* Linus Torvalds <[email protected]> wrote:
> Umm. i386 spinlocks could and should be *one*byte*.
>
> In fact, I don't even know why they are wasting four bytes right now:
> the fact that somebody made them an "int" just wastes memory. All the
> actual code uses "decb", so it's not even a question of safety. I
> wonder why we have that 32-bit thing and the ugly casts.
>
> Ingo, any memory of that?
no real reason that i can recall - i guess nobody dared to touch it
because it used to have that 'volatile', indicating black voodoo ;-) Now
that the bad stigma has been removed, we could try the patch below. It
boots fine here, and we save 1K of kernel text size:
text data bss dec hex filename
6236003 611992 401408 7249403 6e9dfb vmlinux.before
6235075 611992 401408 7248475 6e9a5b vmlinux.after
I can understand why no data is saved by this change: gcc is aligning
the next field to a natural boundary anyway and we dont really have
arrays of spinlocks (fortunately). [and we save no data even if using
the ((packed)) attribute.] Perhaps some data structure that is never in
the kernel image itself still got smaller? Any good way to determine
that?
But why is the text size different? Ah: i think it's spin_lock_init()
getting shorter :-)
but this is certainly not something for 2.6.22, it's an early 2.6.23
matter i suspect.
Ingo
------------------->
From: Ingo Molnar <[email protected]>
Subject: [patch] spinlocks i386: change them to byte fields
all spinlock ops are on byte operands, so change the spinlock field to
be unsigned char. This saves a bit of kernel text size:
text data bss dec hex filename
6236003 611992 401408 7249403 6e9dfb vmlinux.before
6235075 611992 401408 7248475 6e9a5b vmlinux.after
Signed-off-by: Ingo Molnar <[email protected]>
---
include/asm-i386/spinlock_types.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
Index: linux/include/asm-i386/spinlock_types.h
===================================================================
--- linux.orig/include/asm-i386/spinlock_types.h
+++ linux/include/asm-i386/spinlock_types.h
@@ -6,7 +6,7 @@
#endif
typedef struct {
- unsigned int slock;
+ unsigned char slock;
} raw_spinlock_t;
#define __RAW_SPIN_LOCK_UNLOCKED { 1 }
-
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