[patch] spinlocks: remove 'volatile'

Ingo Molnar
2006-07-06T08:21:17Z

* Linus Torvalds <torvalds@osdl.org> wrote:

> I wonder if we should remove the "volatile". There really isn't
> anything _good_ that gcc can do with it, but we've seen gcc code
> generation do stupid things before just because "volatile" seems to
> just disable even proper normal working.

yeah. I tried this and it indeed slashed 42K off text size (0.2%):

text data bss dec filename
20779489 6073834 3075176 29928499 vmlinux.volatile
20736884 6073834 3075176 29885894 vmlinux.non-volatile

i booted the resulting allyesconfig bzImage and everything seems to be
working fine. Find patch below.

Ingo

------------------>
Subject: spinlocks: remove 'volatile'
From: Ingo Molnar <mingo@elte.hu>

remove 'volatile' from the spinlock types, it causes gcc to
generate really bad code. (and it's pointless anyway)

this reduces the non-debug SMP kernel's size by 0.2% (!).

Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
include/asm-i386/spinlock_types.h | 4 ++--
include/asm-x86_64/spinlock_types.h | 4 ++--
2 files changed, 4 insertions(+), 4 deletions(-)

Index: linux/include/asm-i386/spinlock_types.h
===================================================================
--- linux.orig/include/asm-i386/spinlock_types.h
+++ linux/include/asm-i386/spinlock_types.h
@@ -6,13 +6,13 @@
#endif

typedef struct {
- volatile unsigned int slock;
+ unsigned int slock;
} raw_spinlock_t;

#define __RAW_SPIN_LOCK_UNLOCKED { 1 }

typedef struct {
- volatile unsigned int lock;
+ unsigned int lock;
} raw_rwlock_t;

#define __RAW_RW_LOCK_UNLOCKED { RW_LOCK_BIAS }
Index: linux/include/asm-x86_64/spinlock_types.h
===================================================================
--- linux.orig/include/asm-x86_64/spinlock_types.h
+++ linux/include/asm-x86_64/spinlock_types.h
@@ -6,13 +6,13 @@
#endif

typedef struct {
- volatile unsigned int slock;
+ unsigned int slock;
} raw_spinlock_t;

#define __RAW_SPIN_LOCK_UNLOCKED { 1 }

typedef struct {
- volatile unsigned int lock;
+ unsigned int lock;
} raw_rwlock_t;

#define __RAW_RW_LOCK_UNLOCKED { RW_LOCK_BIAS }