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SubjectRe: 2.5.57 IO slowdown with CONFIG_PREEMPT enabled
Robert Macaulay <robert_macaulay@dell.com> wrote:
>
> No change either

OK, thanks. The below patch reverts the spinlocking change,
if you could please test that with CONFIG_PREEMPT=y

>
> I have been hitting an odd issue, and I haven't had a chance to traceback
> to where it came from(versionwise). FS changes seem to be getting rolled
> back at times. For example, I run make menuconfig, add my config options
> for CONFIG_MEGARAID to be built in, and recompile kernel. I install and
> reboot, and that config file, which contained CONFIG_MEGARAID=y, reverts
> back to its original state. multiple syncs seem to keep this in the
> correct state. The filesystem that this is occuring on is ext3, mounted
> with defaults, on a megaraid controller. I'll trace this down later and
> post results.

Suggest that you make sure it's not some strangeness in the kernel build
system which is writing out a modified .config file.



include/linux/spinlock.h | 56 ++++++++++++++---------------------------------
kernel/ksyms.c | 4 ---
kernel/sched.c | 47 ---------------------------------------
3 files changed, 17 insertions(+), 90 deletions(-)

diff -puN include/linux/spinlock.h~preempt-oddity include/linux/spinlock.h
--- 25/include/linux/spinlock.h~preempt-oddity Wed Jan 15 14:28:20 2003
+++ 25-akpm/include/linux/spinlock.h Wed Jan 15 14:28:53 2003
@@ -85,37 +85,31 @@
* regardless of whether CONFIG_SMP or CONFIG_PREEMPT are set. The various
* methods are defined as nops in the case they are not required.
*/
-#define spin_trylock(lock) ({preempt_disable(); _raw_spin_trylock(lock) ? \
- 1 : ({preempt_enable(); 0;});})
+#define spin_lock(lock) \
+do { \
+ preempt_disable(); \
+ _raw_spin_lock(lock); \
+} while(0)

-#define write_trylock(lock) ({preempt_disable();_raw_write_trylock(lock) ? \
+#define spin_trylock(lock) ({preempt_disable(); _raw_spin_trylock(lock) ? \
1 : ({preempt_enable(); 0;});})

-/* Where's read_trylock? */
-
-#if defined(CONFIG_SMP) && defined(CONFIG_PREEMPT)
-void __preempt_spin_lock(spinlock_t *lock);
-void __preempt_write_lock(rwlock_t *lock);
-
-#define spin_lock(lock) \
+#define spin_unlock(lock) \
do { \
- preempt_disable(); \
- if (unlikely(!_raw_spin_trylock(lock))) \
- __preempt_spin_lock(lock); \
+ _raw_spin_unlock(lock); \
+ preempt_enable(); \
} while (0)

-#define write_lock(lock) \
+#define read_lock(lock) \
do { \
preempt_disable(); \
- if (unlikely(!_raw_write_trylock(lock))) \
- __preempt_write_lock(lock); \
-} while (0)
+ _raw_read_lock(lock); \
+} while(0)

-#else
-#define spin_lock(lock) \
+#define read_unlock(lock) \
do { \
- preempt_disable(); \
- _raw_spin_lock(lock); \
+ _raw_read_unlock(lock); \
+ preempt_enable(); \
} while(0)

#define write_lock(lock) \
@@ -123,19 +117,6 @@ do { \
preempt_disable(); \
_raw_write_lock(lock); \
} while(0)
-#endif
-
-#define read_lock(lock) \
-do { \
- preempt_disable(); \
- _raw_read_lock(lock); \
-} while(0)
-
-#define spin_unlock(lock) \
-do { \
- _raw_spin_unlock(lock); \
- preempt_enable(); \
-} while (0)

#define write_unlock(lock) \
do { \
@@ -143,11 +124,8 @@ do { \
preempt_enable(); \
} while(0)

-#define read_unlock(lock) \
-do { \
- _raw_read_unlock(lock); \
- preempt_enable(); \
-} while(0)
+#define write_trylock(lock) ({preempt_disable();_raw_write_trylock(lock) ? \
+ 1 : ({preempt_enable(); 0;});})

#define spin_lock_irqsave(lock, flags) \
do { \
diff -puN kernel/sched.c~preempt-oddity kernel/sched.c
--- 25/kernel/sched.c~preempt-oddity Wed Jan 15 14:28:24 2003
+++ 25-akpm/kernel/sched.c Wed Jan 15 14:28:53 2003
@@ -2278,50 +2278,3 @@ void __might_sleep(char *file, int line)
#endif
}
#endif
-
-
-#if defined(CONFIG_SMP) && defined(CONFIG_PREEMPT)
-/*
- * This could be a long-held lock. If another CPU holds it for a long time,
- * and that CPU is not asked to reschedule then *this* CPU will spin on the
- * lock for a long time, even if *this* CPU is asked to reschedule.
- *
- * So what we do here, in the slow (contended) path is to spin on the lock by
- * hand while permitting preemption.
- *
- * Called inside preempt_disable().
- */
-void __preempt_spin_lock(spinlock_t *lock)
-{
- if (preempt_count() > 1) {
- _raw_spin_lock(lock);
- return;
- }
-
- while (!_raw_spin_trylock(lock)) {
- if (need_resched()) {
- preempt_enable_no_resched();
- __cond_resched();
- preempt_disable();
- }
- cpu_relax();
- }
-}
-
-void __preempt_write_lock(rwlock_t *lock)
-{
- if (preempt_count() > 1) {
- _raw_write_lock(lock);
- return;
- }
-
- while (!_raw_write_trylock(lock)) {
- if (need_resched()) {
- preempt_enable_no_resched();
- __cond_resched();
- preempt_disable();
- }
- cpu_relax();
- }
-}
-#endif
diff -puN kernel/ksyms.c~preempt-oddity kernel/ksyms.c
--- 25/kernel/ksyms.c~preempt-oddity Wed Jan 15 14:28:30 2003
+++ 25-akpm/kernel/ksyms.c Wed Jan 15 14:28:53 2003
@@ -493,10 +493,6 @@ EXPORT_SYMBOL(do_settimeofday);
#ifdef CONFIG_DEBUG_SPINLOCK_SLEEP
EXPORT_SYMBOL(__might_sleep);
#endif
-#if defined(CONFIG_SMP) && defined(CONFIG_PREEMPT)
-EXPORT_SYMBOL(__preempt_spin_lock);
-EXPORT_SYMBOL(__preempt_write_lock);
-#endif
#if !defined(__ia64__)
EXPORT_SYMBOL(loops_per_jiffy);
#endif
_

-
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