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SubjectRe: [PATCH][2.6] Completely out of line spinlocks / i386
On Sat, 7 Aug 2004, Linus Torvalds wrote:

> On Sun, 8 Aug 2004, Zwane Mwaikambo wrote:
> > >
> > > that looks just broken.
> >
> > _raw_spin_lock will have the symbol __spin_lock_loop{,_flags} when used in
> > symbols, modules won't load otherwise.
>
> Yes, I was talking about the "failed" things only. The non-failure-cases
> obviously do have to be exported.

Thanks, here is a cleaned up version, we seem to have even managed to save
some text (~5k), gcc probably managed to do the asm call setup without too
much register shuffling. I still find the decrease in data odd.

text data bss dec hex filename
5527214 873510 321872 6722596 669424 vmlinux-before
5480308 867964 321872 6670144 65c740 vmlinux-after
5474492 867930 321872 6664294 65b066 vmlinux-after2

arch/i386/Kconfig | 10 ++++++++++
arch/i386/lib/Makefile | 1 +
arch/i386/lib/spinlock.c | 38 ++++++++++++++++++++++++++++++++++++++
include/asm-i386/spinlock.h | 22 ++++++++++++++++++++--
4 files changed, 69 insertions(+), 2 deletions(-)
Index: linux-2.6.8-rc3-mm1/arch/i386/Kconfig
===================================================================
RCS file: /home/cvsroot/linux-2.6.8-rc3-mm1/arch/i386/Kconfig,v
retrieving revision 1.1.1.1
diff -u -p -B -r1.1.1.1 Kconfig
--- linux-2.6.8-rc3-mm1/arch/i386/Kconfig 5 Aug 2004 16:37:39 -0000 1.1.1.1
+++ linux-2.6.8-rc3-mm1/arch/i386/Kconfig 7 Aug 2004 23:07:05 -0000
@@ -1262,6 +1262,16 @@ config DEBUG_SPINLOCK
best used in conjunction with the NMI watchdog so that spinlock
deadlocks are also debuggable.

+config COOL_SPINLOCK
+ bool "Completely out of line spinlocks"
+ depends on SMP
+ default y
+ help
+ Say Y here to build spinlocks which have common text for contended
+ and uncontended paths. This reduces kernel text size by at least
+ 50k on most configurations, plus there is the additional benefit
+ of better cache utilisation.
+
config DEBUG_PAGEALLOC
bool "Page alloc debugging"
depends on DEBUG_KERNEL
Index: linux-2.6.8-rc3-mm1/arch/i386/lib/Makefile
===================================================================
RCS file: /home/cvsroot/linux-2.6.8-rc3-mm1/arch/i386/lib/Makefile,v
retrieving revision 1.1.1.1
diff -u -p -B -r1.1.1.1 Makefile
--- linux-2.6.8-rc3-mm1/arch/i386/lib/Makefile 5 Aug 2004 16:37:39 -0000 1.1.1.1
+++ linux-2.6.8-rc3-mm1/arch/i386/lib/Makefile 7 Aug 2004 22:51:37 -0000
@@ -6,6 +6,7 @@
lib-y = checksum.o delay.o usercopy.o getuser.o memcpy.o strstr.o \
bitops.o

+lib-$(CONFIG_COOL_SPINLOCK) += spinlock.o
lib-$(CONFIG_X86_USE_3DNOW) += mmx.o
lib-$(CONFIG_HAVE_DEC_LOCK) += dec_and_lock.o
lib-$(CONFIG_KGDB) += kgdb_serial.o
Index: linux-2.6.8-rc3-mm1/arch/i386/lib/spinlock.c
===================================================================
RCS file: linux-2.6.8-rc3-mm1/arch/i386/lib/spinlock.c
diff -N linux-2.6.8-rc3-mm1/arch/i386/lib/spinlock.c
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ linux-2.6.8-rc3-mm1/arch/i386/lib/spinlock.c 8 Aug 2004 05:39:13 -0000
@@ -0,0 +1,38 @@
+#include <linux/module.h>
+
+#define PROC(name) \
+ ".align 4\n" \
+ ".globl " #name"\n" \
+ #name":\n"
+
+asm (PROC(__spin_lock_loop_flags)
+ "lock; decb (%eax)\n\t"
+ "js 1f\n\t"
+ "nop\n\t"
+ "ret\n\t"
+ "1:\n\t"
+ "testl $0x200, %edx\n\t"
+ "jz 1f\n\t"
+ "sti\n\t"
+ "2: rep; nop\n\t"
+ "cmpb $0, (%eax)\n\t"
+ "jle 2b\n\t"
+ "cli\n\t"
+ "jmp __spin_lock_loop_flags\n\t"
+);
+
+asm (PROC(__spin_lock_loop)
+ "lock; decb (%eax)\n\t"
+ "js 1f\n\t"
+ "nop\n\t"
+ "ret\n\t"
+ "1: rep; nop\n\t"
+ "cmpb $0, (%eax)\n\t"
+ "jle 1b\n\t"
+ "jmp __spin_lock_loop\n\t"
+);
+
+void __spin_lock_loop_flags(void);
+void __spin_lock_loop(void);
+EXPORT_SYMBOL(__spin_lock_loop_flags);
+EXPORT_SYMBOL(__spin_lock_loop);
Index: linux-2.6.8-rc3-mm1/include/asm-i386/spinlock.h
===================================================================
RCS file: /home/cvsroot/linux-2.6.8-rc3-mm1/include/asm-i386/spinlock.h,v
retrieving revision 1.1.1.1
diff -u -p -B -r1.1.1.1 spinlock.h
--- linux-2.6.8-rc3-mm1/include/asm-i386/spinlock.h 5 Aug 2004 16:37:51 -0000 1.1.1.1
+++ linux-2.6.8-rc3-mm1/include/asm-i386/spinlock.h 8 Aug 2004 05:19:10 -0000
@@ -43,6 +43,13 @@ typedef struct {
#define spin_is_locked(x) (*(volatile signed char *)(&(x)->lock) <= 0)
#define spin_unlock_wait(x) do { barrier(); } while(spin_is_locked(x))

+#ifdef CONFIG_COOL_SPINLOCK
+ #define spin_lock_string \
+ "call __spin_lock_loop\n\t"
+
+ #define spin_lock_string_flags \
+ "call __spin_lock_loop_flags\n\t"
+#else
#define spin_lock_string \
"\n1:\t" \
"lock ; decb %0\n\t" \
@@ -71,6 +78,7 @@ typedef struct {
"cli\n\t" \
"jmp 1b\n" \
LOCK_SECTION_END
+#endif

/*
* This works. Despite all the confusion.
@@ -139,7 +147,12 @@ here:
#endif
__asm__ __volatile__(
spin_lock_string
- :"=m" (lock->lock) : : "memory");
+#ifdef CONFIG_COOL_SPINLOCK
+ : : "a" (&lock->lock) : "memory"
+#else
+ :"=m" (lock->lock) : : "memory"
+#endif
+ );
}

static inline void _raw_spin_lock_flags (spinlock_t *lock, unsigned long flags)
@@ -154,7 +167,12 @@ here:
#endif
__asm__ __volatile__(
spin_lock_string_flags
- :"=m" (lock->lock) : "r" (flags) : "memory");
+#ifdef CONFIG_COOL_SPINLOCK
+ : : "a" (&lock->lock), "d" (flags) : "memory"
+#else
+ :"=m" (lock->lock) : "r" (flags) : "memory"
+#endif
+ );
}

/*
-
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