[RFC: 2.6 patch] remove the CONFIG_CC_ALIGN_* options

[RFC: 2.6 patch] remove the CONFIG_CC_ALIGN_* options

[Adrian Bunk]

I don't see any use case for the CONFIG_CC_ALIGN_* options:
- they are only available if EMBEDDED
- people using EMBEDDED will most likely also enable 
  CC_OPTIMIZE_FOR_SIZE
- the default for -Os is to disable alignment


Signed-off-by: Adrian Bunk <bunk@stusta.de>

---

 Makefile     |    7 -------
 init/Kconfig |   37 -------------------------------------
 2 files changed, 44 deletions(-)

--- linux-2.6.16-rc2-mm1-full/init/Kconfig.old	2006-02-12 15:30:08.000000000 +0100
+++ linux-2.6.16-rc2-mm1-full/init/Kconfig	2006-02-12 15:30:53.000000000 +0100
@@ -353,45 +353,8 @@
 	  to userspace as tmpfs if TMPFS is enabled. Disabling this
 	  option replaces shmem and tmpfs with the much simpler ramfs code,
 	  which may be appropriate on small systems without swap.
 
-config CC_ALIGN_FUNCTIONS
-	int "Function alignment" if EMBEDDED
-	default 0
-	help
-	  Align the start of functions to the next power-of-two greater than n,
-	  skipping up to n bytes.  For instance, 32 aligns functions
-	  to the next 32-byte boundary, but 24 would align to the next
-	  32-byte boundary only if this can be done by skipping 23 bytes or less.
-	  Zero means use compiler's default.
-
-config CC_ALIGN_LABELS
-	int "Label alignment" if EMBEDDED
-	default 0
-	help
-	  Align all branch targets to a power-of-two boundary, skipping
-	  up to n bytes like ALIGN_FUNCTIONS.  This option can easily
-	  make code slower, because it must insert dummy operations for
-	  when the branch target is reached in the usual flow of the code.
-	  Zero means use compiler's default.
-
-config CC_ALIGN_LOOPS
-	int "Loop alignment" if EMBEDDED
-	default 0
-	help
-	  Align loops to a power-of-two boundary, skipping up to n bytes.
-	  Zero means use compiler's default.
-
-config CC_ALIGN_JUMPS
-	int "Jump alignment" if EMBEDDED
-	default 0
-	help
-	  Align branch targets to a power-of-two boundary, for branch
-	  targets where the targets can only be reached by jumping,
-	  skipping up to n bytes like ALIGN_FUNCTIONS.  In this case,
-	  no dummy operations need be executed.
-	  Zero means use compiler's default.
-
 config SLAB
 	default y
 	bool "Use full SLAB allocator" if EMBEDDED
 	help
--- linux-2.6.16-rc2-mm1-full/Makefile.old	2006-02-12 15:30:59.000000000 +0100
+++ linux-2.6.16-rc2-mm1-full/Makefile	2006-02-12 15:31:24.000000000 +0100
@@ -473,15 +473,8 @@
 else
 CFLAGS		+= -O2
 endif
 
-#Add align options if CONFIG_CC_* is not equal to 0
-add-align = $(if $(filter-out 0,$($(1))),$(cc-option-align)$(2)=$($(1)))
-CFLAGS		+= $(call add-align,CONFIG_CC_ALIGN_FUNCTIONS,-functions)
-CFLAGS		+= $(call add-align,CONFIG_CC_ALIGN_LABELS,-labels)
-CFLAGS		+= $(call add-align,CONFIG_CC_ALIGN_LOOPS,-loops)
-CFLAGS		+= $(call add-align,CONFIG_CC_ALIGN_JUMPS,-jumps)
-
 ifdef CONFIG_FRAME_POINTER
 CFLAGS		+= -fno-omit-frame-pointer $(call cc-option,-fno-optimize-sibling-calls,)
 else
 CFLAGS		+= -fomit-frame-pointer

Re: [RFC: 2.6 patch] remove the CONFIG_CC_ALIGN_* options

[Benjamin LaHaise]

On Sun, Feb 12, 2006 at 06:48:02PM +0100, Adrian Bunk wrote:
> I don't see any use case for the CONFIG_CC_ALIGN_* options:
> - they are only available if EMBEDDED
> - people using EMBEDDED will most likely also enable 
>   CC_OPTIMIZE_FOR_SIZE
> - the default for -Os is to disable alignment

CONFIG_EMBEDDED should actually be spell CONFIG_ADVANCED.  Not everyone 
testing different alignments is building an embedded system targetted for 
size.  The option is just as useful in doing performance comparisons.  
Besides, is it really a maintenence load?

		-ben

Re: [RFC: 2.6 patch] remove the CONFIG_CC_ALIGN_* options

[Adrian Bunk]

On Sun, Feb 12, 2006 at 04:40:46PM -0500, Benjamin LaHaise wrote:
> On Sun, Feb 12, 2006 at 06:48:02PM +0100, Adrian Bunk wrote:
> > I don't see any use case for the CONFIG_CC_ALIGN_* options:
> > - they are only available if EMBEDDED
> > - people using EMBEDDED will most likely also enable 
> >   CC_OPTIMIZE_FOR_SIZE
> > - the default for -Os is to disable alignment
> 
> CONFIG_EMBEDDED should actually be spell CONFIG_ADVANCED.  Not everyone 

We need both with CONFIG_EMBEDDED depending on CONFIG_ADVANCED (see my 
other email).

> testing different alignments is building an embedded system targetted for 
> size.  The option is just as useful in doing performance comparisons.  
> Besides, is it really a maintenence load?

It is not a maintenence load, but does it make sense to offer this in 
any way to _users_?

gcc already sets this options with -Os/-O2.

We do already override the choice of gcc in some cpu specific cases.

If someone is doing performance comparisons and discovers that the 
default settings gcc chooses aren't good, the only sane thing is to 
discuss whether it makes sense to change this.

> 		-ben

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed