Value of __*{init,exit} anotations?

Value of __*{init,exit} anotations?

[Adrian Bunk]

On Wed, Jan 30, 2008 at 03:41:35PM -0600, James Bottomley wrote:
> On Wed, 2008-01-30 at 22:20 +0100, Sam Ravnborg wrote:
> > On Wed, Jan 30, 2008 at 03:00:16PM -0600, James Bottomley wrote:
>...
> > > __init is possibly justifiable with a few hundred k savings on boot.
> > > __devinit and the rest are surely killable on the grounds they provide
> > > little benefit for all the pain they cause.
> > For the embedded people a few kb here and there is worth it.
> > 
> > > all __exit seems to do is set us up for unreferenced pointers in
> > > discarded sections, so could we kill that too?
> > Again - savings when we build-in the drivers.
> > And without the checks we see 'funny' linker errors on the architectues
> > that can continue to add the .exit.text in /DISCARD/
> 
> Perhaps you have different figures, but my standard kernel linking ones
> tell me that the discard sections only save tens of k (not hundreds that
> the init ones save), so I really do think they have no real benefit and
> land us huge problems of pointer references into discarded sections.
> 
> I don't deny we can invest large amounts of work to fix our current
> issues and build large scriptable checks to ensure we keep it fixed ...
> I'm just asking if, at the end of the day, it's really worth it.

Some people consider it worth it for their memory restricted systems
and would like to drive the annotations even further. [1]

My experience while fixing section bugs during the last years is that 
the __dev{init,exit}* are actually the main question since they are both 
the majority of annotations and the ones that bring benefits only 
in a case that has become very exotic (CONFIG_HOTPLUG=n).

All the other annotations either both bring value for everyone
(plain __init* and __exit*) or are nothing normal drivers would
use (__cpu* and _mem*).

People at linux-arch (Cc'ed) might be better at explaining how often 
CONFIG_HOTPLUG gets used in real-life systems and how big the savings 
are there.

That might be a good basis for deciding whether it's worth it.

> James

cu
Adrian

[1] http://lkml.org/lkml/2007/10/12/297

-- 

       "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

Re: Value of __*{init,exit} anotations?

[James Bottomley]

On Thu, 2008-01-31 at 00:32 +0200, Adrian Bunk wrote:
> On Wed, Jan 30, 2008 at 03:41:35PM -0600, James Bottomley wrote:
> > On Wed, 2008-01-30 at 22:20 +0100, Sam Ravnborg wrote:
> > > On Wed, Jan 30, 2008 at 03:00:16PM -0600, James Bottomley wrote:
> >...
> > > > __init is possibly justifiable with a few hundred k savings on boot.
> > > > __devinit and the rest are surely killable on the grounds they provide
> > > > little benefit for all the pain they cause.
> > > For the embedded people a few kb here and there is worth it.
> > > 
> > > > all __exit seems to do is set us up for unreferenced pointers in
> > > > discarded sections, so could we kill that too?
> > > Again - savings when we build-in the drivers.
> > > And without the checks we see 'funny' linker errors on the architectues
> > > that can continue to add the .exit.text in /DISCARD/
> > 
> > Perhaps you have different figures, but my standard kernel linking ones
> > tell me that the discard sections only save tens of k (not hundreds that
> > the init ones save), so I really do think they have no real benefit and
> > land us huge problems of pointer references into discarded sections.
> > 
> > I don't deny we can invest large amounts of work to fix our current
> > issues and build large scriptable checks to ensure we keep it fixed ...
> > I'm just asking if, at the end of the day, it's really worth it.
> 
> Some people consider it worth it for their memory restricted systems
> and would like to drive the annotations even further. [1]
> 
> My experience while fixing section bugs during the last years is that 
> the __dev{init,exit}* are actually the main question since they are both 
> the majority of annotations and the ones that bring benefits only 
> in a case that has become very exotic (CONFIG_HOTPLUG=n).
> 
> All the other annotations either both bring value for everyone
> (plain __init* and __exit*) or are nothing normal drivers would
> use (__cpu* and _mem*).
> 
> People at linux-arch (Cc'ed) might be better at explaining how often 
> CONFIG_HOTPLUG gets used in real-life systems and how big the savings 
> are there.
> 
> That might be a good basis for deciding whether it's worth it.

I'll certainly buy this.  Perhaps killing everything other than __init
and __exit (meaning discardable whether the system is hotplug, suspend
or whatever) might get rid of 90% of the problem while still preserving
90% of the benefits.  I think a lot of the issues do come from confusion
over whether it should be __init, __devinint etc .

We can argue later over the benefit of __exit ...

James

Re: Value of __*{init,exit} anotations?

[Russell King]

On Wed, Jan 30, 2008 at 04:44:12PM -0600, James Bottomley wrote:
> On Thu, 2008-01-31 at 00:32 +0200, Adrian Bunk wrote:
> > People at linux-arch (Cc'ed) might be better at explaining how often 
> > CONFIG_HOTPLUG gets used in real-life systems and how big the savings 
> > are there.
> > 
> > That might be a good basis for deciding whether it's worth it.
> 
> I'll certainly buy this.  Perhaps killing everything other than __init
> and __exit (meaning discardable whether the system is hotplug, suspend
> or whatever) might get rid of 90% of the problem while still preserving
> 90% of the benefits.  I think a lot of the issues do come from confusion
> over whether it should be __init, __devinint etc .

Just looking at HOTPLUG on ARM by a simple grep, 57 default configurations
for various machines are hotplug enabled out of 75 - so it's roughly 75%.
Whether that 25% remainder cares or not, I'm not sure.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:

Re: Value of __*{init,exit} anotations?

[Andi Kleen]

> Some people consider it worth it for their memory restricted systems
> and would like to drive the annotations even further. [1]

They could get much better bang-for-the-buck (as in memory saved
for amount of work invested) by tackling some the dynamic memory allocation
pigs.

In general it's a trade off between how much work and patch churn versus
benefit, and some of the annotations really don't look too good on this
scale.

> People at linux-arch (Cc'ed) might be better at explaining how often 
> CONFIG_HOTPLUG gets used in real-life systems and how big the savings 
> are there.

CONFIG_HOTPLUG is widely used for suspend on multi core systems. 

-Andi

Re: Value of __*{init,exit} anotations?

[Sam Ravnborg]

> > 
> > I don't deny we can invest large amounts of work to fix our current
> > issues and build large scriptable checks to ensure we keep it fixed ...
> > I'm just asking if, at the end of the day, it's really worth it.
> 
> Some people consider it worth it for their memory restricted systems
> and would like to drive the annotations even further. [1]
> 
> My experience while fixing section bugs during the last years is that 
> the __dev{init,exit}* are actually the main question since they are both 
> the majority of annotations and the ones that bring benefits only 
> in a case that has become very exotic (CONFIG_HOTPLUG=n).

Some numbers...
I my current tree with an allyesconfig build for x86 64bit I see:
136 Section mismatch warnings in total
99 Section mismatch warnings from drivers/

This is with a few patches of mine applied but none of the recently
posted fixes by Adrian.

I am concentrating on:
drivers/pci/
kernel/
mm/

Will post my patches during the weekend if things goes well.
There are some low hanging fruits in drivers/ but I stay away
from these from now expecting others to fix these.

	Sam

[PATCH] kill hotplug init/exit section annotations

[James Bottomley]

No-one seems to see much value in these, and they cause about 90% of our
problems with __init/__exit markers, so simply eliminate them.  Rather
than run over the whole tree removing them, this patch #defines them to
be nops.

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

---

I'll probably be going after __exit after this one, but it makes sense
to split them up, since the hotplug annotation removal looks
uncontroversial, whereas __exit and discard section removal might
produce more robust debate.  I also think doing the hotplug removal
gives us 90% of the benefits and removes 90% of the section mismatch
problems.

James


diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index f784d2f..5099021 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -9,46 +9,11 @@
 /* Align . to a 8 byte boundary equals to maximum function alignment. */
 #define ALIGN_FUNCTION()  . = ALIGN(8)
 
-/* The actual configuration determine if the init/exit sections
- * are handled as text/data or they can be discarded (which
- * often happens at runtime)
- */
-#ifdef CONFIG_HOTPLUG
-#define DEV_KEEP(sec)    *(.dev##sec)
-#define DEV_DISCARD(sec)
-#else
-#define DEV_KEEP(sec)
-#define DEV_DISCARD(sec) *(.dev##sec)
-#endif
-
-#ifdef CONFIG_HOTPLUG_CPU
-#define CPU_KEEP(sec)    *(.cpu##sec)
-#define CPU_DISCARD(sec)
-#else
-#define CPU_KEEP(sec)
-#define CPU_DISCARD(sec) *(.cpu##sec)
-#endif
-
-#if defined(CONFIG_MEMORY_HOTPLUG)
-#define MEM_KEEP(sec)    *(.mem##sec)
-#define MEM_DISCARD(sec)
-#else
-#define MEM_KEEP(sec)
-#define MEM_DISCARD(sec) *(.mem##sec)
-#endif
-
-
 /* .data section */
 #define DATA_DATA							\
 	*(.data)							\
 	*(.data.init.refok)						\
 	*(.ref.data)							\
-	DEV_KEEP(init.data)						\
-	DEV_KEEP(exit.data)						\
-	CPU_KEEP(init.data)						\
-	CPU_KEEP(exit.data)						\
-	MEM_KEEP(init.data)						\
-	MEM_KEEP(exit.data)						\
 	. = ALIGN(8);							\
 	VMLINUX_SYMBOL(__start___markers) = .;				\
 	*(__markers)							\
@@ -171,12 +136,6 @@
 	/* __*init sections */						\
 	__init_rodata : AT(ADDR(__init_rodata) - LOAD_OFFSET) {		\
 		*(.ref.rodata)						\
-		DEV_KEEP(init.rodata)					\
-		DEV_KEEP(exit.rodata)					\
-		CPU_KEEP(init.rodata)					\
-		CPU_KEEP(exit.rodata)					\
-		MEM_KEEP(init.rodata)					\
-		MEM_KEEP(exit.rodata)					\
 	}								\
 									\
 	/* Built-in module parameters. */				\
@@ -208,12 +167,6 @@
 		*(.ref.text)						\
 		*(.text.init.refok)					\
 		*(.exit.text.refok)					\
-	DEV_KEEP(init.text)						\
-	DEV_KEEP(exit.text)						\
-	CPU_KEEP(init.text)						\
-	CPU_KEEP(exit.text)						\
-	MEM_KEEP(init.text)						\
-	MEM_KEEP(exit.text)
 
 
 /* sched.text is aling to function alignment to secure we have same
@@ -241,33 +194,15 @@
 /* init and exit section handling */
 #define INIT_DATA							\
 	*(.init.data)							\
-	DEV_DISCARD(init.data)						\
-	DEV_DISCARD(init.rodata)					\
-	CPU_DISCARD(init.data)						\
-	CPU_DISCARD(init.rodata)					\
-	MEM_DISCARD(init.data)						\
-	MEM_DISCARD(init.rodata)
 
 #define INIT_TEXT							\
 	*(.init.text)							\
-	DEV_DISCARD(init.text)						\
-	CPU_DISCARD(init.text)						\
-	MEM_DISCARD(init.text)
 
 #define EXIT_DATA							\
 	*(.exit.data)							\
-	DEV_DISCARD(exit.data)						\
-	DEV_DISCARD(exit.rodata)					\
-	CPU_DISCARD(exit.data)						\
-	CPU_DISCARD(exit.rodata)					\
-	MEM_DISCARD(exit.data)						\
-	MEM_DISCARD(exit.rodata)
 
 #define EXIT_TEXT							\
 	*(.exit.text)							\
-	DEV_DISCARD(exit.text)						\
-	CPU_DISCARD(exit.text)						\
-	MEM_DISCARD(exit.text)
 
 		/* DWARF debug sections.
 		Symbols in the DWARF debugging sections are relative to
diff --git a/include/linux/init.h b/include/linux/init.h
index 2efbda0..225bd1c 100644
--- a/include/linux/init.h
+++ b/include/linux/init.h
@@ -81,29 +81,28 @@
 
 #define __exit          __section(.exit.text) __exitused __cold
 
-/* Used for HOTPLUG */
-#define __devinit        __section(.devinit.text) __cold
-#define __devinitdata    __section(.devinit.data)
-#define __devinitconst   __section(.devinit.rodata)
-#define __devexit        __section(.devexit.text) __exitused __cold
-#define __devexitdata    __section(.devexit.data)
-#define __devexitconst   __section(.devexit.rodata)
-
-/* Used for HOTPLUG_CPU */
-#define __cpuinit        __section(.cpuinit.text) __cold
-#define __cpuinitdata    __section(.cpuinit.data)
-#define __cpuinitconst   __section(.cpuinit.rodata)
-#define __cpuexit        __section(.cpuexit.text) __exitused __cold
-#define __cpuexitdata    __section(.cpuexit.data)
-#define __cpuexitconst   __section(.cpuexit.rodata)
+/* Legacy: originally used for HOTPLUG */
+#define __devinit        
+#define __devinitdata
+#define __devinitconst
+#define __devexit
+#define __devexitdata
+#define __devexitconst
+
+#define __cpuinit
+#define __cpuinitdata
+#define __cpuinitconst
+#define __cpuexit
+#define __cpuexitdata
+#define __cpuexitconst
 
 /* Used for MEMORY_HOTPLUG */
-#define __meminit        __section(.meminit.text) __cold
-#define __meminitdata    __section(.meminit.data)
-#define __meminitconst   __section(.meminit.rodata)
-#define __memexit        __section(.memexit.text) __exitused __cold
-#define __memexitdata    __section(.memexit.data)
-#define __memexitconst   __section(.memexit.rodata)
+#define __meminit
+#define __meminitdata
+#define __meminitconst
+#define __memexit
+#define __memexitdata
+#define __memexitconst
 
 /* For assembly routines */
 #define __INIT		.section	".init.text","ax"
@@ -111,14 +110,14 @@
 
 #define __INITDATA	.section	".init.data","aw"
 
-#define __DEVINIT        .section	".devinit.text", "ax"
-#define __DEVINITDATA    .section	".devinit.data", "aw"
+#define __DEVINIT
+#define __DEVINITDATA
 
-#define __CPUINIT        .section	".cpuinit.text", "ax"
-#define __CPUINITDATA    .section	".cpuinit.data", "aw"
+#define __CPUINIT
+#define __CPUINITDATA
 
-#define __MEMINIT        .section	".meminit.text", "ax"
-#define __MEMINITDATA    .section	".meminit.data", "aw"
+#define __MEMINIT
+#define __MEMINITDATA
 
 /* silence warnings when references are OK */
 #define __REF            .section       ".ref.text", "ax"

Re: [PATCH] kill hotplug init/exit section annotations

[Arjan van de Ven]

On Thu, 31 Jan 2008 09:57:31 -0600
James Bottomley <James.Bottomley@HansenPartnership.com> wrote:

> No-one seems to see much value in these, and they cause about 90% of
> our problems with __init/__exit markers, so simply eliminate them.
> Rather than run over the whole tree removing them, this patch
> #defines them to be nops.
> 
> Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
> 
> ---
> 
> I'll probably be going after __exit after this one, but it makes sense
> to split them up, since the hotplug annotation removal looks
> uncontroversial, whereas __exit and discard section removal might
> produce more robust debate.  I also think doing the hotplug removal
> gives us 90% of the benefits and removes 90% of the section mismatch
> problems.


Since hotplug is so fundamental nowadays the value no longer outweighs the pain/cost
to me, so 

Acked-by: Arjan van de Ven <arjan@linux.intel.com>

-- 
If you want to reach me at my work email, use arjan@linux.intel.com
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org

Re: [PATCH] kill hotplug init/exit section annotations

[Adrian Bunk]

On Thu, Jan 31, 2008 at 08:11:20AM -0800, Arjan van de Ven wrote:
> On Thu, 31 Jan 2008 09:57:31 -0600
> James Bottomley <James.Bottomley@HansenPartnership.com> wrote:
> 
> > No-one seems to see much value in these, and they cause about 90% of
> > our problems with __init/__exit markers, so simply eliminate them.
> > Rather than run over the whole tree removing them, this patch
> > #defines them to be nops.
> > 
> > Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
> > 
> > ---
> > 
> > I'll probably be going after __exit after this one, but it makes sense
> > to split them up, since the hotplug annotation removal looks
> > uncontroversial, whereas __exit and discard section removal might
> > produce more robust debate.  I also think doing the hotplug removal
> > gives us 90% of the benefits and removes 90% of the section mismatch
> > problems.
> 
> 
> Since hotplug is so fundamental nowadays the value no longer outweighs the pain/cost
> to me, so 

Granted for normal hotplug.

But my computer has neither CPU hotplug not memory hotplug, and I don't 
see the point for removing these annotations (and they are anyway not 
what causes problems in normal drivers).

> Acked-by: Arjan van de Ven <arjan@linux.intel.com>

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

Re: [PATCH] kill hotplug init/exit section annotations

[Arjan van de Ven]

On Thu, 31 Jan 2008 18:21:42 +0200
Adrian Bunk <bunk@kernel.org> wrote:

> On Thu, Jan 31, 2008 at 08:11:20AM -0800, Arjan van de Ven wrote:
> > On Thu, 31 Jan 2008 09:57:31 -0600
> > James Bottomley <James.Bottomley@HansenPartnership.com> wrote:
> > 
> > > No-one seems to see much value in these, and they cause about 90%
> > > of our problems with __init/__exit markers, so simply eliminate
> > > them. Rather than run over the whole tree removing them, this
> > > patch #defines them to be nops.
> > > 
> > > Signed-off-by: James Bottomley
> > > <James.Bottomley@HansenPartnership.com>
> > > 
> > > ---
> > > 
> > > I'll probably be going after __exit after this one, but it makes
> > > sense to split them up, since the hotplug annotation removal looks
> > > uncontroversial, whereas __exit and discard section removal might
> > > produce more robust debate.  I also think doing the hotplug
> > > removal gives us 90% of the benefits and removes 90% of the
> > > section mismatch problems.
> > 
> > 
> > Since hotplug is so fundamental nowadays the value no longer
> > outweighs the pain/cost to me, so 
> 
> Granted for normal hotplug.
> 
> But my computer has neither CPU hotplug 


cpuhotplug is required for suspend/resume.



-- 
If you want to reach me at my work email, use arjan@linux.intel.com
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org

Re: [PATCH] kill hotplug init/exit section annotations

[Adrian Bunk]

On Thu, Jan 31, 2008 at 09:07:49AM -0800, Arjan van de Ven wrote:
> On Thu, 31 Jan 2008 18:21:42 +0200
> Adrian Bunk <bunk@kernel.org> wrote:
> 
> > On Thu, Jan 31, 2008 at 08:11:20AM -0800, Arjan van de Ven wrote:
> > > On Thu, 31 Jan 2008 09:57:31 -0600
> > > James Bottomley <James.Bottomley@HansenPartnership.com> wrote:
> > > 
> > > > No-one seems to see much value in these, and they cause about 90%
> > > > of our problems with __init/__exit markers, so simply eliminate
> > > > them. Rather than run over the whole tree removing them, this
> > > > patch #defines them to be nops.
> > > > 
> > > > Signed-off-by: James Bottomley
> > > > <James.Bottomley@HansenPartnership.com>
> > > > 
> > > > ---
> > > > 
> > > > I'll probably be going after __exit after this one, but it makes
> > > > sense to split them up, since the hotplug annotation removal looks
> > > > uncontroversial, whereas __exit and discard section removal might
> > > > produce more robust debate.  I also think doing the hotplug
> > > > removal gives us 90% of the benefits and removes 90% of the
> > > > section mismatch problems.
> > > 
> > > 
> > > Since hotplug is so fundamental nowadays the value no longer
> > > outweighs the pain/cost to me, so 
> > 
> > Granted for normal hotplug.
> > 
> > But my computer has neither CPU hotplug 
> 
> cpuhotplug is required for suspend/resume.

Not on UP computers.

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

Re: [PATCH] kill hotplug init/exit section annotations

[Chris Wedgwood]

On Thu, Jan 31, 2008 at 07:14:36PM +0200, Adrian Bunk wrote:

> > cpuhotplug is required for suspend/resume.
>
> Not on UP computers.

those are less and less common now, most modern laptops are dual core

Re: [PATCH] kill hotplug init/exit section annotations

[Arjan van de Ven]

On Thu, 31 Jan 2008 19:14:36 +0200
Adrian Bunk <bunk@kernel.org> wrote:
> > cpuhotplug is required for suspend/resume.
> 
> Not on UP computers.
> 

great! someone who still has one of those and uses a kernel without it.
Can you look at your system.map and see how many kilobytes you've gained?
Eg how many kilobytes are in these sections exactly?
(but also subtract any cost due to page aligning this stuff ;-)

> cu
> Adrian
> 


-- 
If you want to reach me at my work email, use arjan@linux.intel.com
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org

Re: [PATCH] kill hotplug init/exit section annotations

[Adrian Bunk]

On Thu, Jan 31, 2008 at 09:45:26AM -0800, Chris Wedgwood wrote:
> On Thu, Jan 31, 2008 at 07:14:36PM +0200, Adrian Bunk wrote:
> 
> > > cpuhotplug is required for suspend/resume.
> >
> > Not on UP computers.
> 
> those are less and less common now, most modern laptops are dual core

Who was talking about laptops?

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

Re: [PATCH] kill hotplug init/exit section annotations

[Chris Wedgwood]

On Thu, Jan 31, 2008 at 07:55:43PM +0200, Adrian Bunk wrote:

> Who was talking about laptops?

If laptops are mostly MP these days, then 'desktops' and 'servers'
certainly are --- so pretty much everyone needs CPU hotplug.

Re: [PATCH] kill hotplug init/exit section annotations

[Sam Ravnborg]

On Thu, Jan 31, 2008 at 09:48:01AM -0800, Arjan van de Ven wrote:
> On Thu, 31 Jan 2008 19:14:36 +0200
> Adrian Bunk <bunk@kernel.org> wrote:
> > > cpuhotplug is required for suspend/resume.
> > 
> > Not on UP computers.
> > 
> 
> great! someone who still has one of those and uses a kernel without it.
> Can you look at your system.map and see how many kilobytes you've gained?
> Eg how many kilobytes are in these sections exactly?
I have one. A Atmel AT91 board equipped with an 9263.
So lets take a look at the defconfig build for the evaluation board.


o-arm/vmlinux.o:     file format elf32-littlearm

  0 .text         001cdefc  00000000  00000000  00000400  2**10
  2 .init.text    000165e8  00000000  00000000  001ce6c0  2**5
 26 .init.data    000032ec  00000000  00000000  002578cc  2**2

---

  4 .devinit.text 00001558  00000000  00000000  001e5270  2**2
  9 .exit.text    00000bc8  00000000  00000000  001e8d2c  2**2
 10 .cpuinit.text 00000924  00000000  00000000  001e98f4  2**2
 11 .meminit.text 000004cc  00000000  00000000  001ea218  2**2
 12 .devexit.text 00000160  00000000  00000000  001ea6e4  2**2
 38 .cpuinit.data 00000040  00000000  00000000  0025afc0  2**2
 39 .meminit.data 0000000c  00000000  00000000  0025b000  2**2


__devinit alone gives a net win of 5464 bytes.
That is only ~3% of total .text size but this is non-swapable
memory where everything is worth it.
And the configuration selected is by no means optimal
with respect to minimal size.

	Sam

Re: [PATCH] kill hotplug init/exit section annotations

[Arjan van de Ven]

On Thu, 31 Jan 2008 19:34:25 +0100
Sam Ravnborg <sam@ravnborg.org> wrote:

> On Thu, Jan 31, 2008 at 09:48:01AM -0800, Arjan van de Ven wrote:
> > On Thu, 31 Jan 2008 19:14:36 +0200
> > Adrian Bunk <bunk@kernel.org> wrote:
> > > > cpuhotplug is required for suspend/resume.
> > > 
> > > Not on UP computers.
> > > 
> > 
> > great! someone who still has one of those and uses a kernel without
> > it. Can you look at your system.map and see how many kilobytes
> > you've gained? Eg how many kilobytes are in these sections exactly?
> I have one. A Atmel AT91 board equipped with an 9263.
> So lets take a look at the defconfig build for the evaluation board.
> 
> 
> o-arm/vmlinux.o:     file format elf32-littlearm
> 
>   0 .text         001cdefc  00000000  00000000  00000400  2**10
>   2 .init.text    000165e8  00000000  00000000  001ce6c0  2**5
>  26 .init.data    000032ec  00000000  00000000  002578cc  2**2
> 
> ---
> 
>   4 .devinit.text 00001558  00000000  00000000  001e5270  2**2
>   9 .exit.text    00000bc8  00000000  00000000  001e8d2c  2**2
>  10 .cpuinit.text 00000924  00000000  00000000  001e98f4  2**2
>  11 .meminit.text 000004cc  00000000  00000000  001ea218  2**2
>  12 .devexit.text 00000160  00000000  00000000  001ea6e4  2**2
>  38 .cpuinit.data 00000040  00000000  00000000  0025afc0  2**2
>  39 .meminit.data 0000000c  00000000  00000000  0025b000  2**2
> 
> 
> __devinit alone gives a net win of 5464 bytes.
> That is only ~3% of total .text size but this is non-swapable
> memory where everything is worth it.

now how much of this is lost again because you have to round the stuff to pagesize?

Re: [PATCH] kill hotplug init/exit section annotations

[Geert Uytterhoeven]

On Thu, 31 Jan 2008, Chris Wedgwood wrote:
> On Thu, Jan 31, 2008 at 07:55:43PM +0200, Adrian Bunk wrote:
> > Who was talking about laptops?
> 
> If laptops are mostly MP these days, then 'desktops' and 'servers'
> certainly are --- so pretty much everyone needs CPU hotplug.

<irony>
Thank you for giving an exhaustive list of classes of machines Linux runs on!
</irony>

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds

Re: [PATCH] kill hotplug init/exit section annotations

[Sam Ravnborg]

On Thu, Jan 31, 2008 at 10:48:11AM -0800, Arjan van de Ven wrote:
> On Thu, 31 Jan 2008 19:34:25 +0100
> Sam Ravnborg <sam@ravnborg.org> wrote:
> 
> > On Thu, Jan 31, 2008 at 09:48:01AM -0800, Arjan van de Ven wrote:
> > > On Thu, 31 Jan 2008 19:14:36 +0200
> > > Adrian Bunk <bunk@kernel.org> wrote:
> > > > > cpuhotplug is required for suspend/resume.
> > > > 
> > > > Not on UP computers.
> > > > 
> > > 
> > > great! someone who still has one of those and uses a kernel without
> > > it. Can you look at your system.map and see how many kilobytes
> > > you've gained? Eg how many kilobytes are in these sections exactly?
> > I have one. A Atmel AT91 board equipped with an 9263.
> > So lets take a look at the defconfig build for the evaluation board.
> > 
> > 
> > o-arm/vmlinux.o:     file format elf32-littlearm
> > 
> >   0 .text         001cdefc  00000000  00000000  00000400  2**10
> >   2 .init.text    000165e8  00000000  00000000  001ce6c0  2**5
> >  26 .init.data    000032ec  00000000  00000000  002578cc  2**2
> > 
> > ---
> > 
> >   4 .devinit.text 00001558  00000000  00000000  001e5270  2**2
> >   9 .exit.text    00000bc8  00000000  00000000  001e8d2c  2**2
> >  10 .cpuinit.text 00000924  00000000  00000000  001e98f4  2**2
> >  11 .meminit.text 000004cc  00000000  00000000  001ea218  2**2
> >  12 .devexit.text 00000160  00000000  00000000  001ea6e4  2**2
> >  38 .cpuinit.data 00000040  00000000  00000000  0025afc0  2**2
> >  39 .meminit.data 0000000c  00000000  00000000  0025b000  2**2
> > 
> > 
> > __devinit alone gives a net win of 5464 bytes.
> > That is only ~3% of total .text size but this is non-swapable
> > memory where everything is worth it.
> 
> now how much of this is lost again because you have to round the stuff to pagesize?

Lets take a look in the ARM vmlinux.lds.S file:
       .text.head : {
                _stext = .;
                _sinittext = .;
                *(.text.head)
        }

        .init : {                       /* Init code and data           */
                        INIT_TEXT
                _einittext = .;
                __proc_info_begin = .;
                        *(.proc.info.init)
                __proc_info_end = .;
                __arch_info_begin = .;
                        *(.arch.info.init)
                __arch_info_end = .;
                __tagtable_begin = .;
                        *(.taglist.init)
                __tagtable_end = .;
                . = ALIGN(16);
                __setup_start = .;
                        *(.init.setup)
                __setup_end = .;
                __early_begin = .;
                        *(.early_param.init)
                __early_end = .;
                __initcall_start = .;
                        INITCALLS
                __initcall_end = .;
                __con_initcall_start = .;
                        *(.con_initcall.init)
                __con_initcall_end = .;
                __security_initcall_start = .;
                        *(.security_initcall.init)
                __security_initcall_end = .;
#ifdef CONFIG_BLK_DEV_INITRD
                . = ALIGN(32);
                __initramfs_start = .;
                        usr/built-in.o(.init.ramfs)
                __initramfs_end = .;
#endif
                . = ALIGN(4096);
                __per_cpu_start = .;
                        *(.data.percpu)
                        *(.data.percpu.shared_aligned)
                __per_cpu_end = .;
#ifndef CONFIG_XIP_KERNEL
                __init_begin = _stext;
                INIT_DATA
                . = ALIGN(4096);
                __init_end = .;

Everything between _stext and __init_end are freed.
And we have two PAGESIZE alignmnets here - one for the percpu stuff
and the other to align the full area that can be freed.
So there is no special alignment for the __devinit stuff.

And there is no percpu data on ARM so that area is empty.
So it is one or two pages extra that are freed up.

	Sam