[patch 01/2] allow gcc4 to control inlining

[patch 01/2] allow gcc4 to control inlining

[Ingo Molnar]

allow gcc4 compilers to decide what to inline and what not - instead
of the kernel forcing gcc to inline all the time.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arjan van de Ven <arjan@infradead.org>
----

 include/linux/compiler-gcc4.h |    9 +++++----
 1 files changed, 5 insertions(+), 4 deletions(-)

Index: linux/include/linux/compiler-gcc4.h
===================================================================
--- linux.orig/include/linux/compiler-gcc4.h
+++ linux/include/linux/compiler-gcc4.h
@@ -3,14 +3,15 @@
 /* These definitions are for GCC v4.x.  */
 #include <linux/compiler-gcc.h>
 
-#define inline			inline		__attribute__((always_inline))
-#define __inline__		__inline__	__attribute__((always_inline))
-#define __inline		__inline	__attribute__((always_inline))
+#define inline			inline
+#define __inline__		__inline__
+#define __inline		__inline
 #define __deprecated		__attribute__((deprecated))
 #define __attribute_used__	__attribute__((__used__))
 #define __attribute_pure__	__attribute__((pure))
 #define __attribute_const__	__attribute__((__const__))
-#define  noinline		__attribute__((noinline))
+#define noinline		__attribute__((noinline))
+#define __always_inline		inline __attribute__((always_inline))
 #define __must_check 		__attribute__((warn_unused_result))
 #define __compiler_offsetof(a,b) __builtin_offsetof(a,b)
 

Re: [patch 01/2] allow gcc4 to control inlining

[Matt Mackall]

On Wed, Dec 28, 2005 at 12:46:53PM +0100, Ingo Molnar wrote:
> allow gcc4 compilers to decide what to inline and what not - instead
> of the kernel forcing gcc to inline all the time.
> 
> Signed-off-by: Ingo Molnar <mingo@elte.hu>
> Signed-off-by: Arjan van de Ven <arjan@infradead.org>

I'm ever so slightly wary of GCC 4's stack size logic for functions with
nested scopes, but I think we'll have no trouble catching any trouble
cases in 2.6.16-rc.

Acked-by: Matt Mackall <mpm@selenic.com>

-- 
Mathematics is the supreme nostalgia of our time.

Re: [patch 01/2] allow gcc4 to control inlining

[Ingo Molnar]

* Matt Mackall <mpm@selenic.com> wrote:

> On Wed, Dec 28, 2005 at 12:46:53PM +0100, Ingo Molnar wrote:
> > allow gcc4 compilers to decide what to inline and what not - instead
> > of the kernel forcing gcc to inline all the time.
> > 
> > Signed-off-by: Ingo Molnar <mingo@elte.hu>
> > Signed-off-by: Arjan van de Ven <arjan@infradead.org>
> 
> I'm ever so slightly wary of GCC 4's stack size logic for functions 
> with nested scopes, but I think we'll have no trouble catching any 
> trouble cases in 2.6.16-rc.
> 
> Acked-by: Matt Mackall <mpm@selenic.com>

FYI, the max function-frame size did not change, so there's no 
outrageous frames like with gcc3, just a small shift upwards.

	Ingo

Re: [patch 01/2] allow gcc4 to control inlining

[Matt Mackall]

On Wed, Dec 28, 2005 at 03:34:42PM +0100, Ingo Molnar wrote:
> 
> * Matt Mackall <mpm@selenic.com> wrote:
> 
> > On Wed, Dec 28, 2005 at 12:46:53PM +0100, Ingo Molnar wrote:
> > > allow gcc4 compilers to decide what to inline and what not - instead
> > > of the kernel forcing gcc to inline all the time.
> > > 
> > > Signed-off-by: Ingo Molnar <mingo@elte.hu>
> > > Signed-off-by: Arjan van de Ven <arjan@infradead.org>
> > 
> > I'm ever so slightly wary of GCC 4's stack size logic for functions 
> > with nested scopes, but I think we'll have no trouble catching any 
> > trouble cases in 2.6.16-rc.
> > 
> > Acked-by: Matt Mackall <mpm@selenic.com>
> 
> FYI, the max function-frame size did not change, so there's no 
> outrageous frames like with gcc3, just a small shift upwards.

My point is more that I wouldn't be surprised if we found a corner
case for a particular .config. But even with GCC 3 and 4k stacks,
automatic inlining worked just fine for most configs after killing
just a few offenders.

-- 
Mathematics is the supreme nostalgia of our time.

Re: [patch 01/2] allow gcc4 to control inlining

[Roland Dreier]

 > -#define inline			inline		__attribute__((always_inline))
 > -#define __inline__		__inline__	__attribute__((always_inline))
 > -#define __inline		__inline	__attribute__((always_inline))

Why not just delete these lines?  This:

 > +#define inline			inline
 > +#define __inline__		__inline__
 > +#define __inline		__inline

seems pointless to me.

 - R.

Re: [patch 01/2] allow gcc4 to control inlining

[Ingo Molnar]

* Roland Dreier <rdreier@cisco.com> wrote:

>  > -#define inline			inline		__attribute__((always_inline))
>  > -#define __inline__		__inline__	__attribute__((always_inline))
>  > -#define __inline		__inline	__attribute__((always_inline))
> 
> Why not just delete these lines?  This:
> 
>  > +#define inline			inline
>  > +#define __inline__		__inline__
>  > +#define __inline		__inline
> 
> seems pointless to me.

indeed. I thought they were redefined to a default if not defined, but 
that's only the case for __always_inline. Updated patch below.

	Ingo

--------
Subject: allow gcc4 to control inlining

allow gcc4 compilers to decide what to inline and what not - instead
of the kernel forcing gcc to inline all the time.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arjan van de Ven <arjan@infradead.org>
----

 include/linux/compiler-gcc4.h |    6 ++----
 1 files changed, 2 insertions(+), 4 deletions(-)

Index: linux/include/linux/compiler-gcc4.h
===================================================================
--- linux.orig/include/linux/compiler-gcc4.h
+++ linux/include/linux/compiler-gcc4.h
@@ -3,14 +3,12 @@
 /* These definitions are for GCC v4.x.  */
 #include <linux/compiler-gcc.h>
 
-#define inline			inline		__attribute__((always_inline))
-#define __inline__		__inline__	__attribute__((always_inline))
-#define __inline		__inline	__attribute__((always_inline))
 #define __deprecated		__attribute__((deprecated))
 #define __attribute_used__	__attribute__((__used__))
 #define __attribute_pure__	__attribute__((pure))
 #define __attribute_const__	__attribute__((__const__))
-#define  noinline		__attribute__((noinline))
+#define noinline		__attribute__((noinline))
+#define __always_inline		inline __attribute__((always_inline))
 #define __must_check 		__attribute__((warn_unused_result))
 #define __compiler_offsetof(a,b) __builtin_offsetof(a,b)
 

Re: [patch 01/2] allow gcc4 to control inlining

[Al Viro]

On Wed, Dec 28, 2005 at 12:46:53PM +0100, Ingo Molnar wrote:
> allow gcc4 compilers to decide what to inline and what not - instead
> of the kernel forcing gcc to inline all the time.

> +#define noinline		__attribute__((noinline))
> +#define __always_inline		inline __attribute__((always_inline))
>  #define __must_check 		__attribute__((warn_unused_result))
>  #define __compiler_offsetof(a,b) __builtin_offsetof(a,b)

You seem to be missing the rest of the patch - namely, addition of
always_inline where it is needed now...

Note that we *do* need it in quite a few places.  Anything that relies on
dead code elimination to kill a call of function that doesn't exist
would better be always inlined...

Re: [patch 01/2] allow gcc4 to control inlining

[Arjan van de Ven]

On Wed, 2005-12-28 at 18:39 +0000, Al Viro wrote:
> On Wed, Dec 28, 2005 at 12:46:53PM +0100, Ingo Molnar wrote:
> > allow gcc4 compilers to decide what to inline and what not - instead
> > of the kernel forcing gcc to inline all the time.
> 
> > +#define noinline		__attribute__((noinline))
> > +#define __always_inline		inline __attribute__((always_inline))
> >  #define __must_check 		__attribute__((warn_unused_result))
> >  #define __compiler_offsetof(a,b) __builtin_offsetof(a,b)
> 
> You seem to be missing the rest of the patch - namely, addition of
> always_inline where it is needed now...
> 
> Note that we *do* need it in quite a few places.  Anything that relies on
> dead code elimination to kill a call of function that doesn't exist
> would better be always inlined...

on x86-64 that seems to only be fix_to_virt though.. so it's really not
that many.

(based on making "inline" a define for noinline and then an
allyesconfig)