[PATCH] reduce code in generic spinlock.h

[PATCH] reduce code in generic spinlock.h

[Dave Hansen]

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The last time lockmeter was ported to 2.5, it was getting a little
messy.  There were separate declarations for spin_*lock() for each
combination of lockmeter and preemption, which made four, plus the
no-smp definition.  While lockmeter's mess isn't the kernel's fault, 
we noticed some some simplifications which could be made to the 
generic spinlock code.  This patch uses a single definition for each 
of the macros, eliminating some redundant code.

In the preemption-off case, spin lock is changed from this:
_raw_spin_lock(lock)
to this:
do {
	preempt_disable();
	_raw_spin_lock(lock)
} while (0)
The preemption-on case is unchanged.

Since preempt_disable() is a do{}while(0) with preemption off anyway,
it gets back to the same effective result as before, with a little
extra work from the compiler.  The preempt_disable() macro just had to
be moved up in the file a bit.

Thanks to Adam Litke <aglitke@us.ibm.com>, who has been doing the
lockmeter port and who initially wrote this patch.

Compiles in all combinations of SMP and preempt.
-- 
Dave Hansen
haveblue@us.ibm.com



[-- Attachment #2: spinlock-cleanup-2.5.27-2.diff --]
[-- Type: text/plain, Size: 1691 bytes --]

diff -ur linux-2.5.27-clean/include/linux/spinlock.h linux-2.5.27/include/linux/spinlock.h
--- linux-2.5.27-clean/include/linux/spinlock.h	Tue Jul 23 09:19:51 2002
+++ linux-2.5.27/include/linux/spinlock.h	Tue Jul 23 09:26:16 2002
@@ -150,6 +150,14 @@
 		preempt_schedule(); \
 } while (0)
 
+#else /* !CONFIG_PREEMPT */
+#define preempt_get_count()		(0)
+#define preempt_disable()		do { } while(0)
+#define preempt_enable_no_resched()	do { } while(0)
+#define preempt_enable()		do { } while(0)
+#define preempt_check_resched()		do { } while(0)
+#endif /* !CONFIG_PREEMPT */
+
 #define spin_lock(lock)	\
 do { \
 	preempt_disable(); \
@@ -176,26 +184,6 @@
 #define write_unlock(lock)	({_raw_write_unlock(lock); preempt_enable();})
 #define write_trylock(lock)	({preempt_disable();_raw_write_trylock(lock) ? \
 				1 : ({preempt_enable(); 0;});})
-
-#else
-
-#define preempt_get_count()		(0)
-#define preempt_disable()		do { } while (0)
-#define preempt_enable_no_resched()	do {} while(0)
-#define preempt_enable()		do { } while (0)
-#define preempt_check_resched()		do { } while (0)
-
-#define spin_lock(lock)			_raw_spin_lock(lock)
-#define spin_trylock(lock)		_raw_spin_trylock(lock)
-#define spin_unlock(lock)		_raw_spin_unlock(lock)
-#define spin_unlock_no_resched(lock)	_raw_spin_unlock(lock)
-
-#define read_lock(lock)			_raw_read_lock(lock)
-#define read_unlock(lock)		_raw_read_unlock(lock)
-#define write_lock(lock)		_raw_write_lock(lock)
-#define write_unlock(lock)		_raw_write_unlock(lock)
-#define write_trylock(lock)		_raw_write_trylock(lock)
-#endif
 
 /* "lock on reference count zero" */
 #ifndef ATOMIC_DEC_AND_LOCK
Only in linux-2.5.27-clean/include/linux: spinlock.h.orig

Re: [PATCH] reduce code in generic spinlock.h

[Robert Love]

On Tue, 2002-07-23 at 09:28, Dave Hansen wrote:

> The last time lockmeter was ported to 2.5, it was getting a little
> messy.  There were separate declarations for spin_*lock() for each
> combination of lockmeter and preemption, which made four, plus the
> no-smp definition.  While lockmeter's mess isn't the kernel's fault, 
> we noticed some some simplifications which could be made to the 
> generic spinlock code.  This patch uses a single definition for each 
> of the macros, eliminating some redundant code.

I have no problems with this (assuming it is right and it looks so on
first glance).

It will not apply to Linus's current tree, however, because of the IRQ
rewrite that is now applied.  If you pull his BK tree and diff against
that, you should be OK... most notably, the preemption code has moved to
preempt.h.

	Robert Love

Re: [PATCH] reduce code in generic spinlock.h

[Dave Hansen]

Robert Love wrote:
> On Tue, 2002-07-23 at 09:28, Dave Hansen wrote:
> 
>>The last time lockmeter was ported to 2.5, it was getting a little
>>messy.  There were separate declarations for spin_*lock() for each
>>combination of lockmeter and preemption, which made four, plus the
>>no-smp definition.  While lockmeter's mess isn't the kernel's fault, 
>>we noticed some some simplifications which could be made to the 
>>generic spinlock code.  This patch uses a single definition for each 
>>of the macros, eliminating some redundant code.
> 
> I have no problems with this (assuming it is right and it looks so on
> first glance).
> 
> It will not apply to Linus's current tree, however, because of the IRQ
> rewrite that is now applied.  If you pull his BK tree and diff against
> that, you should be OK... most notably, the preemption code has moved to
> preempt.h.

D'oh.  Bad timing, I guess.  I'll rediff against current BK.


-- 
Dave Hansen
haveblue@us.ibm.com

Re: [PATCH] reduce code in generic spinlock.h

[Dave Hansen]

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Robert Love wrote:
> It will not apply to Linus's current tree, however, because of the IRQ
> rewrite that is now applied.  If you pull his BK tree and diff against
> that, you should be OK... most notably, the preemption code has moved to
> preempt.h.

OK, this just made it simpler.  Just remove the preempt ifdef and the 
extra spinlock calls.  Patch against latest BK attached.

-- 
Dave Hansen
haveblue@us.ibm.com

[-- Attachment #2: spinlock-cleanup-bk0723.diff --]
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diff -Nru a/include/linux/spinlock.h b/include/linux/spinlock.h
--- a/include/linux/spinlock.h	Tue Jul 23 13:56:42 2002
+++ b/include/linux/spinlock.h	Tue Jul 23 13:56:42 2002
@@ -119,8 +119,6 @@
 
 #endif /* !SMP */
 
-#ifdef CONFIG_PREEMPT
-
 #define spin_lock(lock)	\
 do { \
 	preempt_disable(); \
@@ -147,20 +145,6 @@
 #define write_unlock(lock)	({_raw_write_unlock(lock); preempt_enable();})
 #define write_trylock(lock)	({preempt_disable();_raw_write_trylock(lock) ? \
 				1 : ({preempt_enable(); 0;});})
-
-#else
-
-#define spin_lock(lock)			_raw_spin_lock(lock)
-#define spin_trylock(lock)		_raw_spin_trylock(lock)
-#define spin_unlock(lock)		_raw_spin_unlock(lock)
-#define spin_unlock_no_resched(lock)	_raw_spin_unlock(lock)
-
-#define read_lock(lock)			_raw_read_lock(lock)
-#define read_unlock(lock)		_raw_read_unlock(lock)
-#define write_lock(lock)		_raw_write_lock(lock)
-#define write_unlock(lock)		_raw_write_unlock(lock)
-#define write_trylock(lock)		_raw_write_trylock(lock)
-#endif
 
 /* "lock on reference count zero" */
 #ifndef ATOMIC_DEC_AND_LOCK