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Subject[patch, BK-curr] nonintrusive spin-polling loop in kernel/spinlock.c

this patch, against BK-curr, implements a nonintrusive spin-polling loop
for the SMP+PREEMPT spinlock/rwlock variants, using the new *_can_lock()
primitives. (The patch also adds *_can_lock() to the UP branch of
spinlock.h, for completeness.)

build- and boot-tested on x86 SMP+PREEMPT and SMP+!PREEMPT.

Ingo

Signed-off-by: Ingo Molnar <mingo@elte.hu>

--- linux/kernel/spinlock.c.orig
+++ linux/kernel/spinlock.c
@@ -174,7 +174,7 @@ EXPORT_SYMBOL(_write_lock);
*/

#define BUILD_LOCK_OPS(op, locktype) \
-void __lockfunc _##op##_lock(locktype *lock) \
+void __lockfunc _##op##_lock(locktype##_t *lock) \
{ \
preempt_disable(); \
for (;;) { \
@@ -183,14 +183,15 @@ void __lockfunc _##op##_lock(locktype *l
preempt_enable(); \
if (!(lock)->break_lock) \
(lock)->break_lock = 1; \
- cpu_relax(); \
+ while (!op##_can_lock(lock) && (lock)->break_lock) \
+ cpu_relax(); \
preempt_disable(); \
} \
} \
\
EXPORT_SYMBOL(_##op##_lock); \
\
-unsigned long __lockfunc _##op##_lock_irqsave(locktype *lock) \
+unsigned long __lockfunc _##op##_lock_irqsave(locktype##_t *lock) \
{ \
unsigned long flags; \
\
@@ -204,7 +205,8 @@ unsigned long __lockfunc _##op##_lock_ir
preempt_enable(); \
if (!(lock)->break_lock) \
(lock)->break_lock = 1; \
- cpu_relax(); \
+ while (!op##_can_lock(lock) && (lock)->break_lock) \
+ cpu_relax(); \
preempt_disable(); \
} \
return flags; \
@@ -212,14 +214,14 @@ unsigned long __lockfunc _##op##_lock_ir
\
EXPORT_SYMBOL(_##op##_lock_irqsave); \
\
-void __lockfunc _##op##_lock_irq(locktype *lock) \
+void __lockfunc _##op##_lock_irq(locktype##_t *lock) \
{ \
_##op##_lock_irqsave(lock); \
} \
\
EXPORT_SYMBOL(_##op##_lock_irq); \
\
-void __lockfunc _##op##_lock_bh(locktype *lock) \
+void __lockfunc _##op##_lock_bh(locktype##_t *lock) \
{ \
unsigned long flags; \
\
@@ -244,9 +246,9 @@ EXPORT_SYMBOL(_##op##_lock_bh)
* _[spin|read|write]_lock_irqsave()
* _[spin|read|write]_lock_bh()
*/
-BUILD_LOCK_OPS(spin, spinlock_t);
-BUILD_LOCK_OPS(read, rwlock_t);
-BUILD_LOCK_OPS(write, rwlock_t);
+BUILD_LOCK_OPS(spin, spinlock);
+BUILD_LOCK_OPS(read, rwlock);
+BUILD_LOCK_OPS(write, rwlock);

#endif /* CONFIG_PREEMPT */

--- linux/include/linux/spinlock.h.orig
+++ linux/include/linux/spinlock.h
@@ -221,6 +221,8 @@ typedef struct {
#define _raw_read_unlock(lock) do { (void)(lock); } while(0)
#define _raw_write_lock(lock) do { (void)(lock); } while(0)
#define _raw_write_unlock(lock) do { (void)(lock); } while(0)
+#define read_can_lock(lock) (((void)(lock), 1))
+#define write_can_lock(lock) (((void)(lock), 1))
#define _raw_read_trylock(lock) ({ (void)(lock); (1); })
#define _raw_write_trylock(lock) ({ (void)(lock); (1); })

-
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