There seems to be no good reason for spin_lock_irq to disable interrupts
while spinning. Zwane Mwaikambo had an implementation couple of years ago,
and the only objection seemed to be concerns about buggy code using
spin_lock_irq whilst interrupts disabled
http://lkml.org/lkml/2004/5/26/87
That shouldn't be a concern anymore. Besides, spin_lock_irqsave now enables
interrupts while spinning.
As to the motivation, on a Sun x4600 8 socket 16 core x86_64 NUMA box,
we notice softlockups and quite a few lost timer ticks under extreme
memory pressure. The reason turned out to be that zone->lru_lock tends
to get heavily contended, and NUMA nodes try to grab the locks using
spin_lock_irq. Instrumentation showed us that interrupt hold offs can
last for a few seconds, and even the main timer interrupts get held off for
long -- which is not good. Enabling interrupts for spinlocks while spinning
made the machine responsive and the softlockups/lost ticks went away.
Although the scenario above was an extreme condition (very high memory
pressure), I guess it still makes sense to enable interrupts while spinning
for a lock.
The following patches do just that. The first patch is preparatory in nature
and the second one changes the x86_64 implementation of spin_lock_irq.
Patch passed overnight runs of kernbench and dbench on 4 way x86_64 smp.
Comments?
Thanks,
Kiran
Preparatory patch to enable interrupts while spinning with spinlock irqs.
Any arch which needs this feature just has to implement __raw_spin_lock_irq
Signed-off by: Pravin B. Shelar <[email protected]>
Signed-off by: Ravikiran Thirumalai <[email protected]>
Signed-off by: Shai Fultheim <[email protected]>
Index: linux-2.6.20-rc1/include/asm-alpha/spinlock.h
===================================================================
--- linux-2.6.20-rc1.orig/include/asm-alpha/spinlock.h 2006-11-29 13:57:37.000000000 -0800
+++ linux-2.6.20-rc1/include/asm-alpha/spinlock.h 2006-12-28 17:18:32.132775000 -0800
@@ -13,6 +13,7 @@
*/
#define __raw_spin_lock_flags(lock, flags) __raw_spin_lock(lock)
+#define __raw_spin_lock_irq(lock) __raw_spin_lock(lock)
#define __raw_spin_is_locked(x) ((x)->lock != 0)
#define __raw_spin_unlock_wait(x) \
do { cpu_relax(); } while ((x)->lock)
Index: linux-2.6.20-rc1/include/asm-arm/spinlock.h
===================================================================
--- linux-2.6.20-rc1.orig/include/asm-arm/spinlock.h 2006-11-29 13:57:37.000000000 -0800
+++ linux-2.6.20-rc1/include/asm-arm/spinlock.h 2006-12-28 17:18:32.132775000 -0800
@@ -22,6 +22,7 @@
do { while (__raw_spin_is_locked(lock)) cpu_relax(); } while (0)
#define __raw_spin_lock_flags(lock, flags) __raw_spin_lock(lock)
+#define __raw_spin_lock_irq(lock, flags) __raw_spin_lock(lock)
static inline void __raw_spin_lock(raw_spinlock_t *lock)
{
Index: linux-2.6.20-rc1/include/asm-cris/arch-v32/spinlock.h
===================================================================
--- linux-2.6.20-rc1.orig/include/asm-cris/arch-v32/spinlock.h 2006-11-29 13:57:37.000000000 -0800
+++ linux-2.6.20-rc1/include/asm-cris/arch-v32/spinlock.h 2006-12-29 16:36:27.182954000 -0800
@@ -36,7 +36,7 @@ static inline void _raw_spin_lock_flags
{
_raw_spin_lock(lock);
}
-
+#define __raw_spin_lock_irq(lock) _raw_spin_lock(lock)
/*
* Read-write spinlocks, allowing multiple readers
* but only one writer.
Index: linux-2.6.20-rc1/include/asm-i386/spinlock.h
===================================================================
--- linux-2.6.20-rc1.orig/include/asm-i386/spinlock.h 2006-12-21 14:34:33.871573917 -0800
+++ linux-2.6.20-rc1/include/asm-i386/spinlock.h 2006-12-28 17:18:32.142775000 -0800
@@ -82,6 +82,7 @@ static inline void __raw_spin_lock_flags
CLI_STI_INPUT_ARGS
: "memory" CLI_STI_CLOBBERS);
}
+# define __raw_spin_lock_irq(lock) __raw_spin_lock(lock)
#endif
static inline int __raw_spin_trylock(raw_spinlock_t *lock)
Index: linux-2.6.20-rc1/include/asm-ia64/spinlock.h
===================================================================
--- linux-2.6.20-rc1.orig/include/asm-ia64/spinlock.h 2006-11-29 13:57:37.000000000 -0800
+++ linux-2.6.20-rc1/include/asm-ia64/spinlock.h 2006-12-28 17:18:32.142775000 -0800
@@ -87,7 +87,7 @@ __raw_spin_lock_flags (raw_spinlock_t *l
}
#define __raw_spin_lock(lock) __raw_spin_lock_flags(lock, 0)
-
+# define __raw_spin_lock_irq(lock) __raw_spin_lock(lock)
/* Unlock by doing an ordered store and releasing the cacheline with nta */
static inline void __raw_spin_unlock(raw_spinlock_t *x) {
barrier();
@@ -96,6 +96,7 @@ static inline void __raw_spin_unlock(raw
#else /* !ASM_SUPPORTED */
#define __raw_spin_lock_flags(lock, flags) __raw_spin_lock(lock)
+# define __raw_spin_lock_irq(lock) __raw_spin_lock(lock)
# define __raw_spin_lock(x) \
do { \
__u32 *ia64_spinlock_ptr = (__u32 *) (x); \
Index: linux-2.6.20-rc1/include/asm-m32r/spinlock.h
===================================================================
--- linux-2.6.20-rc1.orig/include/asm-m32r/spinlock.h 2006-11-29 13:57:37.000000000 -0800
+++ linux-2.6.20-rc1/include/asm-m32r/spinlock.h 2006-12-28 17:18:32.142775000 -0800
@@ -26,6 +26,7 @@
#define __raw_spin_is_locked(x) (*(volatile int *)(&(x)->slock) <= 0)
#define __raw_spin_lock_flags(lock, flags) __raw_spin_lock(lock)
+#define __raw_spin_lock_irq(lock) __raw_spin_lock(lock)
#define __raw_spin_unlock_wait(x) \
do { cpu_relax(); } while (__raw_spin_is_locked(x))
Index: linux-2.6.20-rc1/include/asm-mips/spinlock.h
===================================================================
--- linux-2.6.20-rc1.orig/include/asm-mips/spinlock.h 2006-12-21 14:34:34.641585532 -0800
+++ linux-2.6.20-rc1/include/asm-mips/spinlock.h 2006-12-28 17:18:32.142775000 -0800
@@ -18,6 +18,7 @@
#define __raw_spin_is_locked(x) ((x)->lock != 0)
#define __raw_spin_lock_flags(lock, flags) __raw_spin_lock(lock)
+#define __raw_spin_lock_irq(lock) __raw_spin_lock(lock)
#define __raw_spin_unlock_wait(x) \
do { cpu_relax(); } while ((x)->lock)
Index: linux-2.6.20-rc1/include/asm-parisc/spinlock.h
===================================================================
--- linux-2.6.20-rc1.orig/include/asm-parisc/spinlock.h 2006-11-29 13:57:37.000000000 -0800
+++ linux-2.6.20-rc1/include/asm-parisc/spinlock.h 2006-12-28 17:18:32.142775000 -0800
@@ -12,6 +12,7 @@ static inline int __raw_spin_is_locked(r
}
#define __raw_spin_lock(lock) __raw_spin_lock_flags(lock, 0)
+#define __raw_spin_lock_irq(lock) __raw_spin_lock(lock)
#define __raw_spin_unlock_wait(x) \
do { cpu_relax(); } while (__raw_spin_is_locked(x))
Index: linux-2.6.20-rc1/include/asm-powerpc/spinlock.h
===================================================================
--- linux-2.6.20-rc1.orig/include/asm-powerpc/spinlock.h 2006-11-29 13:57:37.000000000 -0800
+++ linux-2.6.20-rc1/include/asm-powerpc/spinlock.h 2006-12-28 17:18:32.142775000 -0800
@@ -138,6 +138,8 @@ static void __inline__ __raw_spin_lock_f
}
}
+#define __raw_spin_lock_irq(lock) __raw_spin_lock(lock)
+
static __inline__ void __raw_spin_unlock(raw_spinlock_t *lock)
{
SYNC_IO;
Index: linux-2.6.20-rc1/include/asm-ppc/spinlock.h
===================================================================
--- linux-2.6.20-rc1.orig/include/asm-ppc/spinlock.h 2006-11-29 13:57:37.000000000 -0800
+++ linux-2.6.20-rc1/include/asm-ppc/spinlock.h 2006-12-28 17:18:32.142775000 -0800
@@ -13,6 +13,7 @@
#define __raw_spin_unlock_wait(lock) \
do { while (__raw_spin_is_locked(lock)) cpu_relax(); } while (0)
#define __raw_spin_lock_flags(lock, flags) __raw_spin_lock(lock)
+#define __raw_spin_lock_irq(lock) __raw_spin_lock(lock)
static inline void __raw_spin_lock(raw_spinlock_t *lock)
{
Index: linux-2.6.20-rc1/include/asm-s390/spinlock.h
===================================================================
--- linux-2.6.20-rc1.orig/include/asm-s390/spinlock.h 2006-11-29 13:57:37.000000000 -0800
+++ linux-2.6.20-rc1/include/asm-s390/spinlock.h 2006-12-28 17:18:32.142775000 -0800
@@ -54,6 +54,7 @@ _raw_compare_and_swap(volatile unsigned
#define __raw_spin_is_locked(x) ((x)->owner_cpu != 0)
#define __raw_spin_lock_flags(lock, flags) __raw_spin_lock(lock)
+#define __raw_spin_lock_irq(lock) __raw_spin_lock(lock)
#define __raw_spin_unlock_wait(lock) \
do { while (__raw_spin_is_locked(lock)) \
_raw_spin_relax(lock); } while (0)
Index: linux-2.6.20-rc1/include/asm-sh/spinlock.h
===================================================================
--- linux-2.6.20-rc1.orig/include/asm-sh/spinlock.h 2006-11-29 13:57:37.000000000 -0800
+++ linux-2.6.20-rc1/include/asm-sh/spinlock.h 2006-12-28 17:18:32.142775000 -0800
@@ -18,6 +18,7 @@
#define __raw_spin_is_locked(x) ((x)->lock != 0)
#define __raw_spin_lock_flags(lock, flags) __raw_spin_lock(lock)
+#define __raw_spin_lock_irq(lock) __raw_spin_lock(lock)
#define __raw_spin_unlock_wait(x) \
do { cpu_relax(); } while (__raw_spin_is_locked(x))
Index: linux-2.6.20-rc1/include/asm-sparc/spinlock.h
===================================================================
--- linux-2.6.20-rc1.orig/include/asm-sparc/spinlock.h 2006-11-29 13:57:37.000000000 -0800
+++ linux-2.6.20-rc1/include/asm-sparc/spinlock.h 2006-12-28 17:19:24.432775000 -0800
@@ -179,6 +179,7 @@ static inline int __read_trylock(raw_rwl
#define __raw_write_unlock(rw) do { (rw)->lock = 0; } while(0)
#define __raw_spin_lock_flags(lock, flags) __raw_spin_lock(lock)
+#define __raw_spin_lock_irq(lock) __raw_spin_lock(lock)
#define _raw_spin_relax(lock) cpu_relax()
#define _raw_read_relax(lock) cpu_relax()
Index: linux-2.6.20-rc1/include/asm-sparc64/spinlock.h
===================================================================
--- linux-2.6.20-rc1.orig/include/asm-sparc64/spinlock.h 2006-11-29 13:57:37.000000000 -0800
+++ linux-2.6.20-rc1/include/asm-sparc64/spinlock.h 2006-12-28 17:18:32.142775000 -0800
@@ -103,6 +103,8 @@ static inline void __raw_spin_lock_flags
: "memory");
}
+#define __raw_spin_lock_irq(lock) __raw_spin_lock(lock)
+
/* Multi-reader locks, these are much saner than the 32-bit Sparc ones... */
static void inline __read_lock(raw_rwlock_t *lock)
Index: linux-2.6.20-rc1/include/asm-x86_64/spinlock.h
===================================================================
--- linux-2.6.20-rc1.orig/include/asm-x86_64/spinlock.h 2006-12-21 14:34:36.071607104 -0800
+++ linux-2.6.20-rc1/include/asm-x86_64/spinlock.h 2006-12-29 14:17:37.962954000 -0800
@@ -63,6 +63,7 @@ static inline void __raw_spin_lock_flags
"5:\n\t"
: "+m" (lock->slock) : "r" ((unsigned)flags) : "memory");
}
+#define __raw_spin_lock_irq(lock) __raw_spin_lock(lock)
#endif
static inline int __raw_spin_trylock(raw_spinlock_t *lock)
Index: linux-2.6.20-rc1/include/linux/spinlock.h
===================================================================
--- linux-2.6.20-rc1.orig/include/linux/spinlock.h 2006-12-21 14:34:37.241624753 -0800
+++ linux-2.6.20-rc1/include/linux/spinlock.h 2006-12-29 13:54:11.142954000 -0800
@@ -138,6 +138,7 @@ do { \
#ifdef CONFIG_DEBUG_SPINLOCK
extern void _raw_spin_lock(spinlock_t *lock);
#define _raw_spin_lock_flags(lock, flags) _raw_spin_lock(lock)
+#define _raw_spin_lock_irq(lock) _raw_spin_lock(lock)
extern int _raw_spin_trylock(spinlock_t *lock);
extern void _raw_spin_unlock(spinlock_t *lock);
extern void _raw_read_lock(rwlock_t *lock);
@@ -148,6 +149,7 @@ do { \
extern void _raw_write_unlock(rwlock_t *lock);
#else
# define _raw_spin_lock(lock) __raw_spin_lock(&(lock)->raw_lock)
+# define _raw_spin_lock_irq(lock) __raw_spin_lock_irq(&(lock)->raw_lock)
# define _raw_spin_lock_flags(lock, flags) \
__raw_spin_lock_flags(&(lock)->raw_lock, *(flags))
# define _raw_spin_trylock(lock) __raw_spin_trylock(&(lock)->raw_lock)
Index: linux-2.6.20-rc1/kernel/spinlock.c
===================================================================
--- linux-2.6.20-rc1.orig/kernel/spinlock.c 2006-11-29 13:57:37.000000000 -0800
+++ linux-2.6.20-rc1/kernel/spinlock.c 2006-12-28 17:18:32.142775000 -0800
@@ -102,7 +102,11 @@ void __lockfunc _spin_lock_irq(spinlock_
local_irq_disable();
preempt_disable();
spin_acquire(&lock->dep_map, 0, 0, _RET_IP_);
- _raw_spin_lock(lock);
+#ifdef CONFIG_PROVE_LOCKING
+ _raw_spin_lock(lock);
+#else
+ _raw_spin_lock_irq(lock);
+#endif
}
EXPORT_SYMBOL(_spin_lock_irq);
Implement interrupt enabling while spinning for lock for spin_lock_irq
Signed-off by: Pravin B. Shelar <[email protected]>
Signed-off by: Ravikiran Thirumalai <[email protected]>
Signed-off by: Shai Fultheim <[email protected]>
Index: linux-2.6.20-rc1/include/asm-x86_64/spinlock.h
===================================================================
--- linux-2.6.20-rc1.orig/include/asm-x86_64/spinlock.h 2006-12-28 17:18:32.142775000 -0800
+++ linux-2.6.20-rc1/include/asm-x86_64/spinlock.h 2006-12-29 14:05:04.012954000 -0800
@@ -63,7 +63,21 @@ static inline void __raw_spin_lock_flags
"5:\n\t"
: "+m" (lock->slock) : "r" ((unsigned)flags) : "memory");
}
-#define __raw_spin_lock_irq(lock) __raw_spin_lock(lock)
+static inline void __raw_spin_lock_irq(raw_spinlock_t *lock)
+{
+ asm volatile(
+ "\n1:\t"
+ LOCK_PREFIX " ; decl %0\n\t"
+ "jns 2f\n"
+ "sti\n" /* Enable interrupts during spin */
+ "3:\n"
+ "rep;nop\n\t"
+ "cmpl $0,%0\n\t"
+ "jle 3b\n\t"
+ "cli\n"
+ "jmp 1b\n"
+ "2:\t" : "+m" (lock->slock) : : "memory");
+}
#endif
static inline int __raw_spin_trylock(raw_spinlock_t *lock)
On Tue, 2 Jan 2007 23:59:23 -0800
Ravikiran G Thirumalai <[email protected]> wrote:
> The following patches do just that. The first patch is preparatory in nature
> and the second one changes the x86_64 implementation of spin_lock_irq.
> Patch passed overnight runs of kernbench and dbench on 4 way x86_64 smp.
The end result of this is, I think, that i386 enables irqs while spinning
in spin_lock_irqsave() but not while spinning in spin_lock_irq(). And
x86_64 does the opposite.
Odd, isn't it?
On Wed, Jan 03, 2007 at 12:16:35AM -0800, Andrew Morton wrote:
> On Tue, 2 Jan 2007 23:59:23 -0800
> Ravikiran G Thirumalai <[email protected]> wrote:
>
> > The following patches do just that. The first patch is preparatory in nature
> > and the second one changes the x86_64 implementation of spin_lock_irq.
> > Patch passed overnight runs of kernbench and dbench on 4 way x86_64 smp.
>
> The end result of this is, I think, that i386 enables irqs while spinning
> in spin_lock_irqsave() but not while spinning in spin_lock_irq(). And
> x86_64 does the opposite.
No, right now we have on mainline (non PREEMPT case);
i386 x86_64
-----------------------------------------------------------------------------
spin_lock_irq cli when spin cli when spin
spin_lock_irqsave spin with intr enabled spin with intr enabled
The posted patchset changed this to:
i386 x86_64
-----------------------------------------------------------------------------
spin_lock_irq cli when spin spin with intr enabled
spin_lock_irqsave spin with intr enabled spin with intr enabled
>
> Odd, isn't it?
Well we just implemented the x86_64 part. Here goes the i386 part as well for
spin_lock_irq.
i386: Enable interrupts while spinning for a lock with spin_lock_irq
Signed-off-by: Ravikiran Thirumalai <[email protected]>
Index: linux-2.6.20-rc1/include/asm-i386/spinlock.h
===================================================================
--- linux-2.6.20-rc1.orig/include/asm-i386/spinlock.h 2006-12-28 17:18:32.142775000 -0800
+++ linux-2.6.20-rc1/include/asm-i386/spinlock.h 2007-01-03 10:18:32.243662000 -0800
@@ -82,7 +82,22 @@ static inline void __raw_spin_lock_flags
CLI_STI_INPUT_ARGS
: "memory" CLI_STI_CLOBBERS);
}
-# define __raw_spin_lock_irq(lock) __raw_spin_lock(lock)
+
+static inline void __raw_spin_lock_irq(raw_spinlock_t *lock)
+{
+ asm volatile("\n1:\t"
+ LOCK_PREFIX " ; decb %0\n\t"
+ "jns 3f\n"
+ STI_STRING "\n"
+ "2:\t"
+ "rep;nop\n\t"
+ "cmpb $0,%0\n\t"
+ "jle 2b\n\t"
+ CLI_STRING "\n"
+ "jmp 1b\n"
+ "3:\n\t"
+ : "+m" (lock->slock) : : "memory");
+}
#endif
static inline int __raw_spin_trylock(raw_spinlock_t *lock)