[PATCH] reduce code in generic spinlock.h

Dave Hansen
2002-07-23T16:26:05Z

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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

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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