[patch] spinlocks: remove 'volatile'

[Ingo Molnar]

* Linus Torvalds <torvalds@xxxxxxxx> 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@xxxxxxx>

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@xxxxxxx>
---
 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 }
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/