[PATCH 4/7] preempt, locking: Rework local_bh_{dis,en}able()

Peter Zijlstra
2013-11-20T16:34:48Z

[-- Attachment #1: peter_zijlstra-inline-local_bh_disable.patch --]
[-- Type: text/plain, Size: 4831 bytes --]

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.

Cc: rjw@rjwysocki.net
Cc: rui.zhang@intel.com
Cc: jacob.jun.pan@linux.intel.com
Cc: Mike Galbraith <bitbucket@online.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: hpa@zytor.com
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: lenb@kernel.org
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
---
include/linux/bottom_half.h | 32 +++++++++++++++++++++++++++++---
include/linux/hardirq.h | 1 +
include/linux/preempt_mask.h | 1 -
kernel/softirq.c | 33 ++++-----------------------------
4 files changed, 34 insertions(+), 33 deletions(-)

--- 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 +114,8 @@ 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();
-}
#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 +138,7 @@ 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 +153,7 @@ 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())) {
/*
@@ -183,18 +170,6 @@ static inline void _local_bh_enable_ip(u
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);
-
/*
* We restart softirq processing for at most MAX_SOFTIRQ_RESTART times,
* but break the loop if need_resched() is set or after 2 ms.
@@ -268,7 +243,7 @@ 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();