() || irqs_disabled());
 #ifdef CONFIG_TRACE_IRQFLAGS
@@ -166,7 +154,7 @@  static inline void _local_bh_enable_ip(u
 	 * Keep preemption disabled until we are done with
 	 * softirq processing:
  	 */
-	preempt_count_sub(SOFTIRQ_DISABLE_OFFSET - 1);
+	preempt_count_sub(cnt - 1);
 
 	if (unlikely(!in_interrupt() && local_softirq_pending())) {
 		/*
@@ -182,18 +170,7 @@  static inline void _local_bh_enable_ip(u
 #endif
 	preempt_check_resched();
 }
-
-void local_bh_enable(void)
-{
-	_local_bh_enable_ip(_RET_IP_);
-}
-EXPORT_SYMBOL(local_bh_enable);
-
-void local_bh_enable_ip(unsigned long ip)
-{
-	_local_bh_enable_ip(ip);
-}
-EXPORT_SYMBOL(local_bh_enable_ip);
+EXPORT_SYMBOL(__local_bh_enable_ip);
 
 /*
  * We restart softirq processing for at most MAX_SOFTIRQ_RESTART times,
@@ -268,7 +245,7 @@  asmlinkage void __do_softirq(void)
 	pending = local_softirq_pending();
 	account_irq_enter_time(current);
 
-	__local_bh_disable(_RET_IP_, SOFTIRQ_OFFSET);
+	__local_bh_disable_ip(_RET_IP_, SOFTIRQ_OFFSET);
 	lockdep_softirq_start();
 
 	cpu = smp_processor_id();